/*
 * Copyright (C) 2017 Denys Vlasenko
 *
 * Licensed under GPLv2, see file LICENSE in this source tree.
 */
//config:config TLS
//config:       bool #No description makes it a hidden option
//config:       default n
//Note:
//Config.src also defines FEATURE_TLS_SHA1 option

//kbuild:lib-$(CONFIG_TLS) += tls.o
//kbuild:lib-$(CONFIG_TLS) += tls_pstm.o
//kbuild:lib-$(CONFIG_TLS) += tls_pstm_montgomery_reduce.o
//kbuild:lib-$(CONFIG_TLS) += tls_pstm_mul_comba.o
//kbuild:lib-$(CONFIG_TLS) += tls_pstm_sqr_comba.o
//kbuild:lib-$(CONFIG_TLS) += tls_aes.o
//kbuild:lib-$(CONFIG_TLS) += tls_aesgcm.o
//kbuild:lib-$(CONFIG_TLS) += tls_rsa.o
//kbuild:lib-$(CONFIG_TLS) += tls_fe.o

#include "tls.h"

// works against "openssl s_server -cipher NULL"
// and against wolfssl-3.9.10-stable/examples/server/server.c:
#define ALLOW_RSA_NULL_SHA256  0  // for testing (does everything except encrypting)

//Tested against kernel.org:
//#define CIPHER_ID TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA // ok, recvs SERVER_KEY_EXCHANGE *** matrixssl uses this on my box
//#define CIPHER_ID TLS_RSA_WITH_AES_256_CBC_SHA256 // ok, no SERVER_KEY_EXCHANGE
//#define CIPHER_ID TLS_DH_anon_WITH_AES_256_CBC_SHA // SSL_ALERT_HANDSHAKE_FAILURE
//^^^^^^^^^^^^^^^^^^^^^^^ (tested b/c this one doesn't req server certs... no luck, server refuses it)
//#define CIPHER_ID TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 // SSL_ALERT_HANDSHAKE_FAILURE
//#define CIPHER_ID TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 // SSL_ALERT_HANDSHAKE_FAILURE
//#define CIPHER_ID TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 // ok, recvs SERVER_KEY_EXCHANGE
//#define CIPHER_ID TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
//#define CIPHER_ID TLS_ECDH_ECDSA_WITH_AES_256_GCM_SHA384
//#define CIPHER_ID TLS_ECDH_ECDSA_WITH_AES_128_GCM_SHA256 // SSL_ALERT_HANDSHAKE_FAILURE
//#define CIPHER_ID TLS_ECDH_RSA_WITH_AES_256_GCM_SHA384
//#define CIPHER_ID TLS_ECDH_RSA_WITH_AES_128_GCM_SHA256 // SSL_ALERT_HANDSHAKE_FAILURE
//#define CIPHER_ID TLS_RSA_WITH_AES_256_GCM_SHA384 // ok, no SERVER_KEY_EXCHANGE
//#define CIPHER_ID TLS_RSA_WITH_AES_128_GCM_SHA256 // ok, no SERVER_KEY_EXCHANGE

// works against wolfssl-3.9.10-stable/examples/server/server.c
// works for kernel.org
// does not work for cdn.kernel.org (e.g. downloading an actual tarball, not a web page)
//  getting alert 40 "handshake failure" at once
//  with GNU Wget 1.18, they agree on TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (0xC02F) cipher
//  fail: openssl s_client -connect cdn.kernel.org:443 -debug -tls1_2 -cipher AES256-SHA256
//  fail: openssl s_client -connect cdn.kernel.org:443 -debug -tls1_2 -cipher AES256-GCM-SHA384
//  fail: openssl s_client -connect cdn.kernel.org:443 -debug -tls1_2 -cipher AES128-SHA256
//  ok:   openssl s_client -connect cdn.kernel.org:443 -debug -tls1_2 -cipher AES128-GCM-SHA256
//  ok:   openssl s_client -connect cdn.kernel.org:443 -debug -tls1_2 -cipher AES128-SHA
//        (TLS_RSA_WITH_AES_128_CBC_SHA - in TLS 1.2 it's mandated to be always supported)
//#define CIPHER_ID1  TLS_RSA_WITH_AES_256_CBC_SHA256 //0x003D
// Works with "wget https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.9.5.tar.xz"
//#define CIPHER_ID2  TLS_RSA_WITH_AES_128_CBC_SHA    //0x002F

// bug #11456:
// ftp.openbsd.org only supports ECDHE-RSA-AESnnn-GCM-SHAnnn or ECDHE-RSA-CHACHA20-POLY1305
//#define CIPHER_ID3  TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 //0xC02F
// host is.gd accepts only ECDHE-ECDSA-foo (the simplest which works: ECDHE-ECDSA-AES128-SHA 0xC009)
//#define CIPHER_ID4  TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA  //0xC009


#define TLS_DEBUG      0
#define TLS_DEBUG_HASH 0
#define TLS_DEBUG_DER  0
#define TLS_DEBUG_FIXED_SECRETS 0
#if 0
# define dump_raw_out(...) dump_hex(__VA_ARGS__)
#else
# define dump_raw_out(...) ((void)0)
#endif
#if 0
# define dump_raw_in(...) dump_hex(__VA_ARGS__)
#else
# define dump_raw_in(...) ((void)0)
#endif

#if TLS_DEBUG
# define dbg(...) fprintf(stderr, __VA_ARGS__)
#else
# define dbg(...) ((void)0)
#endif

#if TLS_DEBUG_DER
# define dbg_der(...) fprintf(stderr, __VA_ARGS__)
#else
# define dbg_der(...) ((void)0)
#endif


//TLS 1.2
#define TLS_MAJ 3
#define TLS_MIN 3

#define RECORD_TYPE_CHANGE_CIPHER_SPEC  20 /* 0x14 */
#define RECORD_TYPE_ALERT               21 /* 0x15 */
#define RECORD_TYPE_HANDSHAKE           22 /* 0x16 */
#define RECORD_TYPE_APPLICATION_DATA    23 /* 0x17 */

#define HANDSHAKE_HELLO_REQUEST         0  /* 0x00 */
#define HANDSHAKE_CLIENT_HELLO          1  /* 0x01 */
#define HANDSHAKE_SERVER_HELLO          2  /* 0x02 */
#define HANDSHAKE_HELLO_VERIFY_REQUEST  3  /* 0x03 */
#define HANDSHAKE_NEW_SESSION_TICKET    4  /* 0x04 */
#define HANDSHAKE_CERTIFICATE           11 /* 0x0b */
#define HANDSHAKE_SERVER_KEY_EXCHANGE   12 /* 0x0c */
#define HANDSHAKE_CERTIFICATE_REQUEST   13 /* 0x0d */
#define HANDSHAKE_SERVER_HELLO_DONE     14 /* 0x0e */
#define HANDSHAKE_CERTIFICATE_VERIFY    15 /* 0x0f */
#define HANDSHAKE_CLIENT_KEY_EXCHANGE   16 /* 0x10 */
#define HANDSHAKE_FINISHED              20 /* 0x14 */

#define TLS_EMPTY_RENEGOTIATION_INFO_SCSV       0x00FF /* not a real cipher id... */

#define SSL_NULL_WITH_NULL_NULL                 0x0000
#define SSL_RSA_WITH_NULL_MD5                   0x0001
#define SSL_RSA_WITH_NULL_SHA                   0x0002
#define SSL_RSA_WITH_RC4_128_MD5                0x0004
#define SSL_RSA_WITH_RC4_128_SHA                0x0005
#define TLS_RSA_WITH_IDEA_CBC_SHA               0x0007  /* 7 */
#define SSL_RSA_WITH_3DES_EDE_CBC_SHA           0x000A  /* 10 */

#define SSL_DHE_RSA_WITH_3DES_EDE_CBC_SHA       0x0016  /* 22 */
#define SSL_DH_anon_WITH_RC4_128_MD5            0x0018  /* 24 */
#define SSL_DH_anon_WITH_3DES_EDE_CBC_SHA       0x001B  /* 27 */
#define TLS_RSA_WITH_AES_128_CBC_SHA            0x002F  /*SSLv3   Kx=RSA   Au=RSA   Enc=AES(128) Mac=SHA1 */
#define TLS_DHE_RSA_WITH_AES_128_CBC_SHA        0x0033  /* 51 */
#define TLS_DH_anon_WITH_AES_128_CBC_SHA        0x0034  /* 52 */
#define TLS_RSA_WITH_AES_256_CBC_SHA            0x0035  /* 53 */
#define TLS_DHE_RSA_WITH_AES_256_CBC_SHA        0x0039  /* 57 */
#define TLS_DH_anon_WITH_AES_256_CBC_SHA        0x003A  /* 58 */
#define TLS_RSA_WITH_NULL_SHA256                0x003B  /* 59 */
#define TLS_RSA_WITH_AES_128_CBC_SHA256         0x003C  /* 60 */
#define TLS_RSA_WITH_AES_256_CBC_SHA256         0x003D  /* 61 */
#define TLS_DHE_RSA_WITH_AES_128_CBC_SHA256     0x0067  /* 103 */
#define TLS_DHE_RSA_WITH_AES_256_CBC_SHA256     0x006B  /* 107 */
#define TLS_PSK_WITH_AES_128_CBC_SHA            0x008C  /* 140 */
#define TLS_PSK_WITH_AES_256_CBC_SHA            0x008D  /* 141 */
#define TLS_DHE_PSK_WITH_AES_128_CBC_SHA        0x0090  /* 144 */
#define TLS_DHE_PSK_WITH_AES_256_CBC_SHA        0x0091  /* 145 */
#define TLS_RSA_WITH_SEED_CBC_SHA               0x0096  /* 150 */
#define TLS_RSA_WITH_AES_128_GCM_SHA256         0x009C  /*TLSv1.2 Kx=RSA   Au=RSA   Enc=AESGCM(128) Mac=AEAD */
#define TLS_RSA_WITH_AES_256_GCM_SHA384         0x009D  /*TLSv1.2 Kx=RSA   Au=RSA   Enc=AESGCM(256) Mac=AEAD */
#define TLS_DHE_RSA_WITH_AES_128_GCM_SHA256     0x009E  /*TLSv1.2 Kx=DH    Au=RSA   Enc=AESGCM(128) Mac=AEAD */
#define TLS_DHE_RSA_WITH_AES_256_GCM_SHA384     0x009F  /*TLSv1.2 Kx=DH    Au=RSA   Enc=AESGCM(256) Mac=AEAD */
#define TLS_DH_anon_WITH_AES_128_GCM_SHA256     0x00A6  /* RFC 5288 */
#define TLS_DH_anon_WITH_AES_256_GCM_SHA384     0x00A7  /* RFC 5288 */
#define TLS_PSK_WITH_AES_128_CBC_SHA256         0x00AE  /* 174 */
#define TLS_PSK_WITH_AES_256_CBC_SHA384         0x00AF  /* 175 */
#define TLS_ECDH_ECDSA_WITH_AES_128_CBC_SHA     0xC004  /* 49156 */
#define TLS_ECDH_ECDSA_WITH_AES_256_CBC_SHA     0xC005  /* 49157 */
#define TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA    0xC009  /*TLSv1   Kx=ECDH  Au=ECDSA Enc=AES(128) Mac=SHA1 */
#define TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA    0xC00A  /*TLSv1   Kx=ECDH  Au=ECDSA Enc=AES(256) Mac=SHA1 */
#define TLS_ECDH_RSA_WITH_AES_128_CBC_SHA       0xC00E  /* 49166 */
#define TLS_ECDH_RSA_WITH_AES_256_CBC_SHA       0xC00F  /* 49167 */
#define TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA     0xC012  /* 49170 */
#define TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA      0xC013  /*TLSv1   Kx=ECDH  Au=RSA   Enc=AES(128) Mac=SHA1 */
#define TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA      0xC014  /*TLSv1   Kx=ECDH  Au=RSA   Enc=AES(256) Mac=SHA1 */
#define TLS_ECDH_anon_WITH_AES_128_CBC_SHA      0xC018  /* RFC 4492 */
#define TLS_ECDH_anon_WITH_AES_256_CBC_SHA      0xC019  /* RFC 4492 */
#define TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256 0xC023  /*TLSv1.2 Kx=ECDH  Au=ECDSA Enc=AES(128) Mac=SHA256 */
#define TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384 0xC024  /*TLSv1.2 Kx=ECDH  Au=ECDSA Enc=AES(256) Mac=SHA384 */
#define TLS_ECDH_ECDSA_WITH_AES_128_CBC_SHA256  0xC025  /* 49189 */
#define TLS_ECDH_ECDSA_WITH_AES_256_CBC_SHA384  0xC026  /* 49190 */
#define TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256   0xC027  /*TLSv1.2 Kx=ECDH  Au=RSA   Enc=AES(128) Mac=SHA256 */
#define TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384   0xC028  /*TLSv1.2 Kx=ECDH  Au=RSA   Enc=AES(256) Mac=SHA384 */
#define TLS_ECDH_RSA_WITH_AES_128_CBC_SHA256    0xC029  /* 49193 */
#define TLS_ECDH_RSA_WITH_AES_256_CBC_SHA384    0xC02A  /* 49194 */
/* RFC 5288 "AES Galois Counter Mode (GCM) Cipher Suites for TLS" */
#define TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 0xC02B  /*TLSv1.2 Kx=ECDH  Au=ECDSA Enc=AESGCM(128) Mac=AEAD */
#define TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 0xC02C  /*TLSv1.2 Kx=ECDH  Au=ECDSA Enc=AESGCM(256) Mac=AEAD */
#define TLS_ECDH_ECDSA_WITH_AES_128_GCM_SHA256  0xC02D  /* 49197 */
#define TLS_ECDH_ECDSA_WITH_AES_256_GCM_SHA384  0xC02E  /* 49198 */
#define TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256   0xC02F  /*TLSv1.2 Kx=ECDH  Au=RSA   Enc=AESGCM(128) Mac=AEAD */
#define TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384   0xC030  /*TLSv1.2 Kx=ECDH  Au=RSA   Enc=AESGCM(256) Mac=AEAD */
#define TLS_ECDH_RSA_WITH_AES_128_GCM_SHA256    0xC031  /* 49201 */
#define TLS_ECDH_RSA_WITH_AES_256_GCM_SHA384    0xC032  /* 49202 */
#define TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA      0xC035
#define TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA      0xC036
#define TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA256   0xC037
#define TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA384   0xC038

