LXR linux/crypto/ecrdsa.c

   1// SPDX-License-Identifier: GPL-2.0+
   2/*
   3 * Elliptic Curve (Russian) Digital Signature Algorithm for Cryptographic API
   4 *
   5 * Copyright (c) 2019 Vitaly Chikunov <vt@altlinux.org>
   6 *
   7 * References:
   8 * GOST 34.10-2018, GOST R 34.10-2012, RFC 7091, ISO/IEC 14888-3:2018.
   9 *
  10 * Historical references:
  11 * GOST R 34.10-2001, RFC 4357, ISO/IEC 14888-3:2006/Amd 1:2010.
  12 *
  13 * This program is free software; you can redistribute it and/or modify it
  14 * under the terms of the GNU General Public License as published by the Free
  15 * Software Foundation; either version 2 of the License, or (at your option)
  16 * any later version.
  17 */
  18
  19#include <linux/module.h>
  20#include <linux/crypto.h>
  21#include <crypto/streebog.h>
  22#include <crypto/internal/akcipher.h>
  23#include <crypto/akcipher.h>
  24#include <linux/oid_registry.h>
  25#include "ecrdsa_params.asn1.h"
  26#include "ecrdsa_pub_key.asn1.h"
  27#include "ecc.h"
  28#include "ecrdsa_defs.h"
  29
  30#define ECRDSA_MAX_SIG_SIZE (2 * 512 / 8)
  31#define ECRDSA_MAX_DIGITS (512 / 64)
  32
  33struct ecrdsa_ctx {
  34        enum OID algo_oid; /* overall public key oid */
  35        enum OID curve_oid; /* parameter */
  36        enum OID digest_oid; /* parameter */
  37        const struct ecc_curve *curve; /* curve from oid */
  38        unsigned int digest_len; /* parameter (bytes) */
  39        const char *digest; /* digest name from oid */
  40        unsigned int key_len; /* @key length (bytes) */
  41        const char *key; /* raw public key */
  42        struct ecc_point pub_key;
  43        u64 _pubp[2][ECRDSA_MAX_DIGITS]; /* point storage for @pub_key */
  44};
  45
  46static const struct ecc_curve *get_curve_by_oid(enum OID oid)
  47{
  48        switch (oid) {
  49        case OID_gostCPSignA:
  50        case OID_gostTC26Sign256B:
  51                return &gost_cp256a;
  52        case OID_gostCPSignB:
  53        case OID_gostTC26Sign256C:
  54                return &gost_cp256b;
  55        case OID_gostCPSignC:
  56        case OID_gostTC26Sign256D:
  57                return &gost_cp256c;
  58        case OID_gostTC26Sign512A:
  59                return &gost_tc512a;
  60        case OID_gostTC26Sign512B:
  61                return &gost_tc512b;
  62        /* The following two aren't implemented: */
  63        case OID_gostTC26Sign256A:
  64        case OID_gostTC26Sign512C:
  65        default:
  66                return NULL;
  67        }
  68}
  69
  70static int ecrdsa_verify(struct akcipher_request *req)
  71{
  72        struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
  73        struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm);
  74        unsigned char sig[ECRDSA_MAX_SIG_SIZE];
  75        unsigned char digest[STREEBOG512_DIGEST_SIZE];
  76        unsigned int ndigits = req->dst_len / sizeof(u64);
  77        u64 r[ECRDSA_MAX_DIGITS]; /* witness (r) */
  78        u64 _r[ECRDSA_MAX_DIGITS]; /* -r */
  79        u64 s[ECRDSA_MAX_DIGITS]; /* second part of sig (s) */
  80        u64 e[ECRDSA_MAX_DIGITS]; /* h \mod q */
  81        u64 *v = e;               /* e^{-1} \mod q */
  82        u64 z1[ECRDSA_MAX_DIGITS];
  83        u64 *z2 = _r;
  84        struct ecc_point cc = ECC_POINT_INIT(s, e, ndigits); /* reuse s, e */
  85
  86        /*
  87         * Digest value, digest algorithm, and curve (modulus) should have the
  88         * same length (256 or 512 bits), public key and signature should be
  89         * twice bigger.
