LXR linux/crypto/asymmetric

   1/* RSA asymmetric public-key algorithm [RFC3447]
   2 *
   3 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
   4 * Written by David Howells (dhowells@redhat.com)
   5 *
   6 * This program is free software; you can redistribute it and/or
   7 * modify it under the terms of the GNU General Public Licence
   8 * as published by the Free Software Foundation; either version
   9 * 2 of the Licence, or (at your option) any later version.
  10 */
  11
  12#define pr_fmt(fmt) "RSA: "fmt
  13#include <linux/module.h>
  14#include <linux/kernel.h>
  15#include <linux/slab.h>
  16#include <crypto/algapi.h>
  17#include "public_key.h"
  18
  19MODULE_LICENSE("GPL");
  20MODULE_DESCRIPTION("RSA Public Key Algorithm");
  21
  22#define kenter(FMT, ...) \
  23        pr_devel("==> %s("FMT")\n", __func__, ##__VA_ARGS__)
  24#define kleave(FMT, ...) \
  25        pr_devel("<== %s()"FMT"\n", __func__, ##__VA_ARGS__)
  26
  27/*
  28 * Hash algorithm OIDs plus ASN.1 DER wrappings [RFC4880 sec 5.2.2].
  29 */
  30static const u8 RSA_digest_info_MD5[] = {
  31        0x30, 0x20, 0x30, 0x0C, 0x06, 0x08,
  32        0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* OID */
  33        0x05, 0x00, 0x04, 0x10
  34};
  35
  36static const u8 RSA_digest_info_SHA1[] = {
  37        0x30, 0x21, 0x30, 0x09, 0x06, 0x05,
  38        0x2B, 0x0E, 0x03, 0x02, 0x1A,
  39        0x05, 0x00, 0x04, 0x14
  40};
  41
  42static const u8 RSA_digest_info_RIPE_MD_160[] = {
  43        0x30, 0x21, 0x30, 0x09, 0x06, 0x05,
  44        0x2B, 0x24, 0x03, 0x02, 0x01,
  45        0x05, 0x00, 0x04, 0x14
  46};
  47
  48static const u8 RSA_digest_info_SHA224[] = {
  49        0x30, 0x2d, 0x30, 0x0d, 0x06, 0x09,
  50        0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x04,
  51        0x05, 0x00, 0x04, 0x1C
  52};
  53
  54static const u8 RSA_digest_info_SHA256[] = {
  55        0x30, 0x31, 0x30, 0x0d, 0x06, 0x09,
  56        0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01,
  57        0x05, 0x00, 0x04, 0x20
  58};
  59
  60static const u8 RSA_digest_info_SHA384[] = {
  61        0x30, 0x41, 0x30, 0x0d, 0x06, 0x09,
  62        0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02,
  63        0x05, 0x00, 0x04, 0x30
  64};
  65
  66static const u8 RSA_digest_info_SHA512[] = {
  67        0x30, 0x51, 0x30, 0x0d, 0x06, 0x09,
  68        0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03,
  69        0x05, 0x00, 0x04, 0x40
  70};
  71
  72static const struct {
  73        const u8 *data;
  74        size_t size;
  75} RSA_ASN1_templates[PKEY_HASH__LAST] = {
  76#define _(X) { RSA_digest_info_##X, sizeof(RSA_digest_info_##X) }
  77        [HASH_ALGO_MD5]         = _(MD5),
  78        [HASH_ALGO_SHA1]        = _(SHA1),
  79        [HASH_ALGO_RIPE_MD_160] = _(RIPE_MD_160),
  80        [HASH_ALGO_SHA256]      = _(SHA256),
  81        [HASH_ALGO_SHA384]      = _(SHA384),
  82        [HASH_ALGO_SHA512]      = _(SHA512),
  83        [HASH_ALGO_SHA224]      = _(SHA224),
  84#undef _
  85};
  86
  87/*
  88 * RSAVP1() function [RFC3447 sec 5.2.2]
  89 */
  90static int RSAVP1(const struct public_key *key, MPI s, MPI *_m)
  91{
  92        MPI m;
  93        int ret;
  94
  95        /* (1) Validate 0 <= s < n */
  96        if (mpi_cmp_ui(s, 0) < 0) {
  97                kleave(" = -EBADMSG [s < 0]");
  98                return -EBADMSG;
  99        }
 100        if (mpi_cmp(s, key->rsa.n) >= 0) {
 101                kleave(" = -EBADMSG [s >= n]");
 102                return -EBADMSG;
 103        }
 104
 105        m = mpi_alloc(0);
 106        if (!m)
 107                return -ENOMEM;
 108
 109        /* (2) m = s^e mod n */
 110        ret = mpi_powm(m, s, key->rsa.e, key->rsa.n);
 111        if (ret < 0) {
 112                mpi_free(m);
 113                return ret;
 114        }
 115
 116        *_m = m;
 117        return 0;
 118}
 119
 120/*
 121 * Integer to Octet String conversion [RFC3447 sec 4.1]
 122 */
 123static int RSA_I2OSP(MPI x, size_t xLen, u8 **_X)
 124{
 125        unsigned X_size, x_size;
 126        int X_sign;
 127        u8 *X;
 128
 129        /* Make sure the string is the right length.  The number should begin
 130         * with { 0x00, 0x01, ... } so we have to account for 15 leading zero
 131         * bits not being reported by MPI.