/* From http://wiki.mozilla.org/Security/Server_Side_TLS */
/* and 'openssl ciphers -V -stdname' */
#define TLS_RSA_WITH_AES_128_CCM                      0xC09C /*TLSv1.2 Kx=RSA   Au=RSA   Enc=AESCCM(128) Mac=AEAD */
#define TLS_RSA_WITH_AES_256_CCM                      0xC09D /*TLSv1.2 Kx=RSA   Au=RSA   Enc=AESCCM(256) Mac=AEAD */
#define TLS_DHE_RSA_WITH_AES_128_CCM                  0xC09E /*TLSv1.2 Kx=DH    Au=RSA   Enc=AESCCM(128) Mac=AEAD */
#define TLS_DHE_RSA_WITH_AES_256_CCM                  0xC09F /*TLSv1.2 Kx=DH    Au=RSA   Enc=AESCCM(256) Mac=AEAD */
#define TLS_RSA_WITH_AES_128_CCM_8                    0xC0A0 /*TLSv1.2 Kx=RSA   Au=RSA   Enc=AESCCM8(128) Mac=AEAD */
#define TLS_RSA_WITH_AES_256_CCM_8                    0xC0A1 /*TLSv1.2 Kx=RSA   Au=RSA   Enc=AESCCM8(256) Mac=AEAD */
#define TLS_DHE_RSA_WITH_AES_128_CCM_8                0xC0A2 /*TLSv1.2 Kx=DH    Au=RSA   Enc=AESCCM8(128) Mac=AEAD */
#define TLS_DHE_RSA_WITH_AES_256_CCM_8                0xC0A3 /*TLSv1.2 Kx=DH    Au=RSA   Enc=AESCCM8(256) Mac=AEAD */
#define TLS_ECDHE_ECDSA_WITH_AES_128_CCM              0xC0AC /*TLSv1.2 Kx=ECDH  Au=ECDSA Enc=AESCCM(128) Mac=AEAD */
#define TLS_ECDHE_ECDSA_WITH_AES_256_CCM              0xC0AD /*TLSv1.2 Kx=ECDH  Au=ECDSA Enc=AESCCM(256) Mac=AEAD */
#define TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8            0xC0AE /*TLSv1.2 Kx=ECDH  Au=ECDSA Enc=AESCCM8(128) Mac=AEAD */
#define TLS_ECDHE_ECDSA_WITH_AES_256_CCM_8            0xC0AF /*TLSv1.2 Kx=ECDH  Au=ECDSA Enc=AESCCM8(256) Mac=AEAD */
#define TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256   0xCCA8 /*TLSv1.2 Kx=ECDH  Au=RSA   Enc=CHACHA20/POLY1305(256) Mac=AEAD */
#define TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256 0xCCA9 /*TLSv1.2 Kx=ECDH  Au=ECDSA Enc=CHACHA20/POLY1305(256) Mac=AEAD */
#define TLS_DHE_RSA_WITH_CHACHA20_POLY1305_SHA256     0xCCAA /*TLSv1.2 Kx=DH    Au=RSA   Enc=CHACHA20/POLY1305(256) Mac=AEAD */

#define TLS_AES_128_GCM_SHA256                        0x1301 /*TLSv1.3 Kx=any   Au=any   Enc=AESGCM(128) Mac=AEAD */
#define TLS_AES_256_GCM_SHA384                        0x1302 /*TLSv1.3 Kx=any   Au=any   Enc=AESGCM(256) Mac=AEAD */
#define TLS_CHACHA20_POLY1305_SHA256                  0x1303 /*TLSv1.3 Kx=any   Au=any   Enc=CHACHA20/POLY1305(256) Mac=AEAD */
#define TLS_AES_128_CCM_SHA256                        0x1304 /*TLSv1.3 Kx=any   Au=any   Enc=AESCCM(128) Mac=AEAD */

/* Might go to libbb.h */
#define TLS_MAX_CRYPTBLOCK_SIZE 16
#define TLS_MAX_OUTBUF          (1 << 14)

enum {
        SHA_INSIZE     = 64,
        SHA1_OUTSIZE   = 20,
        SHA256_OUTSIZE = 32,

        AES128_KEYSIZE = 16,
        AES256_KEYSIZE = 32,

        RSA_PREMASTER_SIZE = 48,

        RECHDR_LEN = 5,

        /* 8 = 3+5. 3 extra bytes result in record data being 32-bit aligned */
        OUTBUF_PFX = 8 + AES_BLOCK_SIZE, /* header + IV */
        OUTBUF_SFX = TLS_MAX_MAC_SIZE + TLS_MAX_CRYPTBLOCK_SIZE, /* MAC + padding */

        // RFC 5246:
        // | 6.2.1. Fragmentation
        // |  The record layer fragments information blocks into TLSPlaintext
        // |  records carrying data in chunks of 2^14 bytes or less.  Client
        // |  message boundaries are not preserved in the record layer (i.e.,
        // |  multiple client messages of the same ContentType MAY be coalesced
        // |  into a single TLSPlaintext record, or a single message MAY be
        // |  fragmented across several records)
        // |...
        // |  length
        // |    The length (in bytes) of the following TLSPlaintext.fragment.
        // |    The length MUST NOT exceed 2^14.
        // |...
        // | 6.2.2. Record Compression and Decompression
        // |...
        // |  Compression must be lossless and may not increase the content length
        // |  by more than 1024 bytes.  If the decompression function encounters a
        // |  TLSCompressed.fragment that would decompress to a length in excess of
        // |  2^14 bytes, it MUST report a fatal decompression failure error.
        // |...
        // |  length
        // |    The length (in bytes) of the following TLSCompressed.fragment.
        // |    The length MUST NOT exceed 2^14 + 1024.
        // |...
        // | 6.2.3.  Record Payload Protection
        // |  The encryption and MAC functions translate a TLSCompressed
        // |  structure into a TLSCiphertext.  The decryption functions reverse
        // |  the process.  The MAC of the record also includes a sequence
        // |  number so that missing, extra, or repeated messages are
        // |  detectable.
        // |...
        // |  length
        // |    The length (in bytes) of the following TLSCiphertext.fragment.
        // |    The length MUST NOT exceed 2^14 + 2048.
        MAX_INBUF = RECHDR_LEN + (1 << 14) + 2048,

        /* Bits for tls->flags */
        NEED_EC_KEY            = 1 << 0,
        GOT_CERT_RSA_KEY_ALG   = 1 << 1,
        GOT_CERT_ECDSA_KEY_ALG = 1 << 2, // so far unused
        GOT_EC_KEY             = 1 << 3,
        ENCRYPTION_AESGCM      = 1 << 4, // else AES-SHA (or NULL-SHA if ALLOW_RSA_NULL_SHA256=1)
        ENCRYPT_ON_WRITE       = 1 << 5,
};

struct record_hdr {
        uint8_t type;
        uint8_t proto_maj, proto_min;
        uint8_t len16_hi, len16_lo;
};

struct tls_handshake_data {
        /* In bbox, md5/sha1/sha256 ctx's are the same structure */
        md5sha_ctx_t handshake_hash_ctx;

        uint8_t client_and_server_rand32[2 * 32];
        uint8_t master_secret[48];

//TODO: store just the DER key here, parse/use/delete it when sending client key
//this way it will stay key type agnostic here.
        psRsaKey_t server_rsa_pub_key;
        uint8_t ecc_pub_key32[32];

/* HANDSHAKE HASH: */
        //unsigned saved_client_hello_size;
        //uint8_t saved_client_hello[1];
};


static unsigned get24be(const uint8_t *p)
{
        return 0x100*(0x100*p[0] + p[1]) + p[2];
}

#if TLS_DEBUG
/* Nondestructively see the current hash value */
# if TLS_DEBUG_HASH
static unsigned sha_peek(md5sha_ctx_t *ctx, void *buffer)
{
        md5sha_ctx_t ctx_copy = *ctx; /* struct copy */
        return sha_end(&ctx_copy, buffer);
}
# endif

static void dump_hex(const char *fmt, const void *vp, int len)
{
        char hexbuf[32 * 1024 + 4];
        const uint8_t *p = vp;

        bin2hex(hexbuf, (void*)p, len)[0] = '\0';
        dbg(fmt, hexbuf);
}

static void dump_tls_record(const void *vp, int len)
{
        const uint8_t *p = vp;

        while (len > 0) {
                unsigned xhdr_len;
                if (len < RECHDR_LEN) {
                        dump_hex("< |%s|\n", p, len);
                        return;
                }
                xhdr_len = 0x100*p[3] + p[4];
                dbg("< hdr_type:%u ver:%u.%u len:%u", p[0], p[1], p[2], xhdr_len);
                p += RECHDR_LEN;
                len -= RECHDR_LEN;
                if (len >= 4 && p[-RECHDR_LEN] == RECORD_TYPE_HANDSHAKE) {
                        unsigned len24 = get24be(p + 1);
                        dbg(" type:%u len24:%u", p[0], len24);
                }
                if (xhdr_len > len)
                        xhdr_len = len;
                dump_hex(" |%s|\n", p, xhdr_len);
                p += xhdr_len;
                len -= xhdr_len;
        }
}
#else
# define dump_hex(...) ((void)0)
# define dump_tls_record(...) ((void)0)
#endif

void FAST_FUNC tls_get_random(void *buf, unsigned len)
{
        if (len != open_read_close("/dev/urandom", buf, len))
                xfunc_die();
}

static void xorbuf3(void *dst, const void *src1, const void *src2, unsigned count)
{
        uint8_t *d = dst;
        const uint8_t *s1 = src1;
        const uint8_t* s2 = src2;
        while (count--)
                *d++ = *s1++ ^ *s2++;
}

void FAST_FUNC xorbuf(void *dst, const void *src, unsigned count)
{
        xorbuf3(dst, dst, src, count);
}

void FAST_FUNC xorbuf_aligned_AES_BLOCK_SIZE(void *dst, const void *src)
{
        unsigned long *d = dst;
        const unsigned long *s = src;
        d[0] ^= s[0];
#if ULONG_MAX <= 0xffffffffffffffff
        d[1] ^= s[1];
 #if ULONG_MAX == 0xffffffff
        d[2] ^= s[2];
        d[3] ^= s[3];
 #endif
#endif
}

#if !TLS_DEBUG_HASH
# define hash_handshake(tls, fmt, buffer, len) \
         hash_handshake(tls, buffer, len)
#endif
static void hash_handshake(tls_state_t *tls, const char *fmt, const void *buffer, unsigned len)
{
        md5sha_hash(&tls->hsd->handshake_hash_ctx, buffer, len);
#if TLS_DEBUG_HASH
        {
                uint8_t h[TLS_MAX_MAC_SIZE];
                dump_hex(fmt, buffer, len);
                dbg(" (%u bytes) ", (int)len);
                len = sha_peek(&tls->hsd->handshake_hash_ctx, h);
                if (ENABLE_FEATURE_TLS_SHA1 && len == SHA1_OUTSIZE)
                        dump_hex("sha1:%s\n", h, len);
                else
                if (len == SHA256_OUTSIZE)
                        dump_hex("sha256:%s\n", h, len);
                else
                        dump_hex("sha???:%s\n", h, len);
        }
#endif
}

#if !ENABLE_FEATURE_TLS_SHA1
# define TLS_MAC_SIZE(tls) SHA256_OUTSIZE
#else
# define TLS_MAC_SIZE(tls) (tls)->MAC_size
#endif

// RFC 2104:
// HMAC(key, text) based on a hash H (say, sha256) is:
// ipad = [0x36 x INSIZE]
// opad = [0x5c x INSIZE]
// HMAC(key, text) = H((key XOR opad) + H((key XOR ipad) + text))
//
// H(key XOR opad) and H(key XOR ipad) can be precomputed
// if we often need HMAC hmac with the same key.
//
// text is often given in disjoint pieces.
typedef struct hmac_precomputed {
        md5sha_ctx_t hashed_key_xor_ipad;
        md5sha_ctx_t hashed_key_xor_opad;
} hmac_precomputed_t;

typedef void md5sha_begin_func(md5sha_ctx_t *ctx) FAST_FUNC;
#if !ENABLE_FEATURE_TLS_SHA1
#define hmac_begin(pre,key,key_size,begin) \
        hmac_begin(pre,key,key_size)
#define begin sha256_begin
#endif
static void hmac_begin(hmac_precomputed_t *pre, uint8_t *key, unsigned key_size, md5sha_begin_func *begin)
{
        uint8_t key_xor_ipad[SHA_INSIZE];
        uint8_t key_xor_opad[SHA_INSIZE];
//      uint8_t tempkey[SHA1_OUTSIZE < SHA256_OUTSIZE ? SHA256_OUTSIZE : SHA1_OUTSIZE];
        unsigned i;

        // "The authentication key can be of any length up to INSIZE, the
        // block length of the hash function.  Applications that use keys longer
        // than INSIZE bytes will first hash the key using H and then use the
        // resultant OUTSIZE byte string as the actual key to HMAC."
        if (key_size > SHA_INSIZE) {
                bb_error_msg_and_die("HMAC key>64"); //does not happen (yet?)
//              md5sha_ctx_t ctx;
//              begin(&ctx);
//              md5sha_hash(&ctx, key, key_size);
//              key_size = sha_end(&ctx, tempkey);
//              //key = tempkey; - right? RIGHT? why does it work without this?
//              // because SHA_INSIZE is 64, but hmac() is always called with
//              // key_size = tls->MAC_size = SHA1/256_OUTSIZE (20 or 32),
//              // and prf_hmac_sha256() -> hmac_sha256() key sizes are:
//              // - RSA_PREMASTER_SIZE is 48
//              // - CURVE25519_KEYSIZE is 32
//              // - master_secret[] is 48
        }

        for (i = 0; i < key_size; i++) {
                key_xor_ipad[i] = key[i] ^ 0x36;
                key_xor_opad[i] = key[i] ^ 0x5c;
        }
        for (; i < SHA_INSIZE; i++) {
                key_xor_ipad[i] = 0x36;
                key_xor_opad[i] = 0x5c;
        }

        begin(&pre->hashed_key_xor_ipad);
        begin(&pre->hashed_key_xor_opad);
        md5sha_hash(&pre->hashed_key_xor_ipad, key_xor_ipad, SHA_INSIZE);
        md5sha_hash(&pre->hashed_key_xor_opad, key_xor_opad, SHA_INSIZE);
}
#undef begin

static unsigned hmac_sha_precomputed_v(
                hmac_precomputed_t *pre,
                uint8_t *out,
                va_list va)
{
        uint8_t *text;
        unsigned len;