  90         */
  91        if (!ctx->curve ||
  92            !ctx->digest ||
  93            !req->src ||
  94            !ctx->pub_key.x ||
  95            req->dst_len != ctx->digest_len ||
  96            req->dst_len != ctx->curve->g.ndigits * sizeof(u64) ||
  97            ctx->pub_key.ndigits != ctx->curve->g.ndigits ||
  98            req->dst_len * 2 != req->src_len ||
  99            WARN_ON(req->src_len > sizeof(sig)) ||
 100            WARN_ON(req->dst_len > sizeof(digest)))
 101                return -EBADMSG;
 102
 103        sg_copy_to_buffer(req->src, sg_nents_for_len(req->src, req->src_len),
 104                          sig, req->src_len);
 105        sg_pcopy_to_buffer(req->src,
 106                           sg_nents_for_len(req->src,
 107                                            req->src_len + req->dst_len),
 108                           digest, req->dst_len, req->src_len);
 109
 110        vli_from_be64(s, sig, ndigits);
 111        vli_from_be64(r, sig + ndigits * sizeof(u64), ndigits);
 112
 113        /* Step 1: verify that 0 < r < q, 0 < s < q */
 114        if (vli_is_zero(r, ndigits) ||
 115            vli_cmp(r, ctx->curve->n, ndigits) == 1 ||
 116            vli_is_zero(s, ndigits) ||
 117            vli_cmp(s, ctx->curve->n, ndigits) == 1)
 118                return -EKEYREJECTED;
 119
 120        /* Step 2: calculate hash (h) of the message (passed as input) */
 121        /* Step 3: calculate e = h \mod q */
 122        vli_from_le64(e, digest, ndigits);
 123        if (vli_cmp(e, ctx->curve->n, ndigits) == 1)
 124                vli_sub(e, e, ctx->curve->n, ndigits);
 125        if (vli_is_zero(e, ndigits))
 126                e[0] = 1;
 127
 128        /* Step 4: calculate v = e^{-1} \mod q */
 129        vli_mod_inv(v, e, ctx->curve->n, ndigits);
 130
 131        /* Step 5: calculate z_1 = sv \mod q, z_2 = -rv \mod q */
 132        vli_mod_mult_slow(z1, s, v, ctx->curve->n, ndigits);
 133        vli_sub(_r, ctx->curve->n, r, ndigits);
 134        vli_mod_mult_slow(z2, _r, v, ctx->curve->n, ndigits);
 135
 136        /* Step 6: calculate point C = z_1P + z_2Q, and R = x_c \mod q */
 137        ecc_point_mult_shamir(&cc, z1, &ctx->curve->g, z2, &ctx->pub_key,
 138                              ctx->curve);
 139        if (vli_cmp(cc.x, ctx->curve->n, ndigits) == 1)
 140                vli_sub(cc.x, cc.x, ctx->curve->n, ndigits);
 141
 142        /* Step 7: if R == r signature is valid */
 143        if (!vli_cmp(cc.x, r, ndigits))
 144                return 0;
 145        else
 146                return -EKEYREJECTED;
 147}
 148
 149int ecrdsa_param_curve(void *context, size_t hdrlen, unsigned char tag,
 150                       const void *value, size_t vlen)
 151{
 152        struct ecrdsa_ctx *ctx = context;
 153
 154        ctx->curve_oid = look_up_OID(value, vlen);
 155        if (!ctx->curve_oid)
 156                return -EINVAL;
 157        ctx->curve = get_curve_by_oid(ctx->curve_oid);
 158        return 0;
 159}
 160
 161/* Optional. If present should match expected digest algo OID. */
 162int ecrdsa_param_digest(void *context, size_t hdrlen, unsigned char tag,
 163                        const void *value, size_t vlen)
 164{
 165        struct ecrdsa_ctx *ctx = context;
 166        int digest_oid = look_up_OID(value, vlen);
 167
 168        if (digest_oid != ctx->digest_oid)
 169                return -EINVAL;
 170        return 0;
 171}
 172
 173int ecrdsa_parse_pub_key(void *context, size_t hdrlen, unsigned char tag,
 174                         const void *value, size_t vlen)
 175{
 176        struct ecrdsa_ctx *ctx = context;
 177
 178        ctx->key = value;
 179        ctx->key_len = vlen;
 180        return 0;
 181}
 182
 183static u8 *ecrdsa_unpack_u32(u32 *dst, void *src)
 184{
 185        memcpy(dst, src, sizeof(u32));
 186        return src + sizeof(u32);
 187}
 188
 189/* Parse BER encoded subjectPublicKey. */