 132         */
 133        x_size = mpi_get_nbits(x);
 134        pr_devel("size(x)=%u xLen*8=%zu\n", x_size, xLen * 8);
 135        if (x_size != xLen * 8 - 15)
 136                return -ERANGE;
 137
 138        X = mpi_get_buffer(x, &X_size, &X_sign);
 139        if (!X)
 140                return -ENOMEM;
 141        if (X_sign < 0) {
 142                kfree(X);
 143                return -EBADMSG;
 144        }
 145        if (X_size != xLen - 1) {
 146                kfree(X);
 147                return -EBADMSG;
 148        }
 149
 150        *_X = X;
 151        return 0;
 152}
 153
 154/*
 155 * Perform the RSA signature verification.
 156 * @H: Value of hash of data and metadata
 157 * @EM: The computed signature value
 158 * @k: The size of EM (EM[0] is an invalid location but should hold 0x00)
 159 * @hash_size: The size of H
 160 * @asn1_template: The DigestInfo ASN.1 template
 161 * @asn1_size: Size of asm1_template[]
 162 */
 163static int RSA_verify(const u8 *H, const u8 *EM, size_t k, size_t hash_size,
 164                      const u8 *asn1_template, size_t asn1_size)
 165{
 166        unsigned PS_end, T_offset, i;
 167
 168        kenter(",,%zu,%zu,%zu", k, hash_size, asn1_size);
 169
 170        if (k < 2 + 1 + asn1_size + hash_size)
 171                return -EBADMSG;
 172
 173        /* Decode the EMSA-PKCS1-v1_5 */
 174        if (EM[1] != 0x01) {
 175                kleave(" = -EBADMSG [EM[1] == %02u]", EM[1]);
 176                return -EBADMSG;
 177        }
 178
 179        T_offset = k - (asn1_size + hash_size);
 180        PS_end = T_offset - 1;
 181        if (EM[PS_end] != 0x00) {
 182                kleave(" = -EBADMSG [EM[T-1] == %02u]", EM[PS_end]);
 183                return -EBADMSG;
 184        }
 185
 186        for (i = 2; i < PS_end; i++) {
 187                if (EM[i] != 0xff) {
 188                        kleave(" = -EBADMSG [EM[PS%x] == %02u]", i - 2, EM[i]);
 189                        return -EBADMSG;
 190                }
 191        }
 192
 193        if (crypto_memneq(asn1_template, EM + T_offset, asn1_size) != 0) {
 194                kleave(" = -EBADMSG [EM[T] ASN.1 mismatch]");
 195                return -EBADMSG;
 196        }
 197
 198        if (crypto_memneq(H, EM + T_offset + asn1_size, hash_size) != 0) {
 199                kleave(" = -EKEYREJECTED [EM[T] hash mismatch]");
 200                return -EKEYREJECTED;
 201        }
 202
 203        kleave(" = 0");
 204        return 0;
 205}
 206
 207/*
 208 * Perform the verification step [RFC3447 sec 8.2.2].
 209 */
 210static int RSA_verify_signature(const struct public_key *key,
 211                                const struct public_key_signature *sig)
 212{
 213        size_t tsize;
 214        int ret;
 215
 216        /* Variables as per RFC3447 sec 8.2.2 */
 217        const u8 *H = sig->digest;
 218        u8 *EM = NULL;
 219        MPI m = NULL;
 220        size_t k;
 221
 222        kenter("");
 223
 224        if (!RSA_ASN1_templates[sig->pkey_hash_algo].data)
 225                return -ENOTSUPP;
 226
 227        /* (1) Check the signature size against the public key modulus size */
 228        k = mpi_get_nbits(key->rsa.n);
 229        tsize = mpi_get_nbits(sig->rsa.s);
 230
 231        /* According to RFC 4880 sec 3.2, length of MPI is computed starting
 232         * from most significant bit.  So the RFC 3447 sec 8.2.2 size check
 233         * must be relaxed to conform with shorter signatures - so we fail here
 234         * only if signature length is longer than modulus size.
 235         */
 236        pr_devel("step 1: k=%zu size(S)=%zu\n", k, tsize);
 237        if (k < tsize) {
 238                ret = -EBADMSG;
 239                goto error;
 240        }
 241
 242        /* Round up and convert to octets */
 243        k = (k + 7) / 8;
 244
 245        /* (2b) Apply the RSAVP1 verification primitive to the public key */
 246        ret = RSAVP1(key, sig->rsa.s, &m);
 247        if (ret < 0)
 248                goto error;
 249
 250        /* (2c) Convert the message representative (m) to an encoded message
 251         *      (EM) of length k octets.
 252         *
 253         *      NOTE!  The leading zero byte is suppressed by MPI, so we pass a
 254         *      pointer to the _preceding_ byte to RSA_verify()!
 255         */
 256        ret = RSA_I2OSP(m, k, &EM);
 257        if (ret < 0)
 258                goto error;
 259
 260        ret = RSA_verify(H, EM - 1, k, sig->digest_size,
 261                         RSA_ASN1_templates[sig->pkey_hash_algo].data,
 262                         RSA_ASN1_templates[sig->pkey_hash_algo].size);
 263
 264error:
 265        kfree(EM);
 266        mpi_free(m);
 267        kleave(" = %d", ret);
 268        return ret;
 269}
 270
 271const struct public_key_algorithm RSA_public_key_algorithm = {
 272        .name           = "RSA",
 273        .n_pub_mpi      = 2,
 274        .n_sec_mpi      = 3,
 275        .n_sig_mpi      = 1,
 276        .verify_signature = RSA_verify_signature,
 277};
 278EXPORT_SYMBOL_GPL(RSA_public_key_algorithm);
 279