        /* pre->hashed_key_xor_ipad contains unclosed "H((key XOR ipad) +" state */
        /* pre->hashed_key_xor_opad contains unclosed "H((key XOR opad) +" state */

        /* calculate out = H((key XOR ipad) + text) */
        while ((text = va_arg(va, uint8_t*)) != NULL) {
                unsigned text_size = va_arg(va, unsigned);
                md5sha_hash(&pre->hashed_key_xor_ipad, text, text_size);
        }
        len = sha_end(&pre->hashed_key_xor_ipad, out);

        /* out = H((key XOR opad) + out) */
        md5sha_hash(&pre->hashed_key_xor_opad, out, len);
        return sha_end(&pre->hashed_key_xor_opad, out);
}

static unsigned hmac_sha_precomputed(hmac_precomputed_t *pre_init, uint8_t *out, ...)
{
        hmac_precomputed_t pre;
        va_list va;
        unsigned len;

        va_start(va, out);
        pre = *pre_init; /* struct copy */
        len = hmac_sha_precomputed_v(&pre, out, va);
        va_end(va);
        return len;
}

#if !ENABLE_FEATURE_TLS_SHA1
#define hmac(tls,out,key,key_size,...) \
        hmac(out,key,key_size, __VA_ARGS__)
#endif
static unsigned hmac(tls_state_t *tls, uint8_t *out, uint8_t *key, unsigned key_size, ...)
{
        hmac_precomputed_t pre;
        va_list va;
        unsigned len;

        va_start(va, key_size);

        hmac_begin(&pre, key, key_size,
                        (ENABLE_FEATURE_TLS_SHA1 && tls->MAC_size == SHA1_OUTSIZE)
                                ? sha1_begin
                                : sha256_begin
        );
        len = hmac_sha_precomputed_v(&pre, out, va);

        va_end(va);
        return len;
}

// RFC 5246:
// 5.  HMAC and the Pseudorandom Function
//...
// In this section, we define one PRF, based on HMAC.  This PRF with the
// SHA-256 hash function is used for all cipher suites defined in this
// document and in TLS documents published prior to this document when
// TLS 1.2 is negotiated.
// ^^^^^^^^^^^^^ IMPORTANT!
//               PRF uses sha256 regardless of cipher for all ciphers
//               defined by RFC 5246. It's not sha1 for AES_128_CBC_SHA!
//               However, for _SHA384 ciphers, it's sha384. See RFC 5288,5289.
//...
//    P_hash(secret, seed) = HMAC_hash(secret, A(1) + seed) +
//                           HMAC_hash(secret, A(2) + seed) +
//                           HMAC_hash(secret, A(3) + seed) + ...
// where + indicates concatenation.
// A() is defined as:
//    A(0) = seed
//    A(1) = HMAC_hash(secret, A(0)) = HMAC_hash(secret, seed)
//    A(i) = HMAC_hash(secret, A(i-1))
// P_hash can be iterated as many times as necessary to produce the
// required quantity of data.  For example, if P_SHA256 is being used to
// create 80 bytes of data, it will have to be iterated three times
// (through A(3)), creating 96 bytes of output data; the last 16 bytes
// of the final iteration will then be discarded, leaving 80 bytes of
// output data.
//
// TLS's PRF is created by applying P_hash to the secret as:
//
//    PRF(secret, label, seed) = P_<hash>(secret, label + seed)
//
// The label is an ASCII string.
//
// RFC 5288:
// For cipher suites ending with _SHA256, the PRF is the TLS PRF
// with SHA-256 as the hash function.
// For cipher suites ending with _SHA384, the PRF is the TLS PRF
// with SHA-384 as the hash function.
static void prf_hmac_sha256(/*tls_state_t *tls,*/
                uint8_t *outbuf, unsigned outbuf_size,
                uint8_t *secret, unsigned secret_size,
                const char *label,
                uint8_t *seed, unsigned seed_size)
{
        hmac_precomputed_t pre;
        uint8_t a[TLS_MAX_MAC_SIZE];
        uint8_t *out_p = outbuf;
        unsigned label_size = strlen(label);
        unsigned MAC_size = SHA256_OUTSIZE;

        /* In P_hash() calculation, "seed" is "label + seed": */
#define SEED   label, label_size, seed, seed_size
#define A      a, MAC_size

        hmac_begin(&pre, secret, secret_size, sha256_begin);

        /* A(1) = HMAC_hash(secret, seed) */
        hmac_sha_precomputed(&pre, a, SEED, NULL);

        for (;;) {
                /* HMAC_hash(secret, A(1) + seed) */
                if (outbuf_size <= MAC_size) {
                        /* Last, possibly incomplete, block */
                        /* (use a[] as temp buffer) */
                        hmac_sha_precomputed(&pre, a, A, SEED, NULL);
                        memcpy(out_p, a, outbuf_size);
                        return;
                }
                /* Not last block. Store directly to result buffer */
                hmac_sha_precomputed(&pre, out_p, A, SEED, NULL);
                out_p += MAC_size;
                outbuf_size -= MAC_size;
                /* A(2) = HMAC_hash(secret, A(1)) */
                hmac_sha_precomputed(&pre, a, A, NULL);
        }
#undef A
#undef SECRET
#undef SEED
}

static void bad_record_die(tls_state_t *tls, const char *expected, int len)
{
        bb_error_msg("got bad TLS record (len:%d) while expecting %s", len, expected);
        if (len > 0) {
                uint8_t *p = tls->inbuf;
                if (len > 99)
                        len = 99; /* don't flood, a few lines should be enough */
                do {
                        fprintf(stderr, " %02x", *p++);
                        len--;
                } while (len != 0);
                fputc('\n', stderr);
        }
        xfunc_die();
}

static void tls_error_die(tls_state_t *tls, int line)
{
        dump_tls_record(tls->inbuf, tls->ofs_to_buffered + tls->buffered_size);
        bb_error_msg_and_die("tls error at line %d cipher:%04x", line, tls->cipher_id);
}
#define tls_error_die(tls) tls_error_die(tls, __LINE__)

#if 0 //UNUSED
static void tls_free_inbuf(tls_state_t *tls)
{
        if (tls->buffered_size == 0) {
                free(tls->inbuf);
                tls->inbuf_size = 0;
                tls->inbuf = NULL;
        }
}
#endif

static void tls_free_outbuf(tls_state_t *tls)
{
        free(tls->outbuf);
        tls->outbuf_size = 0;
        tls->outbuf = NULL;
}

static void *tls_get_outbuf(tls_state_t *tls, int len)
{
        if (len > TLS_MAX_OUTBUF)
                xfunc_die();
        len += OUTBUF_PFX + OUTBUF_SFX;
        if (tls->outbuf_size < len) {
                tls->outbuf_size = len;
                tls->outbuf = xrealloc(tls->outbuf, len);
        }
        return tls->outbuf + OUTBUF_PFX;
}

static void *tls_get_zeroed_outbuf(tls_state_t *tls, int len)
{
        void *record = tls_get_outbuf(tls, len);
        memset(record, 0, len);
        return record;
}

static void xwrite_encrypted_and_hmac_signed(tls_state_t *tls, unsigned size, unsigned type)
{
        uint8_t *buf = tls->outbuf + OUTBUF_PFX;
        struct record_hdr *xhdr;
        uint8_t padding_length;

        xhdr = (void*)(buf - RECHDR_LEN);
        if (!ALLOW_RSA_NULL_SHA256 /* if "no encryption" can't be selected */
         || tls->cipher_id != TLS_RSA_WITH_NULL_SHA256 /* or if it wasn't selected */
        ) {
                xhdr = (void*)(buf - RECHDR_LEN - AES_BLOCK_SIZE); /* place for IV */
        }

        xhdr->type = type;
        xhdr->proto_maj = TLS_MAJ;
        xhdr->proto_min = TLS_MIN;
        /* fake unencrypted record len for MAC calculation */
        xhdr->len16_hi = size >> 8;
        xhdr->len16_lo = size & 0xff;

        /* Calculate MAC signature */
        hmac(tls, buf + size, /* result */
                tls->client_write_MAC_key, TLS_MAC_SIZE(tls),
                &tls->write_seq64_be, sizeof(tls->write_seq64_be),
                xhdr, RECHDR_LEN,
                buf, size,
                NULL
        );
        tls->write_seq64_be = SWAP_BE64(1 + SWAP_BE64(tls->write_seq64_be));

        size += TLS_MAC_SIZE(tls);

        // RFC 5246:
        // 6.2.3.1.  Null or Standard Stream Cipher
        //
        // Stream ciphers (including BulkCipherAlgorithm.null; see Appendix A.6)
        // convert TLSCompressed.fragment structures to and from stream
        // TLSCiphertext.fragment structures.
        //
        //    stream-ciphered struct {
        //        opaque content[TLSCompressed.length];
        //        opaque MAC[SecurityParameters.mac_length];
        //    } GenericStreamCipher;
        //
        // The MAC is generated as:
        //    MAC(MAC_write_key, seq_num +
        //                          TLSCompressed.type +
        //                          TLSCompressed.version +
        //                          TLSCompressed.length +
        //                          TLSCompressed.fragment);
        // where "+" denotes concatenation.
        // seq_num
        //    The sequence number for this record.
        // MAC
        //    The MAC algorithm specified by SecurityParameters.mac_algorithm.
        //
        // Note that the MAC is computed before encryption.  The stream cipher
        // encrypts the entire block, including the MAC.
        //...
        // Appendix C.  Cipher Suite Definitions
        //...
        // MAC       Algorithm    mac_length  mac_key_length
        // --------  -----------  ----------  --------------
        // SHA       HMAC-SHA1       20            20
        // SHA256    HMAC-SHA256     32            32
        if (ALLOW_RSA_NULL_SHA256
         && tls->cipher_id == TLS_RSA_WITH_NULL_SHA256
        ) {
                /* No encryption, only signing */
                xhdr->len16_hi = size >> 8;
                xhdr->len16_lo = size & 0xff;
                dump_raw_out(">> %s\n", xhdr, RECHDR_LEN + size);
                xwrite(tls->ofd, xhdr, RECHDR_LEN + size);
                dbg("wrote %u bytes (NULL crypt, SHA256 hash)\n", size);
                return;
        }

        // 6.2.3.2.  CBC Block Cipher
        // For block ciphers (such as 3DES or AES), the encryption and MAC
        // functions convert TLSCompressed.fragment structures to and from block
        // TLSCiphertext.fragment structures.
        //    struct {
        //        opaque IV[SecurityParameters.record_iv_length];
        //        block-ciphered struct {
        //            opaque content[TLSCompressed.length];
        //            opaque MAC[SecurityParameters.mac_length];
        //            uint8 padding[GenericBlockCipher.padding_length];
        //            uint8 padding_length;
        //        };
        //    } GenericBlockCipher;
        //...
        // IV
        //    The Initialization Vector (IV) SHOULD be chosen at random, and
        //    MUST be unpredictable.  Note that in versions of TLS prior to 1.1,
        //    there was no IV field (...).  For block ciphers, the IV length is
        //    of length SecurityParameters.record_iv_length, which is equal to the
        //    SecurityParameters.block_size.
        // padding
        //    Padding that is added to force the length of the plaintext to be
        //    an integral multiple of the block cipher's block length.
        // padding_length
        //    The padding length MUST be such that the total size of the
        //    GenericBlockCipher structure is a multiple of the cipher's block
        //    length.  Legal values range from zero to 255, inclusive.
        //...
        // Appendix C.  Cipher Suite Definitions
        //...
        //                         Key      IV   Block
        // Cipher        Type    Material  Size  Size
        // ------------  ------  --------  ----  -----
        // AES_128_CBC   Block      16      16     16
        // AES_256_CBC   Block      32      16     16

        tls_get_random(buf - AES_BLOCK_SIZE, AES_BLOCK_SIZE); /* IV */
        dbg("before crypt: 5 hdr + %u data + %u hash bytes\n",
                        size - TLS_MAC_SIZE(tls), TLS_MAC_SIZE(tls));

        /* Fill IV and padding in outbuf */
        // RFC is talking nonsense:
        //    "Padding that is added to force the length of the plaintext to be
        //    an integral multiple of the block cipher's block length."
        // WRONG. _padding+padding_length_, not just _padding_,
        // pads the data.
        // IOW: padding_length is the last byte of padding[] array,
        // contrary to what RFC depicts.
        //
        // What actually happens is that there is always padding.
        // If you need one byte to reach BLOCKSIZE, this byte is 0x00.
        // If you need two bytes, they are both 0x01.
        // If you need three, they are 0x02,0x02,0x02. And so on.
        // If you need no bytes to reach BLOCKSIZE, you have to pad a full
        // BLOCKSIZE with bytes of value (BLOCKSIZE-1).
        // It's ok to have more than minimum padding, but we do minimum.
        padding_length = (~size) & (AES_BLOCK_SIZE - 1);
        do {
                buf[size++] = padding_length; /* padding */
        } while ((size & (AES_BLOCK_SIZE - 1)) != 0);

        /* Encrypt content+MAC+padding in place */
        aes_cbc_encrypt(
                &tls->aes_encrypt, /* selects 128/256 */
                buf - AES_BLOCK_SIZE, /* IV */
                buf, size, /* plaintext */
                buf /* ciphertext */
        );

        /* Write out */
        dbg("writing 5 + %u IV + %u encrypted bytes, padding_length:0x%02x\n",
                        AES_BLOCK_SIZE, size, padding_length);
        size += AES_BLOCK_SIZE;     /* + IV */
        xhdr->len16_hi = size >> 8;
        xhdr->len16_lo = size & 0xff;
        dump_raw_out(">> %s\n", xhdr, RECHDR_LEN + size);
        xwrite(tls->ofd, xhdr, RECHDR_LEN + size);
        dbg("wrote %u bytes\n", (int)RECHDR_LEN + size);
}