 190static int ecrdsa_set_pub_key(struct crypto_akcipher *tfm, const void *key,
 191                              unsigned int keylen)
 192{
 193        struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm);
 194        unsigned int ndigits;
 195        u32 algo, paramlen;
 196        u8 *params;
 197        int err;
 198
 199        err = asn1_ber_decoder(&ecrdsa_pub_key_decoder, ctx, key, keylen);
 200        if (err < 0)
 201                return err;
 202
 203        /* Key parameters is in the key after keylen. */
 204        params = ecrdsa_unpack_u32(&paramlen,
 205                          ecrdsa_unpack_u32(&algo, (u8 *)key + keylen));
 206
 207        if (algo == OID_gost2012PKey256) {
 208                ctx->digest     = "streebog256";
 209                ctx->digest_oid = OID_gost2012Digest256;
 210                ctx->digest_len = 256 / 8;
 211        } else if (algo == OID_gost2012PKey512) {
 212                ctx->digest     = "streebog512";
 213                ctx->digest_oid = OID_gost2012Digest512;
 214                ctx->digest_len = 512 / 8;
 215        } else
 216                return -ENOPKG;
 217        ctx->algo_oid = algo;
 218
 219        /* Parse SubjectPublicKeyInfo.AlgorithmIdentifier.parameters. */
 220        err = asn1_ber_decoder(&ecrdsa_params_decoder, ctx, params, paramlen);
 221        if (err < 0)
 222                return err;
 223        /*
 224         * Sizes of algo (set in digest_len) and curve should match
 225         * each other.
 226         */
 227        if (!ctx->curve ||
 228            ctx->curve->g.ndigits * sizeof(u64) != ctx->digest_len)
 229                return -ENOPKG;
 230        /*
 231         * Key is two 256- or 512-bit coordinates which should match
 232         * curve size.
 233         */
 234        if ((ctx->key_len != (2 * 256 / 8) &&
 235             ctx->key_len != (2 * 512 / 8)) ||
 236            ctx->key_len != ctx->curve->g.ndigits * sizeof(u64) * 2)
 237                return -ENOPKG;
 238
 239        ndigits = ctx->key_len / sizeof(u64) / 2;
 240        ctx->pub_key = ECC_POINT_INIT(ctx->_pubp[0], ctx->_pubp[1], ndigits);
 241        vli_from_le64(ctx->pub_key.x, ctx->key, ndigits);
 242        vli_from_le64(ctx->pub_key.y, ctx->key + ndigits * sizeof(u64),
 243                      ndigits);
 244
 245        if (ecc_is_pubkey_valid_partial(ctx->curve, &ctx->pub_key))
 246                return -EKEYREJECTED;
 247
 248        return 0;
 249}
 250
 251static unsigned int ecrdsa_max_size(struct crypto_akcipher *tfm)
 252{
 253        struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm);
 254
 255        /*
 256         * Verify doesn't need any output, so it's just informational
 257         * for keyctl to determine the key bit size.
 258         */
 259        return ctx->pub_key.ndigits * sizeof(u64);
 260}
 261
 262static void ecrdsa_exit_tfm(struct crypto_akcipher *tfm)
 263{
 264}
 265
 266static struct akcipher_alg ecrdsa_alg = {
 267        .verify         = ecrdsa_verify,
 268        .set_pub_key    = ecrdsa_set_pub_key,
 269        .max_size       = ecrdsa_max_size,
 270        .exit           = ecrdsa_exit_tfm,
 271        .base = {
 272                .cra_name        = "ecrdsa",
 273                .cra_driver_name = "ecrdsa-generic",
 274                .cra_priority    = 100,
 275                .cra_module      = THIS_MODULE,
 276                .cra_ctxsize     = sizeof(struct ecrdsa_ctx),
 277        },
 278};
 279
 280static int __init ecrdsa_mod_init(void)
 281{
 282        return crypto_register_akcipher(&ecrdsa_alg);
 283}
 284
 285static void __exit ecrdsa_mod_fini(void)
 286{
 287        crypto_unregister_akcipher(&ecrdsa_alg);
 288}
 289
 290module_init(ecrdsa_mod_init);
 291module_exit(ecrdsa_mod_fini);
 292
 293MODULE_LICENSE("GPL");
 294MODULE_AUTHOR("Vitaly Chikunov <vt@altlinux.org>");
 295MODULE_DESCRIPTION("EC-RDSA generic algorithm");
 296MODULE_ALIAS_CRYPTO("ecrdsa-generic");
 297