/* Example how GCM encryption combines nonce, aad, input and generates
 * "header | exp_nonce | encrypted output | tag":
 * nonce:0d 6a 26 31 00 00 00 00 00 00 00 01 (implicit 4 bytes (derived from master secret), then explicit 8 bytes)
 * aad:  00 00 00 00 00 00 00 01 17 03 03 00 1c
 * in:   47 45 54 20 2f 69 6e 64 65 78 2e 68 74 6d 6c 20 48 54 54 50 2f 31 2e 30 0d 0a 0d 0a "GET /index.html HTTP/1.0\r\n\r\n" (0x1c bytes)
 * out:  f7 8a b2 8f 78 0e f6 d5 76 17 2e b5 6d 46 59 56 8b 46 9f 0b d9 2c 35 28 13 66 19 be
 * tag:  c2 86 ce 4a 50 4a d0 aa 50 b3 76 5c 49 2a 3f 33
 * sent: 17 03 03 00 34|00 00 00 00 00 00 00 01|f7 8a b2 8f 78 0e f6 d5 76 17 2e b5 6d 46 59 56 8b 46 9f 0b d9 2c 35 28 13 66 19 be|c2 86 ce 4a 50 4a d0 aa 50 b3 76 5c 49 2a 3f 33
 * .............................................^^ buf points here
 */
static void xwrite_encrypted_aesgcm(tls_state_t *tls, unsigned size, unsigned type)
{
#define COUNTER(v) (*(uint32_t*)(v + 12))

        uint8_t aad[13 + 3] ALIGNED_long;   /* +3 creates [16] buffer, simplifying GHASH() */
        uint8_t nonce[12 + 4] ALIGNED_long; /* +4 creates space for AES block counter */
        uint8_t scratch[AES_BLOCK_SIZE] ALIGNED_long; //[16]
        uint8_t authtag[AES_BLOCK_SIZE] ALIGNED_long; //[16]
        uint8_t *buf;
        struct record_hdr *xhdr;
        unsigned remaining;
        unsigned cnt;
        uint64_t t64;

        buf = tls->outbuf + OUTBUF_PFX; /* see above for the byte it points to */
        dump_hex("xwrite_encrypted_aesgcm plaintext:%s\n", buf, size);

        xhdr = (void*)(buf - 8 - RECHDR_LEN);
        xhdr->type = type; /* do it here so that "type" param no longer used */

        aad[8] = type;
        aad[9] = TLS_MAJ;
        aad[10] = TLS_MIN;
        aad[11] = size >> 8;
        /* set aad[12], and clear aad[13..15] */
        COUNTER(aad) = SWAP_LE32(size & 0xff);

        memcpy(nonce, tls->client_write_IV, 4);
        t64 = tls->write_seq64_be;
        move_to_unaligned64(nonce + 4, t64);
        move_to_unaligned64(aad,       t64);
        move_to_unaligned64(buf - 8,   t64);
        /* seq64 is not used later in this func, can increment here */
        tls->write_seq64_be = SWAP_BE64(1 + SWAP_BE64(t64));

        cnt = 1;
        remaining = size;
        while (remaining != 0) {
                unsigned n;

                cnt++;
                COUNTER(nonce) = htonl(cnt); /* yes, first cnt here is 2 (!) */
                aes_encrypt_one_block(&tls->aes_encrypt, nonce, scratch);
                n = remaining > AES_BLOCK_SIZE ? AES_BLOCK_SIZE : remaining;
                xorbuf(buf, scratch, n);
                buf += n;
                remaining -= n;
        }

        aesgcm_GHASH(tls->H, aad, /*sizeof(aad),*/ tls->outbuf + OUTBUF_PFX, size, authtag /*, sizeof(authtag)*/);
        COUNTER(nonce) = htonl(1);
        aes_encrypt_one_block(&tls->aes_encrypt, nonce, scratch);
        xorbuf_aligned_AES_BLOCK_SIZE(authtag, scratch);

        memcpy(buf, authtag, sizeof(authtag));

        /* Write out */
        xhdr = (void*)(tls->outbuf + OUTBUF_PFX - 8 - RECHDR_LEN);
        size += 8 + sizeof(authtag);
        /*xhdr->type = type; - already is */
        xhdr->proto_maj = TLS_MAJ;
        xhdr->proto_min = TLS_MIN;
        xhdr->len16_hi = size >> 8;
        xhdr->len16_lo = size & 0xff;
        size += RECHDR_LEN;
        dump_raw_out(">> %s\n", xhdr, size);
        xwrite(tls->ofd, xhdr, size);
        dbg("wrote %u bytes\n", size);
#undef COUNTER
}

static void xwrite_encrypted(tls_state_t *tls, unsigned size, unsigned type)
{
        if (!(tls->flags & ENCRYPTION_AESGCM)) {
                xwrite_encrypted_and_hmac_signed(tls, size, type);
                return;
        }
        xwrite_encrypted_aesgcm(tls, size, type);
}

static void xwrite_handshake_record(tls_state_t *tls, unsigned size)
{
        uint8_t *buf = tls->outbuf + OUTBUF_PFX;
        struct record_hdr *xhdr = (void*)(buf - RECHDR_LEN);

        xhdr->type = RECORD_TYPE_HANDSHAKE;
        xhdr->proto_maj = TLS_MAJ;
        xhdr->proto_min = TLS_MIN;
        xhdr->len16_hi = size >> 8;
        xhdr->len16_lo = size & 0xff;
        dump_raw_out(">> %s\n", xhdr, RECHDR_LEN + size);
        xwrite(tls->ofd, xhdr, RECHDR_LEN + size);
        dbg("wrote %u bytes\n", (int)RECHDR_LEN + size);
}

static void xwrite_and_update_handshake_hash(tls_state_t *tls, unsigned size)
{
        if (!(tls->flags & ENCRYPT_ON_WRITE)) {
                uint8_t *buf;

                xwrite_handshake_record(tls, size);
                /* Handshake hash does not include record headers */
                buf = tls->outbuf + OUTBUF_PFX;
                hash_handshake(tls, ">> hash:%s", buf, size);
                return;
        }
        xwrite_encrypted(tls, size, RECORD_TYPE_HANDSHAKE);
}

static int tls_has_buffered_record(tls_state_t *tls)
{
        int buffered = tls->buffered_size;
        struct record_hdr *xhdr;
        int rec_size;

        if (buffered < RECHDR_LEN)
                return 0;
        xhdr = (void*)(tls->inbuf + tls->ofs_to_buffered);
        rec_size = RECHDR_LEN + (0x100 * xhdr->len16_hi + xhdr->len16_lo);
        if (buffered < rec_size)
                return 0;
        return rec_size;
}

static const char *alert_text(int code)
{
        switch (code) {
        case 20:  return "bad MAC";
        case 50:  return "decode error";
        case 51:  return "decrypt error";
        case 40:  return "handshake failure";
        case 112: return "unrecognized name";
        }
        return itoa(code);
}

static void tls_aesgcm_decrypt(tls_state_t *tls, uint8_t *buf, int size)
{
#define COUNTER(v) (*(uint32_t*)(v + 12))

        //uint8_t aad[13 + 3] ALIGNED_long; /* +3 creates [16] buffer, simplifying GHASH() */
        uint8_t nonce[12 + 4] ALIGNED_long; /* +4 creates space for AES block counter */
        uint8_t scratch[AES_BLOCK_SIZE] ALIGNED_long; //[16]
        //uint8_t authtag[AES_BLOCK_SIZE] ALIGNED_long; //[16]
        unsigned remaining;
        unsigned cnt;

        //memcpy(aad, buf, 8);
        //aad[8] = type;
        //aad[9] = TLS_MAJ;
        //aad[10] = TLS_MIN;
        //aad[11] = size >> 8;
        ///* set aad[12], and clear aad[13..15] */
        //COUNTER(aad) = SWAP_LE32(size & 0xff);

        memcpy(nonce,     tls->server_write_IV, 4);

        memcpy(nonce + 4, buf, 8);

        cnt = 1;
        remaining = size;
        while (remaining != 0) {
                unsigned n;

                cnt++;
                COUNTER(nonce) = htonl(cnt); /* yes, first cnt here is 2 (!) */
                aes_encrypt_one_block(&tls->aes_decrypt, nonce, scratch);
                n = remaining > AES_BLOCK_SIZE ? AES_BLOCK_SIZE : remaining;
                xorbuf3(buf, scratch, buf + 8, n);
                buf += n;
                remaining -= n;
        }

        //aesgcm_GHASH(tls->H, aad, tls->inbuf + RECHDR_LEN, size, authtag);
        //COUNTER(nonce) = htonl(1);
        //aes_encrypt_one_block(&tls->aes_encrypt, nonce, scratch);
        //xorbuf_aligned_AES_BLOCK_SIZE(authtag, scratch);

        //memcmp(buf, authtag, sizeof(authtag)) || DIE("HASH DOES NOT MATCH!");
#undef COUNTER
}

static int tls_xread_record(tls_state_t *tls, const char *expected)
{
        struct record_hdr *xhdr;
        int sz;
        int total;
        int target;

 again:
        dbg("ofs_to_buffered:%u buffered_size:%u\n", tls->ofs_to_buffered, tls->buffered_size);
        total = tls->buffered_size;
        if (total != 0) {
                memmove(tls->inbuf, tls->inbuf + tls->ofs_to_buffered, total);
                //dbg("<< remaining at %d [%d] ", tls->ofs_to_buffered, total);
                //dump_raw_in("<< %s\n", tls->inbuf, total);
        }
        errno = 0;
        target = MAX_INBUF;
        for (;;) {
                int rem;

                if (total >= RECHDR_LEN && target == MAX_INBUF) {
                        xhdr = (void*)tls->inbuf;
                        target = RECHDR_LEN + (0x100 * xhdr->len16_hi + xhdr->len16_lo);

                        if (target > MAX_INBUF /* malformed input (too long) */
                         || xhdr->proto_maj != TLS_MAJ
                         || xhdr->proto_min != TLS_MIN
                        ) {
                                sz = total < target ? total : target;
                                bad_record_die(tls, expected, sz);
                        }
                        dbg("xhdr type:%d ver:%d.%d len:%d\n",
                                xhdr->type, xhdr->proto_maj, xhdr->proto_min,
                                0x100 * xhdr->len16_hi + xhdr->len16_lo
                        );
                }
                /* if total >= target, we have a full packet (and possibly more)... */
                if (total - target >= 0)
                        break;
                /* input buffer is grown only as needed */
                rem = tls->inbuf_size - total;
                if (rem == 0) {
                        tls->inbuf_size += MAX_INBUF / 8;
                        if (tls->inbuf_size > MAX_INBUF)
                                tls->inbuf_size = MAX_INBUF;
                        dbg("inbuf_size:%d\n", tls->inbuf_size);
                        rem = tls->inbuf_size - total;
                        tls->inbuf = xrealloc(tls->inbuf, tls->inbuf_size);
                }
                sz = safe_read(tls->ifd, tls->inbuf + total, rem);
                if (sz <= 0) {
                        if (sz == 0 && total == 0) {
                                /* "Abrupt" EOF, no TLS shutdown (seen from kernel.org) */
                                dbg("EOF (without TLS shutdown) from peer\n");
                                tls->buffered_size = 0;
                                goto end;
                        }
                        bb_perror_msg_and_die("short read, have only %d", total);
                }
                dump_raw_in("<< %s\n", tls->inbuf + total, sz);
                total += sz;
        }
        tls->buffered_size = total - target;
        tls->ofs_to_buffered = target;
        //dbg("<< stashing at %d [%d] ", tls->ofs_to_buffered, tls->buffered_size);
        //dump_hex("<< %s\n", tls->inbuf + tls->ofs_to_buffered, tls->buffered_size);

        sz = target - RECHDR_LEN;

        /* Needs to be decrypted? */
        if (tls->min_encrypted_len_on_read != 0) {
                if (sz < (int)tls->min_encrypted_len_on_read)
                        bb_error_msg_and_die("bad encrypted len:%u", sz);

                if (tls->flags & ENCRYPTION_AESGCM) {
                        /* AESGCM */
                        uint8_t *p = tls->inbuf + RECHDR_LEN;

                        sz -= 8 + AES_BLOCK_SIZE; /* we will overwrite nonce, drop hash */
                        tls_aesgcm_decrypt(tls, p, sz);
                        dbg("encrypted size:%u\n", sz);
                } else
                if (tls->min_encrypted_len_on_read > TLS_MAC_SIZE(tls)) {
                        /* AES+SHA */
                        uint8_t *p = tls->inbuf + RECHDR_LEN;
                        int padding_len;

                        if (sz & (AES_BLOCK_SIZE-1))
                                bb_error_msg_and_die("bad encrypted len:%u", sz);

                        /* Decrypt content+MAC+padding, moving it over IV in the process */
                        sz -= AES_BLOCK_SIZE; /* we will overwrite IV now */
                        aes_cbc_decrypt(
                                &tls->aes_decrypt, /* selects 128/256 */
                                p, /* IV */
                                p + AES_BLOCK_SIZE, sz, /* ciphertext */
                                p /* plaintext */
                        );
                        padding_len = p[sz - 1];
                        dbg("encrypted size:%u type:0x%02x padding_length:0x%02x\n", sz, p[0], padding_len);
                        padding_len++;
                        sz -= TLS_MAC_SIZE(tls) + padding_len; /* drop MAC and padding */
                } else {
                        /* if nonzero, then it's TLS_RSA_WITH_NULL_SHA256: drop MAC */
                        /* else: no encryption yet on input, subtract zero = NOP */
                        sz -= tls->min_encrypted_len_on_read;
                }
        }
        if (sz < 0)
                bb_error_msg_and_die("encrypted data too short");

        //dump_hex("<< %s\n", tls->inbuf, RECHDR_LEN + sz);

        xhdr = (void*)tls->inbuf;
        if (xhdr->type == RECORD_TYPE_ALERT && sz >= 2) {
                uint8_t *p = tls->inbuf + RECHDR_LEN;
                dbg("ALERT size:%d level:%d description:%d\n", sz, p[0], p[1]);
                if (p[0] == 2) { /* fatal */
                        bb_error_msg_and_die("TLS %s from peer (alert code %d): %s",
                                "error",
                                p[1], alert_text(p[1])
                        );
                }
                if (p[0] == 1) { /* warning */
                        if (p[1] == 0) { /* "close_notify" warning: it's EOF */
                                dbg("EOF (TLS encoded) from peer\n");
                                sz = 0;
                                goto end;
                        }
//This possibly needs to be cached and shown only if
//a fatal alert follows
//                      bb_error_msg("TLS %s from peer (alert code %d): %s",
//                              "warning",
//                              p[1], alert_text(p[1])
//                      );
                        /* discard it, get next record */
                        goto again;
                }
                /* p[0] not 1 or 2: not defined in protocol */
                sz = 0;
                goto end;
        }

        /* RFC 5246 is not saying it explicitly, but sha256 hash
         * in our FINISHED record must include data of incoming packets too!
         */
        if (tls->inbuf[0] == RECORD_TYPE_HANDSHAKE
/* HANDSHAKE HASH: */
        // && do_we_know_which_hash_to_use /* server_hello() might not know it in the future! */
        ) {
                hash_handshake(tls, "<< hash:%s", tls->inbuf + RECHDR_LEN, sz);
        }
 end:
        dbg("got block len:%u\n", sz);
        return sz;
}

static void binary_to_pstm(pstm_int *pstm_n, uint8_t *bin_ptr, unsigned len)
{
        pstm_init_for_read_unsigned_bin(/*pool:*/ NULL, pstm_n, len);
        pstm_read_unsigned_bin(pstm_n, bin_ptr, len);
        //return bin_ptr + len;
}

/*
 * DER parsing routines
 */
static unsigned get_der_len(uint8_t **bodyp, uint8_t *der, uint8_t *end)
{
        unsigned len, len1;

        if (end - der < 2)
                xfunc_die();
//      if ((der[0] & 0x1f) == 0x1f) /* not single-byte item code? */
//              xfunc_die();

        len = der[1]; /* maybe it's short len */
        if (len >= 0x80) {
                /* no, it's long */

                if (len == 0x80 || end - der < (int)(len - 0x7e)) {
                        /* 0x80 is "0 bytes of len", invalid DER: must use short len if can */
                        /* need 3 or 4 bytes for 81, 82 */
                        xfunc_die();
                }

                len1 = der[2]; /* if (len == 0x81) it's "ii 81 xx", fetch xx */
                if (len > 0x82) {
                        /* >0x82 is "3+ bytes of len", should not happen realistically */
                        xfunc_die();
                }
                if (len == 0x82) { /* it's "ii 82 xx yy" */
                        len1 = 0x100*len1 + der[3];
                        der += 1; /* skip [yy] */
                }
                der += 1; /* skip [xx] */
                len = len1;
//              if (len < 0x80)
//                      xfunc_die(); /* invalid DER: must use short len if can */
        }
        der += 2; /* skip [code]+[1byte] */

        if (end - der < (int)len)
                xfunc_die();
        *bodyp = der;

        return len;
}

static uint8_t *enter_der_item(uint8_t *der, uint8_t **endp)
{
        uint8_t *new_der;
        unsigned len = get_der_len(&new_der, der, *endp);
        dbg_der("entered der @%p:0x%02x len:%u inner_byte @%p:0x%02x\n", der, der[0], len, new_der, new_der[0]);
        /* Move "end" position to cover only this item */
        *endp = new_der + len;
        return new_der;
}

static uint8_t *skip_der_item(uint8_t *der, uint8_t *end)
{
        uint8_t *new_der;
        unsigned len = get_der_len(&new_der, der, end);
        /* Skip body */
        new_der += len;
        dbg_der("skipped der 0x%02x, next byte 0x%02x\n", der[0], new_der[0]);
        return new_der;
}

static void der_binary_to_pstm(pstm_int *pstm_n, uint8_t *der, uint8_t *end)
{
        uint8_t *bin_ptr;
        unsigned len = get_der_len(&bin_ptr, der, end);

        dbg_der("binary bytes:%u, first:0x%02x\n", len, bin_ptr[0]);
        binary_to_pstm(pstm_n, bin_ptr, len);
}

static void find_key_in_der_cert(tls_state_t *tls, uint8_t *der, int len)
{
/* Certificate is a DER-encoded data structure. Each DER element has a length,
 * which makes it easy to skip over large compound elements of any complexity
 * without parsing them. Example: partial decode of kernel.org certificate:
 *  SEQ 0x05ac/1452 bytes (Certificate): 308205ac
 *    SEQ 0x0494/1172 bytes (tbsCertificate): 30820494
 *      [ASN_CONTEXT_SPECIFIC | ASN_CONSTRUCTED | 0] 3 bytes: a003
 *        INTEGER (version): 0201 02
 *      INTEGER 0x11 bytes (serialNumber): 0211 00 9f85bf664b0cddafca508679501b2be4
 *      //^^^^^^note: matrixSSL also allows [ASN_CONTEXT_SPECIFIC | ASN_PRIMITIVE | 2] = 0x82 type
 *      SEQ 0x0d bytes (signatureAlgo): 300d
 *        OID 9 bytes: 0609 2a864886f70d01010b (OID_SHA256_RSA_SIG 42.134.72.134.247.13.1.1.11)
 *        NULL: 0500
 *      SEQ 0x5f bytes (issuer): 305f
 *        SET 11 bytes: 310b
 *          SEQ 9 bytes: 3009
 *            OID 3 bytes: 0603 550406
 *            Printable string "FR": 1302 4652
 *        SET 14 bytes: 310e
 *          SEQ 12 bytes: 300c
 *            OID 3 bytes: 0603 550408
 *            Printable string "Paris": 1305 5061726973
 *        SET 14 bytes: 310e
 *          SEQ 12 bytes: 300c
 *            OID 3 bytes: 0603 550407
 *            Printable string "Paris": 1305 5061726973
 *        SET 14 bytes: 310e
 *          SEQ 12 bytes: 300c
 *            OID 3 bytes: 0603 55040a
 *            Printable string "Gandi": 1305 47616e6469
 *        SET 32 bytes: 3120
 *          SEQ 30 bytes: 301e
 *            OID 3 bytes: 0603 550403
 *            Printable string "Gandi Standard SSL CA 2": 1317 47616e6469205374616e646172642053534c2043412032
 *      SEQ 30 bytes (validity): 301e
 *        TIME "161011000000Z": 170d 3136313031313030303030305a
 *        TIME "191011235959Z": 170d 3139313031313233353935395a
 *      SEQ 0x5b/91 bytes (subject): 305b //I did not decode this
 *          3121301f060355040b1318446f6d61696e20436f
 *          6e74726f6c2056616c6964617465643121301f06
 *          0355040b1318506f73697469766553534c204d75
 *          6c74692d446f6d61696e31133011060355040313
 *          0a6b65726e656c2e6f7267
 *      SEQ 0x01a2/418 bytes (subjectPublicKeyInfo): 308201a2
 *        SEQ 13 bytes (algorithm): 300d
 *          OID 9 bytes: 0609 2a864886f70d010101 (OID_RSA_KEY_ALG 42.134.72.134.247.13.1.1.1)
 *          NULL: 0500
 *        BITSTRING 0x018f/399 bytes (publicKey): 0382018f
 *          ????: 00
 *          //after the zero byte, it appears key itself uses DER encoding:
 *          SEQ 0x018a/394 bytes: 3082018a
 *            INTEGER 0x0181/385 bytes (modulus): 02820181
 *                  00b1ab2fc727a3bef76780c9349bf3
 *                  ...24 more blocks of 15 bytes each...
 *                  90e895291c6bc8693b65
 *            INTEGER 3 bytes (exponent): 0203 010001
 *      [ASN_CONTEXT_SPECIFIC | ASN_CONSTRUCTED | 0x3] 0x01e5 bytes (X509v3 extensions): a38201e5
 *        SEQ 0x01e1 bytes: 308201e1
 *        ...
 * Certificate is a sequence of three elements:
 *      tbsCertificate (SEQ)
 *      signatureAlgorithm (AlgorithmIdentifier)
 *      signatureValue (BIT STRING)
 *
 * In turn, tbsCertificate is a sequence of:
 *      version
 *      serialNumber
 *      signatureAlgo (AlgorithmIdentifier)
 *      issuer (Name, has complex structure)
 *      validity (Validity, SEQ of two Times)
 *      subject (Name)
 *      subjectPublicKeyInfo (SEQ)
 *      ...
 *
 * subjectPublicKeyInfo is a sequence of:
 *      algorithm (AlgorithmIdentifier)
 *      publicKey (BIT STRING)
 *
 * We need Certificate.tbsCertificate.subjectPublicKeyInfo.publicKey
 *
 * Example of an ECDSA key:
 *      SEQ 0x59 bytes (subjectPublicKeyInfo): 3059
 *        SEQ 0x13 bytes (algorithm): 3013
 *          OID 7 bytes: 0607 2a8648ce3d0201   (OID_ECDSA_KEY_ALG 42.134.72.206.61.2.1)
 *          OID 8 bytes: 0608 2a8648ce3d030107 (OID_EC_prime256v1 42.134.72.206.61.3.1.7)
 *        BITSTRING 0x42 bytes (publicKey): 0342
 *          0004 53af f65e 50cc 7959 7e29 0171 c75c
 *          7335 e07d f45b 9750 b797 3a38 aebb 2ac6
 *          8329 2748 e77e 41cb d482 2ce6 05ec a058
 *          f3ab d561 2f4c d845 9ad3 7252 e3de bd3b
 *          9012
 */
        uint8_t *end = der + len;

        /* enter "Certificate" item: [der, end) will be only Cert */
        der = enter_der_item(der, &end);

        /* enter "tbsCertificate" item: [der, end) will be only tbsCert */
        der = enter_der_item(der, &end);

        /*
         * Skip version field only if it is present. For a v1 certificate, the
         * version field won't be present since v1 is the default value for the
         * version field and fields with default values should be omitted (see
         * RFC 5280 sections 4.1 and 4.1.2.1). If the version field is present
         * it will have a tag class of 2 (context-specific), bit 6 as 1
         * (constructed), and a tag number of 0 (see ITU-T X.690 sections 8.1.2
         * and 8.14).
         */
        /* bits 7-6: 10 */
        /* bit 5: 1 */
        /* bits 4-0: 00000 */
        if (der[0] == 0xa0)
                der = skip_der_item(der, end); /* version */

        /* skip up to subjectPublicKeyInfo */
        der = skip_der_item(der, end); /* serialNumber */
        der = skip_der_item(der, end); /* signatureAlgo */
        der = skip_der_item(der, end); /* issuer */
        der = skip_der_item(der, end); /* validity */
        der = skip_der_item(der, end); /* subject */

        /* enter subjectPublicKeyInfo */
        der = enter_der_item(der, &end);
        { /* check subjectPublicKeyInfo.algorithm */
                static const uint8_t OID_RSA_KEY_ALG[] ALIGN1 = {
                        0x30,0x0d, // SEQ 13 bytes
                        0x06,0x09, 0x2a,0x86,0x48,0x86,0xf7,0x0d,0x01,0x01,0x01, //OID_RSA_KEY_ALG 42.134.72.134.247.13.1.1.1
                        //0x05,0x00, // NULL
                };
                static const uint8_t OID_ECDSA_KEY_ALG[] ALIGN1 = {
                        0x30,0x13, // SEQ 0x13 bytes
                        0x06,0x07, 0x2a,0x86,0x48,0xce,0x3d,0x02,0x01,      //OID_ECDSA_KEY_ALG 42.134.72.206.61.2.1
                //allow any curve code for now...
                //      0x06,0x08, 0x2a,0x86,0x48,0xce,0x3d,0x03,0x01,0x07, //OID_EC_prime256v1 42.134.72.206.61.3.1.7
                        //RFC 3279:
                        //42.134.72.206.61.3     is ellipticCurve
                        //42.134.72.206.61.3.0   is c-TwoCurve
                        //42.134.72.206.61.3.1   is primeCurve
                        //42.134.72.206.61.3.1.7 is curve_secp256r1
                };
                if (memcmp(der, OID_RSA_KEY_ALG, sizeof(OID_RSA_KEY_ALG)) == 0) {
                        dbg("RSA key\n");
                        tls->flags |= GOT_CERT_RSA_KEY_ALG;
                } else
                if (memcmp(der, OID_ECDSA_KEY_ALG, sizeof(OID_ECDSA_KEY_ALG)) == 0) {
                        dbg("ECDSA key\n");
                        //UNUSED: tls->flags |= GOT_CERT_ECDSA_KEY_ALG;
                } else
                        bb_error_msg_and_die("not RSA or ECDSA cert");
        }

        if (tls->flags & GOT_CERT_RSA_KEY_ALG) {
                /* parse RSA key: */
        //based on getAsnRsaPubKey(), pkcs1ParsePrivBin() is also of note
                /* skip subjectPublicKeyInfo.algorithm */
                der = skip_der_item(der, end);
                /* enter subjectPublicKeyInfo.publicKey */
                //die_if_not_this_der_type(der, end, 0x03); /* must be BITSTRING */
                der = enter_der_item(der, &end);

                dbg("key bytes:%u, first:0x%02x\n", (int)(end - der), der[0]);
                if (end - der < 14)
                        xfunc_die();
                /* example format:
                 * ignore bits: 00
                 * SEQ 0x018a/394 bytes: 3082018a
                 *   INTEGER 0x0181/385 bytes (modulus): 02820181 XX...XXX
                 *   INTEGER 3 bytes (exponent): 0203 010001
                 */
                if (*der != 0) /* "ignore bits", should be 0 */
                        xfunc_die();
                der++;
                der = enter_der_item(der, &end); /* enter SEQ */
                /* memset(tls->hsd->server_rsa_pub_key, 0, sizeof(tls->hsd->server_rsa_pub_key)); - already is */
                der_binary_to_pstm(&tls->hsd->server_rsa_pub_key.N, der, end); /* modulus */
                der = skip_der_item(der, end);
                der_binary_to_pstm(&tls->hsd->server_rsa_pub_key.e, der, end); /* exponent */
                tls->hsd->server_rsa_pub_key.size = pstm_unsigned_bin_size(&tls->hsd->server_rsa_pub_key.N);
                dbg("server_rsa_pub_key.size:%d\n", tls->hsd->server_rsa_pub_key.size);
        }
        /* else: ECDSA key. It is not used for generating encryption keys,
         * it is used only to sign the EC public key (which comes in ServerKey message).
         * Since we do not verify cert validity, verifying signature on EC public key
         * wouldn't add any security. Thus, we do nothing here.
         */
}

/*
 * TLS Handshake routines
 */
static int tls_xread_handshake_block(tls_state_t *tls, int min_len)
{
        struct record_hdr *xhdr;
        int len = tls_xread_record(tls, "handshake record");

        xhdr = (void*)tls->inbuf;
        if (len < min_len
         || xhdr->type != RECORD_TYPE_HANDSHAKE
        ) {
                bad_record_die(tls, "handshake record", len);
        }
        dbg("got HANDSHAKE\n");
        return len;
}

static ALWAYS_INLINE void fill_handshake_record_hdr(void *buf, unsigned type, unsigned len)
{
        struct handshake_hdr {
                uint8_t type;
                uint8_t len24_hi, len24_mid, len24_lo;
        } *h = buf;

        len -= 4;
        h->type = type;
        h->len24_hi  = len >> 16;
        h->len24_mid = len >> 8;
        h->len24_lo  = len & 0xff;
}

static void send_client_hello_and_alloc_hsd(tls_state_t *tls, const char *sni)
{
#define NUM_CIPHERS (7 + 6 * ENABLE_FEATURE_TLS_SHA1 + ALLOW_RSA_NULL_SHA256)
        static const uint8_t ciphers[] = {
                0x00,2 + NUM_CIPHERS*2, //len16_be
                0x00,0xFF, //not a cipher - TLS_EMPTY_RENEGOTIATION_INFO_SCSV
                /* ^^^^^^ RFC 5746 Renegotiation Indication Extension - some servers will refuse to work with us otherwise */
#if ENABLE_FEATURE_TLS_SHA1
                0xC0,0x09, // 1 TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA - ok: wget https://is.gd/
                0xC0,0x0A, // 2 TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA - ok: wget https://is.gd/
                0xC0,0x13, // 3 TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA - ok: openssl s_server ... -cipher ECDHE-RSA-AES128-SHA
                0xC0,0x14, // 4 TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA - ok: openssl s_server ... -cipher ECDHE-RSA-AES256-SHA (might fail with older openssl)
        //      0xC0,0x18, //   TLS_ECDH_anon_WITH_AES_128_CBC_SHA
        //      0xC0,0x19, //   TLS_ECDH_anon_WITH_AES_256_CBC_SHA
#endif
                0xC0,0x23, // 5 TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256 - ok: wget https://is.gd/
        //      0xC0,0x24, //   TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384 - can't do SHA384 yet
                0xC0,0x27, // 6 TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 - ok: openssl s_server ... -cipher ECDHE-RSA-AES128-SHA256
        //      0xC0,0x28, //   TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384 - can't do SHA384 yet
                0xC0,0x2B, // 7 TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 - ok: wget https://is.gd/
        //      0xC0,0x2C, //   TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 - wget https://is.gd/: "TLS error from peer (alert code 20): bad MAC"
//TODO: GCM_SHA384 ciphers can be supported, only need sha384-based PRF?
                0xC0,0x2F, // 8 TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 - ok: openssl s_server ... -cipher ECDHE-RSA-AES128-GCM-SHA256
        //      0xC0,0x30, //   TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 - openssl s_server ... -cipher ECDHE-RSA-AES256-GCM-SHA384: "decryption failed or bad record mac"
        //possibly these too:
#if ENABLE_FEATURE_TLS_SHA1
        //      0xC0,0x35, //   TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA
        //      0xC0,0x36, //   TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA
#endif
        //      0xC0,0x37, //   TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA256
        //      0xC0,0x38, //   TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA384 - can't do SHA384 yet
#if ENABLE_FEATURE_TLS_SHA1
                0x00,0x2F, // 9 TLS_RSA_WITH_AES_128_CBC_SHA - ok: openssl s_server ... -cipher AES128-SHA
                0x00,0x35, //10 TLS_RSA_WITH_AES_256_CBC_SHA - ok: openssl s_server ... -cipher AES256-SHA
#endif
                0x00,0x3C, //11 TLS_RSA_WITH_AES_128_CBC_SHA256 - ok: openssl s_server ... -cipher AES128-SHA256
                0x00,0x3D, //12 TLS_RSA_WITH_AES_256_CBC_SHA256 - ok: openssl s_server ... -cipher AES256-SHA256
                0x00,0x9C, //13 TLS_RSA_WITH_AES_128_GCM_SHA256 - ok: openssl s_server ... -cipher AES128-GCM-SHA256
        //      0x00,0x9D, //   TLS_RSA_WITH_AES_256_GCM_SHA384 - openssl s_server ... -cipher AES256-GCM-SHA384: "decryption failed or bad record mac"
#if ALLOW_RSA_NULL_SHA256
                0x00,0x3B, //   TLS_RSA_WITH_NULL_SHA256
#endif
                0x01,0x00, //not a cipher - comprtypes_len, comprtype
        };
        static const uint8_t supported_groups[] = {
                0x00,0x0a, //extension_type: "supported_groups"
                0x00,0x04, //ext len
                0x00,0x02, //list len
                0x00,0x1d, //curve_x25519 (RFC 7748)
                //0x00,0x1e, //curve_x448 (RFC 7748)
                //0x00,0x17, //curve_secp256r1
                //0x00,0x18, //curve_secp384r1
                //0x00,0x19, //curve_secp521r1
//TODO: implement secp256r1 (at least): dl.fedoraproject.org immediately aborts
//if only x25519/x448 are advertised, seems to support only secpNNNr1 curves:
// openssl s_client -connect dl.fedoraproject.org:443 -debug -tls1_2 -cipher ECDHE-RSA-AES128-GCM-SHA256
//Peer signing digest: SHA512
//Peer signature type: RSA
//Server Temp Key: ECDH, P-256, 256 bits
//TLSv1.2, Cipher is ECDHE-RSA-AES128-GCM-SHA256
        };
        //static const uint8_t signature_algorithms[] = {
        //      000d
        //      0020
        //      001e
        //      0601 0602 0603 0501 0502 0503 0401 0402 0403 0301 0302 0303 0201 0202 0203
        //};

        struct client_hello {
                uint8_t type;
                uint8_t len24_hi, len24_mid, len24_lo;
                uint8_t proto_maj, proto_min;
                uint8_t rand32[32];
                uint8_t session_id_len;
                /* uint8_t session_id[]; */
                uint8_t cipherid_len16_hi, cipherid_len16_lo;
                uint8_t cipherid[2 + NUM_CIPHERS*2]; /* actually variable */
                uint8_t comprtypes_len;
                uint8_t comprtypes[1]; /* actually variable */
                /* Extensions (SNI shown):
                 * hi,lo // len of all extensions
                 *   00,00 // extension_type: "Server Name"
                 *   00,0e // list len (there can be more than one SNI)
                 *     00,0c // len of 1st Server Name Indication
                 *       00    // name type: host_name
                 *       00,09   // name len
                 *       "localhost" // name
                 */
// GNU Wget 1.18 to cdn.kernel.org sends these extensions:
// 0055
//   0005 0005 0100000000 - status_request
//   0000 0013 0011 00 000e 63646e 2e 6b65726e656c 2e 6f7267 - server_name
//   ff01 0001 00 - renegotiation_info
//   0023 0000 - session_ticket
//   000a 0008 0006001700180019 - supported_groups
//   000b 0002 0100 - ec_point_formats
//   000d 0016 0014 0401 0403 0501 0503 0601 0603 0301 0303 0201 0203 - signature_algorithms
// wolfssl library sends this option, RFC 7627 (closes a security weakness, some servers may require it. TODO?):
//   0017 0000 - extended master secret
        };
        struct client_hello *record;
        uint8_t *ptr;
        int len;
        int ext_len;
        int sni_len = sni ? strnlen(sni, 127 - 5) : 0;

        ext_len = 0;
        /* is.gd responds with "handshake failure" to our hello if there's no supported_groups element */
        ext_len += sizeof(supported_groups);
        if (sni_len)
                ext_len += 9 + sni_len;

        /* +2 is for "len of all extensions" 2-byte field */
        len = sizeof(*record) + 2 + ext_len;
        record = tls_get_zeroed_outbuf(tls, len);

        fill_handshake_record_hdr(record, HANDSHAKE_CLIENT_HELLO, len);
        record->proto_maj = TLS_MAJ;    /* the "requested" version of the protocol, */
        record->proto_min = TLS_MIN;    /* can be higher than one in record headers */
        tls_get_random(record->rand32, sizeof(record->rand32));
        if (TLS_DEBUG_FIXED_SECRETS)
                memset(record->rand32, 0x11, sizeof(record->rand32));
        /* record->session_id_len = 0; - already is */

        BUILD_BUG_ON(sizeof(ciphers) != 2 + 2 + NUM_CIPHERS*2 + 2);
        memcpy(&record->cipherid_len16_hi, ciphers, sizeof(ciphers));

        ptr = (void*)(record + 1);
        *ptr++ = ext_len >> 8;
        *ptr++ = ext_len;
        if (sni_len) {
                //ptr[0] = 0;             //
                //ptr[1] = 0;             //extension_type
                //ptr[2] = 0;         //
                ptr[3] = sni_len + 5; //list len
                //ptr[4] = 0;             //
                ptr[5] = sni_len + 3;     //len of 1st SNI
                //ptr[6] = 0;         //name type
                //ptr[7] = 0;             //
                ptr[8] = sni_len;         //name len
                ptr = mempcpy(&ptr[9], sni, sni_len);
        }
        memcpy(ptr, supported_groups, sizeof(supported_groups));

        tls->hsd = xzalloc(sizeof(*tls->hsd));
        /* HANDSHAKE HASH: ^^^ + len if need to save saved_client_hello */
        memcpy(tls->hsd->client_and_server_rand32, record->rand32, sizeof(record->rand32));
/* HANDSHAKE HASH:
        tls->hsd->saved_client_hello_size = len;
        memcpy(tls->hsd->saved_client_hello, record, len);
 */
        dbg(">> CLIENT_HELLO\n");
        /* Can hash immediately only if we know which MAC hash to use.
         * So far we do know: it's sha256:
         */
        sha256_begin(&tls->hsd->handshake_hash_ctx);
        xwrite_and_update_handshake_hash(tls, len);
        /* if this would become infeasible: save tls->hsd->saved_client_hello,
         * use "xwrite_handshake_record(tls, len)" here,
         * and hash saved_client_hello later.
         */
}

static void get_server_hello(tls_state_t *tls)
{
        struct server_hello {
                struct record_hdr xhdr;
                uint8_t type;
                uint8_t len24_hi, len24_mid, len24_lo;
                uint8_t proto_maj, proto_min;
                uint8_t rand32[32]; /* first 4 bytes are unix time in BE format */
                uint8_t session_id_len;
                uint8_t session_id[32];
                uint8_t cipherid_hi, cipherid_lo;
                uint8_t comprtype;
                /* extensions may follow, but only those which client offered in its Hello */
        };

        struct server_hello *hp;
        uint8_t *cipherid;
        uint8_t cipherid1;
        int len, len24;

        len = tls_xread_handshake_block(tls, 74 - 32);

        hp = (void*)tls->inbuf;
        // 74 bytes:
        // 02  000046 03|03   58|78|cf|c1 50|a5|49|ee|7e|29|48|71|fe|97|fa|e8|2d|19|87|72|90|84|9d|37|a3|f0|cb|6f|5f|e3|3c|2f |20  |d8|1a|78|96|52|d6|91|01|24|b3|d6|5b|b7|d0|6c|b3|e1|78|4e|3c|95|de|74|a0|ba|eb|a7|3a|ff|bd|a2|bf |00|9c |00|
        //SvHl len=70 maj.min unixtime^^^ 28randbytes^^^^^^^^^^^^^^^^^^^^^^^^^^^^_^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^_^^^ slen sid32bytes^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cipSel comprSel
        if (hp->type != HANDSHAKE_SERVER_HELLO
         || hp->len24_hi  != 0
         || hp->len24_mid != 0
         /* hp->len24_lo checked later */
         || hp->proto_maj != TLS_MAJ
         || hp->proto_min != TLS_MIN
        ) {
                bad_record_die(tls, "'server hello'", len);
        }

        cipherid = &hp->cipherid_hi;
        len24 = hp->len24_lo;
        if (hp->session_id_len != 32) {
                if (hp->session_id_len != 0)
                        bad_record_die(tls, "'server hello'", len);

                // session_id_len == 0: no session id
                // "The server
                // may return an empty session_id to indicate that the session will
                // not be cached and therefore cannot be resumed."
                cipherid -= 32;
                len24 += 32; /* what len would be if session id would be present */
        }

        if (len24 < 70)
                bad_record_die(tls, "'server hello'", len);
        dbg("<< SERVER_HELLO\n");

        memcpy(tls->hsd->client_and_server_rand32 + 32, hp->rand32, sizeof(hp->rand32));

        /* Set up encryption params based on selected cipher */
#if 0
#if ENABLE_FEATURE_TLS_SHA1
                0xC0,0x09, // 1 TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA - ok: wget https://is.gd/
                0xC0,0x0A, // 2 TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA - ok: wget https://is.gd/
                0xC0,0x13, // 3 TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA - ok: openssl s_server ... -cipher ECDHE-RSA-AES128-SHA
                0xC0,0x14, // 4 TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA - ok: openssl s_server ... -cipher ECDHE-RSA-AES256-SHA (might fail with older openssl)
        //      0xC0,0x18, //   TLS_ECDH_anon_WITH_AES_128_CBC_SHA
        //      0xC0,0x19, //   TLS_ECDH_anon_WITH_AES_256_CBC_SHA
#endif
                0xC0,0x23, // 5 TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256 - ok: wget https://is.gd/
        //      0xC0,0x24, //   TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384 - can't do SHA384 yet
                0xC0,0x27, // 6 TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 - ok: openssl s_server ... -cipher ECDHE-RSA-AES128-SHA256
        //      0xC0,0x28, //   TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384 - can't do SHA384 yet
                0xC0,0x2B, // 7 TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 - ok: wget https://is.gd/
        //      0xC0,0x2C, //   TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 - wget https://is.gd/: "TLS error from peer (alert code 20): bad MAC"
//TODO: GCM_SHA384 ciphers can be supported, only need sha384-based PRF?
                0xC0,0x2F, // 8 TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 - ok: openssl s_server ... -cipher ECDHE-RSA-AES128-GCM-SHA256
        //      0xC0,0x30, //   TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 - openssl s_server ... -cipher ECDHE-RSA-AES256-GCM-SHA384: "decryption failed or bad record mac"
        //possibly these too:
#if ENABLE_FEATURE_TLS_SHA1
        //      0xC0,0x35, //   TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA
        //      0xC0,0x36, //   TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA
#endif
        //      0xC0,0x37, //   TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA256
        //      0xC0,0x38, //   TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA384 - can't do SHA384 yet
#if ENABLE_FEATURE_TLS_SHA1
                0x00,0x2F, // 9 TLS_RSA_WITH_AES_128_CBC_SHA - ok: openssl s_server ... -cipher AES128-SHA
                0x00,0x35, //10 TLS_RSA_WITH_AES_256_CBC_SHA - ok: openssl s_server ... -cipher AES256-SHA
#endif
                0x00,0x3C, //11 TLS_RSA_WITH_AES_128_CBC_SHA256 - ok: openssl s_server ... -cipher AES128-SHA256
                0x00,0x3D, //12 TLS_RSA_WITH_AES_256_CBC_SHA256 - ok: openssl s_server ... -cipher AES256-SHA256
                0x00,0x9C, //13 TLS_RSA_WITH_AES_128_GCM_SHA256 - ok: openssl s_server ... -cipher AES128-GCM-SHA256
        //      0x00,0x9D, //   TLS_RSA_WITH_AES_256_GCM_SHA384 - openssl s_server ... -cipher AES256-GCM-SHA384: "decryption failed or bad record mac"
#if ALLOW_RSA_NULL_SHA256
                0x00,0x3B, //   TLS_RSA_WITH_NULL_SHA256
#endif
#endif
        cipherid1 = cipherid[1];
        tls->cipher_id = 0x100 * cipherid[0] + cipherid1;
        tls->key_size = AES256_KEYSIZE;
        tls->MAC_size = SHA256_OUTSIZE;
        /*tls->IV_size = 0; - already is */
        if (cipherid[0] == 0xC0) {
                /* All C0xx are ECDHE */
                tls->flags |= NEED_EC_KEY;
                if (cipherid1 & 1) {
                        /* Odd numbered C0xx use AES128 (even ones use AES256) */
                        tls->key_size = AES128_KEYSIZE;
                }
                if (ENABLE_FEATURE_TLS_SHA1 && cipherid1 <= 0x19) {
                        tls->MAC_size = SHA1_OUTSIZE;
                } else
                if (cipherid1 >= 0x2B && cipherid1 <= 0x30) {
                        /* C02B,2C,2F,30 are AES-GCM */
                        tls->flags |= ENCRYPTION_AESGCM;
                        tls->MAC_size = 0;
                        tls->IV_size = 4;
                }
        } else {
                /* All 00xx are RSA */
                if ((ENABLE_FEATURE_TLS_SHA1 && cipherid1 == 0x2F)
                 || cipherid1 == 0x3C
                 || cipherid1 == 0x9C
                ) {
                        tls->key_size = AES128_KEYSIZE;
                }
                if (ENABLE_FEATURE_TLS_SHA1 && cipherid1 <= 0x35) {
                        tls->MAC_size = SHA1_OUTSIZE;
                } else
                if (cipherid1 == 0x9C /*|| cipherid1 == 0x9D*/) {
                        /* 009C,9D are AES-GCM */
                        tls->flags |= ENCRYPTION_AESGCM;
                        tls->MAC_size = 0;
                        tls->IV_size = 4;
                }
        }
        dbg("server chose cipher %04x\n", tls->cipher_id);
        dbg("key_size:%u MAC_size:%u IV_size:%u\n", tls->key_size, tls->MAC_size, tls->IV_size);

        /* Handshake hash eventually destined to FINISHED record
         * is sha256 regardless of cipher
         * (at least for all ciphers defined by RFC5246).
         * It's not sha1 for AES_128_CBC_SHA - only MAC is sha1, not this hash.
         */
/* HANDSHAKE HASH:
        sha256_begin(&tls->hsd->handshake_hash_ctx);
        hash_handshake(tls, ">> client hello hash:%s",
                tls->hsd->saved_client_hello, tls->hsd->saved_client_hello_size
        );
        hash_handshake(tls, "<< server hello hash:%s",
                tls->inbuf + RECHDR_LEN, len
        );
 */
}

static void get_server_cert(tls_state_t *tls)
{
        struct record_hdr *xhdr;
        uint8_t *certbuf;
        int len, len1;

        len = tls_xread_handshake_block(tls, 10);

        xhdr = (void*)tls->inbuf;
        certbuf = (void*)(xhdr + 1);
        if (certbuf[0] != HANDSHAKE_CERTIFICATE)
                bad_record_die(tls, "certificate", len);
        dbg("<< CERTIFICATE\n");
        // 4392 bytes:
        // 0b  00|11|24 00|11|21 00|05|b0 30|82|05|ac|30|82|04|94|a0|03|02|01|02|02|11|00|9f|85|bf|66|4b|0c|dd|af|ca|50|86|79|50|1b|2b|e4|30|0d...
        //Cert len=4388 ChainLen CertLen^ DER encoded X509 starts here. openssl x509 -in FILE -inform DER -noout -text
        len1 = get24be(certbuf + 1);
        if (len1 > len - 4) tls_error_die(tls);
        len = len1;
        len1 = get24be(certbuf + 4);
        if (len1 > len - 3) tls_error_die(tls);
        len = len1;
        len1 = get24be(certbuf + 7);
        if (len1 > len - 3) tls_error_die(tls);
        len = len1;

        if (len)
                find_key_in_der_cert(tls, certbuf + 10, len);
}

/* On input, len is known to be >= 4.
 * The record is known to be SERVER_KEY_EXCHANGE.
 */
static void process_server_key(tls_state_t *tls, int len)
{
        struct record_hdr *xhdr;
        uint8_t *keybuf;
        int len1;
        uint32_t t32;

        xhdr = (void*)tls->inbuf;
        keybuf = (void*)(xhdr + 1);
//seen from is.gd: it selects curve_x25519:
//  0c 00006e //SERVER_KEY_EXCHANGE, len
//    03 //curve_type: named curve
//    001d //curve_x25519
//server-chosen EC point, and then signed_params
//      (RFC 8422: "A hash of the params, with the signature
//      appropriate to that hash applied.  The private key corresponding
//      to the certified public key in the server's Certificate message is
//      used for signing.")
//follow. Format unclear/guessed:
//    20 //eccPubKeyLen
//      25511923d73b70dd2f60e66ba2f3fda31a9c25170963c7a3a972e481dbb2835d //eccPubKey (32bytes)
//    0203 //hashSigAlg: 2:SHA1 (4:SHA256 5:SHA384 6:SHA512), 3:ECDSA (1:RSA)
//    0046 //len (16bit)
//      30 44 //SEQ, len
//        02 20 //INTEGER, len
//          2e18e7c2a9badd0a70cd3059a6ab114539b9f5163568911147386cd77ed7c412 //32bytes
//this item ^^^^^ is sometimes 33 bytes (with all container sizes also +1)
//        02 20 //INTEGER, len
//          64523d6216cb94c43c9b20e377d8c52c55be6703fd6730a155930c705eaf3af6 //32bytes
//same about this item ^^^^^

//seen from ftp.openbsd.org
//(which only accepts ECDHE-RSA-AESnnn-GCM-SHAnnn and ECDHE-RSA-CHACHA20-POLY1305 ciphers):
//  0c 000228 //SERVER_KEY_EXCHANGE, len
//    03 //curve_type: named curve
//    001d //curve_x25519
//    20 //eccPubKeyLen
//      eef7a15c43b71a4c7eaa48a39369399cc4332e569ec90a83274cc92596705c1a //eccPubKey
//    0401 //hashSigAlg: 4:SHA256, 1:RSA
//    0200 //len
//      //0x200 bytes follow

        /* Get and verify length */
        len1 = get24be(keybuf + 1);
        if (len1 > len - 4) tls_error_die(tls);
        len = len1;
        if (len < (1+2+1+32)) tls_error_die(tls);
        keybuf += 4;

        /* So far we only support curve_x25519 */
        move_from_unaligned32(t32, keybuf);
        if (t32 != htonl(0x03001d20))
                bb_error_msg_and_die("elliptic curve is not x25519");

        memcpy(tls->hsd->ecc_pub_key32, keybuf + 4, 32);
        tls->flags |= GOT_EC_KEY;
        dbg("got eccPubKey\n");
}

static void send_empty_client_cert(tls_state_t *tls)
{
        struct client_empty_cert {
                uint8_t type;
                uint8_t len24_hi, len24_mid, len24_lo;
                uint8_t cert_chain_len24_hi, cert_chain_len24_mid, cert_chain_len24_lo;
        };
        struct client_empty_cert *record;

        record = tls_get_zeroed_outbuf(tls, sizeof(*record));
        //fill_handshake_record_hdr(record, HANDSHAKE_CERTIFICATE, sizeof(*record));
        //record->cert_chain_len24_hi = 0;
        //record->cert_chain_len24_mid = 0;
        //record->cert_chain_len24_lo = 0;
        // same as above:
        record->type = HANDSHAKE_CERTIFICATE;
        record->len24_lo = 3;

        dbg(">> CERTIFICATE\n");
        xwrite_and_update_handshake_hash(tls, sizeof(*record));
}

static void send_client_key_exchange(tls_state_t *tls)
{
        struct client_key_exchange {
                uint8_t type;
                uint8_t len24_hi, len24_mid, len24_lo;
                uint8_t key[2 + 4 * 1024]; // size??
        };
//FIXME: better size estimate
        struct client_key_exchange *record = tls_get_zeroed_outbuf(tls, sizeof(*record));
        uint8_t rsa_premaster[RSA_PREMASTER_SIZE];
        uint8_t x25519_premaster[CURVE25519_KEYSIZE];
        uint8_t *premaster;
        int premaster_size;
        int len;

        if (!(tls->flags & NEED_EC_KEY)) {
                /* RSA */
                if (!(tls->flags & GOT_CERT_RSA_KEY_ALG))
                        bb_error_msg("server cert is not RSA");

                tls_get_random(rsa_premaster, sizeof(rsa_premaster));
                if (TLS_DEBUG_FIXED_SECRETS)
                        memset(rsa_premaster, 0x44, sizeof(rsa_premaster));
                // RFC 5246
                // "Note: The version number in the PreMasterSecret is the version
                // offered by the client in the ClientHello.client_version, not the
                // version negotiated for the connection."
                rsa_premaster[0] = TLS_MAJ;
                rsa_premaster[1] = TLS_MIN;
                dump_hex("premaster:%s\n", rsa_premaster, sizeof(rsa_premaster));
                len = psRsaEncryptPub(/*pool:*/ NULL,
                        /* psRsaKey_t* */ &tls->hsd->server_rsa_pub_key,
                        rsa_premaster, /*inlen:*/ sizeof(rsa_premaster),
                        record->key + 2, sizeof(record->key) - 2,
                        data_param_ignored
                );
                /* keylen16 exists for RSA (in TLS, not in SSL), but not for some other key types */
                record->key[0] = len >> 8;
                record->key[1] = len & 0xff;
                len += 2;
                premaster = rsa_premaster;
                premaster_size = sizeof(rsa_premaster);
        } else {
                /* ECDHE */
                static const uint8_t basepoint9[CURVE25519_KEYSIZE] = {9};
                uint8_t privkey[CURVE25519_KEYSIZE]; //[32]

                if (!(tls->flags & GOT_EC_KEY))
                        bb_error_msg("server did not provide EC key");

                /* Generate random private key, see RFC 7748 */
                tls_get_random(privkey, sizeof(privkey));
                privkey[0] &= 0xf8;
                privkey[CURVE25519_KEYSIZE-1] = ((privkey[CURVE25519_KEYSIZE-1] & 0x7f) | 0x40);

                /* Compute public key */
                curve25519(record->key + 1, privkey, basepoint9);

                /* Compute premaster using peer's public key */
                dbg("computing x25519_premaster\n");
                curve25519(x25519_premaster, privkey, tls->hsd->ecc_pub_key32);

                len = CURVE25519_KEYSIZE;
                record->key[0] = len;
                len++;
                premaster = x25519_premaster;
                premaster_size = sizeof(x25519_premaster);
        }

        record->type = HANDSHAKE_CLIENT_KEY_EXCHANGE;
        /* record->len24_hi = 0; - already is */
        record->len24_mid = len >> 8;
        record->len24_lo  = len & 0xff;
        len += 4;

        dbg(">> CLIENT_KEY_EXCHANGE\n");
        xwrite_and_update_handshake_hash(tls, len);

        // RFC 5246
        // For all key exchange methods, the same algorithm is used to convert
        // the pre_master_secret into the master_secret.  The pre_master_secret
        // should be deleted from memory once the master_secret has been
        // computed.
        //      master_secret = PRF(pre_master_secret, "master secret",
        //                          ClientHello.random + ServerHello.random)
        //                          [0..47];
        // The master secret is always exactly 48 bytes in length.  The length

        // of the premaster secret will vary depending on key exchange method.
        prf_hmac_sha256(/*tls,*/
                tls->hsd->master_secret, sizeof(tls->hsd->master_secret),
                premaster, premaster_size,
                "master secret",
                tls->hsd->client_and_server_rand32, sizeof(tls->hsd->client_and_server_rand32)
        );
        dump_hex("master secret:%s\n", tls->hsd->master_secret, sizeof(tls->hsd->master_secret));

        // RFC 5246
        // 6.3.  Key Calculation
        //
        // The Record Protocol requires an algorithm to generate keys required
        // by the current connection state (see Appendix A.6) from the security
        // parameters provided by the handshake protocol.
        //
        // The master secret is expanded into a sequence of secure bytes, which
        // is then split to a client write MAC key, a server write MAC key, a
        // client write encryption key, and a server write encryption key.  Each
        // of these is generated from the byte sequence in that order.  Unused
        // values are empty.  Some AEAD ciphers may additionally require a
        // client write IV and a server write IV (see Section 6.2.3.3).
        //
        // When keys and MAC keys are generated, the master secret is used as an
        // entropy source.
        //
        // To generate the key material, compute
        //
        //    key_block = PRF(SecurityParameters.master_secret,
        //                    "key expansion",
        //                    SecurityParameters.server_random +
        //                    SecurityParameters.client_random);
        //
        // until enough output has been generated.  Then, the key_block is
        // partitioned as follows:
        //
        //    client_write_MAC_key[SecurityParameters.mac_key_length]
        //    server_write_MAC_key[SecurityParameters.mac_key_length]
        //    client_write_key[SecurityParameters.enc_key_length]
        //    server_write_key[SecurityParameters.enc_key_length]
        //    client_write_IV[SecurityParameters.fixed_iv_length]
        //    server_write_IV[SecurityParameters.fixed_iv_length]
        {
                uint8_t tmp64[64];

                /* make "server_rand32 + client_rand32" */
                memcpy(&tmp64[0] , &tls->hsd->client_and_server_rand32[32], 32);
                memcpy(&tmp64[32], &tls->hsd->client_and_server_rand32[0] , 32);

                prf_hmac_sha256(/*tls,*/
                        tls->client_write_MAC_key, 2 * (tls->MAC_size + tls->key_size + tls->IV_size),
                        // also fills:
                        // server_write_MAC_key[]
                        // client_write_key[]
                        // server_write_key[]
                        // client_write_IV[]
                        // server_write_IV[]
                        tls->hsd->master_secret, sizeof(tls->hsd->master_secret),
                        "key expansion",
                        tmp64, 64
                );
                tls->client_write_key = tls->client_write_MAC_key + (2 * tls->MAC_size);
                tls->server_write_key = tls->client_write_key + tls->key_size;
                tls->client_write_IV = tls->server_write_key + tls->key_size;
                tls->server_write_IV = tls->client_write_IV + tls->IV_size;
                dump_hex("client_write_MAC_key:%s\n",
                        tls->client_write_MAC_key, tls->MAC_size
                );
                dump_hex("client_write_key:%s\n",
                        tls->client_write_key, tls->key_size
                );
                dump_hex("client_write_IV:%s\n",
                        tls->client_write_IV, tls->IV_size
                );

                aes_setkey(&tls->aes_decrypt, tls->server_write_key, tls->key_size);
                aes_setkey(&tls->aes_encrypt, tls->client_write_key, tls->key_size);
                {
                        uint8_t iv[AES_BLOCK_SIZE];
                        memset(iv, 0, AES_BLOCK_SIZE);
                        aes_encrypt_one_block(&tls->aes_encrypt, iv, tls->H);
                }
        }
}

static const uint8_t rec_CHANGE_CIPHER_SPEC[] ALIGN1 = {
        RECORD_TYPE_CHANGE_CIPHER_SPEC, TLS_MAJ, TLS_MIN, 00, 01,
        01
};

static void send_change_cipher_spec(tls_state_t *tls)
{
        dbg(">> CHANGE_CIPHER_SPEC\n");
        xwrite(tls->ofd, rec_CHANGE_CIPHER_SPEC, sizeof(rec_CHANGE_CIPHER_SPEC));
}

// 7.4.9.  Finished
// A Finished message is always sent immediately after a change
// cipher spec message to verify that the key exchange and
// authentication processes were successful.  It is essential that a
// change cipher spec message be received between the other handshake
// messages and the Finished message.
//...
// The Finished message is the first one protected with the just
// negotiated algorithms, keys, and secrets.  Recipients of Finished
// messages MUST verify that the contents are correct.  Once a side
// has sent its Finished message and received and validated the
// Finished message from its peer, it may begin to send and receive
// application data over the connection.
//...
// struct {
//     opaque verify_data[verify_data_length];
// } Finished;
//
// verify_data
//    PRF(master_secret, finished_label, Hash(handshake_messages))
//       [0..verify_data_length-1];
//
// finished_label
//    For Finished messages sent by the client, the string
//    "client finished".  For Finished messages sent by the server,
//    the string "server finished".
//
// Hash denotes a Hash of the handshake messages.  For the PRF
// defined in Section 5, the Hash MUST be the Hash used as the basis
// for the PRF.  Any cipher suite which defines a different PRF MUST
// also define the Hash to use in the Finished computation.
//
// In previous versions of TLS, the verify_data was always 12 octets
// long.  In the current version of TLS, it depends on the cipher
// suite.  Any cipher suite which does not explicitly specify
// verify_data_length has a verify_data_length equal to 12.  This
// includes all existing cipher suites.
static void send_client_finished(tls_state_t *tls)
{
        struct finished {
                uint8_t type;
                uint8_t len24_hi, len24_mid, len24_lo;
                uint8_t prf_result[12];
        };
        struct finished *record = tls_get_outbuf(tls, sizeof(*record));
        uint8_t handshake_hash[TLS_MAX_MAC_SIZE];
        unsigned len;

        fill_handshake_record_hdr(record, HANDSHAKE_FINISHED, sizeof(*record));

        len = sha_end(&tls->hsd->handshake_hash_ctx, handshake_hash);

        prf_hmac_sha256(/*tls,*/
                record->prf_result, sizeof(record->prf_result),
                tls->hsd->master_secret, sizeof(tls->hsd->master_secret),
                "client finished",
                handshake_hash, len
        );
        dump_hex("from secret: %s\n", tls->hsd->master_secret, sizeof(tls->hsd->master_secret));
        dump_hex("from labelSeed: %s", "client finished", sizeof("client finished")-1);
        dump_hex("%s\n", handshake_hash, sizeof(handshake_hash));
        dump_hex("=> digest: %s\n", record->prf_result, sizeof(record->prf_result));

        dbg(">> FINISHED\n");
        xwrite_encrypted(tls, sizeof(*record), RECORD_TYPE_HANDSHAKE);
}

void FAST_FUNC tls_handshake(tls_state_t *tls, const char *sni)
{
        // Client              RFC 5246                Server
        // (*) - optional messages, not always sent
        //
        // ClientHello          ------->
        //                                        ServerHello
        //                                       Certificate*
        //                                 ServerKeyExchange*
        //                                CertificateRequest*
        //                      <-------      ServerHelloDone
        // Certificate*
        // ClientKeyExchange
        // CertificateVerify*
        // [ChangeCipherSpec]
        // Finished             ------->
        //                                 [ChangeCipherSpec]
        //                      <-------             Finished
        // Application Data     <------>     Application Data
        int len;
        int got_cert_req;

        send_client_hello_and_alloc_hsd(tls, sni);
        get_server_hello(tls);

        // RFC 5246
        // The server MUST send a Certificate message whenever the agreed-
        // upon key exchange method uses certificates for authentication
        // (this includes all key exchange methods defined in this document
        // except DH_anon).  This message will always immediately follow the
        // ServerHello message.
        //
        // IOW: in practice, Certificate *always* follows.
        // (for example, kernel.org does not even accept DH_anon cipher id)
        get_server_cert(tls);

        len = tls_xread_handshake_block(tls, 4);
        if (tls->inbuf[RECHDR_LEN] == HANDSHAKE_SERVER_KEY_EXCHANGE) {
                // 459 bytes:
                // 0c   00|01|c7 03|00|17|41|04|87|94|2e|2f|68|d0|c9|f4|97|a8|2d|ef|ed|67|ea|c6|f3|b3|56|47|5d|27|b6|bd|ee|70|25|30|5e|b0|8e|f6|21|5a...
                //SvKey len=455^
                // with TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA: 461 bytes:
                // 0c   00|01|c9 03|00|17|41|04|cd|9b|b4|29|1f|f6|b0|c2|84|82|7f|29|6a|47|4e|ec|87|0b|c1|9c|69|e1|f8|c6|d0|53|e9|27|90|a5|c8|02|15|75...
                //
                // RFC 8422 5.4. Server Key Exchange
                // This message is sent when using the ECDHE_ECDSA, ECDHE_RSA, and
                // ECDH_anon key exchange algorithms.
                // This message is used to convey the server's ephemeral ECDH public key
                // (and the corresponding elliptic curve domain parameters) to the
                // client.
                dbg("<< SERVER_KEY_EXCHANGE len:%u\n", len);
                dump_raw_in("<< %s\n", tls->inbuf, RECHDR_LEN + len);
                if (tls->flags & NEED_EC_KEY)
                        process_server_key(tls, len);

                // read next handshake block
                len = tls_xread_handshake_block(tls, 4);
        }

        got_cert_req = (tls->inbuf[RECHDR_LEN] == HANDSHAKE_CERTIFICATE_REQUEST);
        if (got_cert_req) {
                dbg("<< CERTIFICATE_REQUEST\n");
                // RFC 5246: "If no suitable certificate is available,
                // the client MUST send a certificate message containing no
                // certificates.  That is, the certificate_list structure has a
                // length of zero. ...
                // Client certificates are sent using the Certificate structure
                // defined in Section 7.4.2."
                // (i.e. the same format as server certs)

                /*send_empty_client_cert(tls); - WRONG (breaks handshake hash calc) */
                /* need to hash _all_ server replies first, up to ServerHelloDone */
                len = tls_xread_handshake_block(tls, 4);
        }

        if (tls->inbuf[RECHDR_LEN] != HANDSHAKE_SERVER_HELLO_DONE) {
                bad_record_die(tls, "'server hello done'", len);
        }
        // 0e 000000 (len:0)
        dbg("<< SERVER_HELLO_DONE\n");

        if (got_cert_req)
                send_empty_client_cert(tls);

        send_client_key_exchange(tls);

        send_change_cipher_spec(tls);
        /* from now on we should send encrypted */
        /* tls->write_seq64_be = 0; - already is */
        tls->flags |= ENCRYPT_ON_WRITE;

        send_client_finished(tls);

        /* Get CHANGE_CIPHER_SPEC */
        len = tls_xread_record(tls, "switch to encrypted traffic");
        if (len != 1 || memcmp(tls->inbuf, rec_CHANGE_CIPHER_SPEC, 6) != 0)
                bad_record_die(tls, "switch to encrypted traffic", len);
        dbg("<< CHANGE_CIPHER_SPEC\n");

        if (ALLOW_RSA_NULL_SHA256
         && tls->cipher_id == TLS_RSA_WITH_NULL_SHA256
        ) {
                tls->min_encrypted_len_on_read = tls->MAC_size;
        } else
        if (!(tls->flags & ENCRYPTION_AESGCM)) {
                unsigned mac_blocks = (unsigned)(TLS_MAC_SIZE(tls) + AES_BLOCK_SIZE-1) / AES_BLOCK_SIZE;
                /* all incoming packets now should be encrypted and have
                 * at least IV + (MAC padded to blocksize):
                 */
                tls->min_encrypted_len_on_read = AES_BLOCK_SIZE + (mac_blocks * AES_BLOCK_SIZE);
        } else {
                tls->min_encrypted_len_on_read = 8 + AES_BLOCK_SIZE;
        }
        dbg("min_encrypted_len_on_read: %u\n", tls->min_encrypted_len_on_read);

        /* Get (encrypted) FINISHED from the server */
        len = tls_xread_record(tls, "'server finished'");
        if (len < 4 || tls->inbuf[RECHDR_LEN] != HANDSHAKE_FINISHED)
                bad_record_die(tls, "'server finished'", len);
        dbg("<< FINISHED\n");
        /* application data can be sent/received */

        /* free handshake data */
        psRsaKey_clear(&tls->hsd->server_rsa_pub_key);
//      if (PARANOIA)
//              memset(tls->hsd, 0, tls->hsd->hsd_size);
        free(tls->hsd);
        tls->hsd = NULL;
}

static void tls_xwrite(tls_state_t *tls, int len)
{
        dbg(">> DATA\n");
        xwrite_encrypted(tls, len, RECORD_TYPE_APPLICATION_DATA);
}

// To run a test server using openssl:
// openssl req -x509 -newkey rsa:$((4096/4*3)) -keyout key.pem -out server.pem -nodes -days 99999 -subj '/CN=localhost'
// openssl s_server -key key.pem -cert server.pem -debug -tls1_2
//
// Unencryped SHA256 example:
// openssl req -x509 -newkey rsa:$((4096/4*3)) -keyout key.pem -out server.pem -nodes -days 99999 -subj '/CN=localhost'
// openssl s_server -key key.pem -cert server.pem -debug -tls1_2 -cipher NULL
// openssl s_client -connect 127.0.0.1:4433 -debug -tls1_2 -cipher NULL-SHA256

void FAST_FUNC tls_run_copy_loop(tls_state_t *tls, unsigned flags)
{
        int inbuf_size;
        const int INBUF_STEP = 4 * 1024;
        struct pollfd pfds[2];

        pfds[0].fd = STDIN_FILENO;
        pfds[0].events = POLLIN;
        pfds[1].fd = tls->ifd;
        pfds[1].events = POLLIN;

        inbuf_size = INBUF_STEP;
        for (;;) {
                int nread;

                if (safe_poll(pfds, 2, -1) < 0)
                        bb_perror_msg_and_die("poll");

                if (pfds[0].revents) {
                        void *buf;

                        dbg("STDIN HAS DATA\n");
                        buf = tls_get_outbuf(tls, inbuf_size);
                        nread = safe_read(STDIN_FILENO, buf, inbuf_size);
                        if (nread < 1) {
                                /* We'd want to do this: */
                                /* Close outgoing half-connection so they get EOF,
                                 * but leave incoming alone so we can see response
                                 */
                                //shutdown(tls->ofd, SHUT_WR);
                                /* But TLS has no way to encode this,
                                 * doubt it's ok to do it "raw"
                                 */
                                pfds[0].fd = -1;
                                tls_free_outbuf(tls); /* mem usage optimization */
                                if (flags & TLSLOOP_EXIT_ON_LOCAL_EOF)
                                        break;
                        } else {
                                if (nread == inbuf_size) {
                                        /* TLS has per record overhead, if input comes fast,
                                         * read, encrypt and send bigger chunks
                                         */
                                        inbuf_size += INBUF_STEP;
                                        if (inbuf_size > TLS_MAX_OUTBUF)
                                                inbuf_size = TLS_MAX_OUTBUF;
                                }
                                tls_xwrite(tls, nread);
                        }
                }
                if (pfds[1].revents) {
                        dbg("NETWORK HAS DATA\n");
 read_record:
                        nread = tls_xread_record(tls, "encrypted data");
                        if (nread < 1) {
                                /* TLS protocol has no real concept of one-sided shutdowns:
                                 * if we get "TLS EOF" from the peer, writes will fail too
                                 */
                                //pfds[1].fd = -1;
                                //close(STDOUT_FILENO);
                                //tls_free_inbuf(tls); /* mem usage optimization */
                                //continue;
                                break;
                        }
                        if (tls->inbuf[0] != RECORD_TYPE_APPLICATION_DATA)
                                bad_record_die(tls, "encrypted data", nread);
                        xwrite(STDOUT_FILENO, tls->inbuf + RECHDR_LEN, nread);
                        /* We may already have a complete next record buffered,
                         * can process it without network reads (and possible blocking)
                         */
                        if (tls_has_buffered_record(tls))
                                goto read_record;
                }
        }
}