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1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis |
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2 * |
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3 * LibTomCrypt is a library that provides various cryptographic |
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4 * algorithms in a highly modular and flexible manner. |
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5 * |
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6 * The library is free for all purposes without any express |
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7 * guarantee it works. |
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8 * |
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9 * Tom St Denis, [email protected], http://libtomcrypt.org |
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10 */ |
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11 #include "mycrypt.h" |
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12 |
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13 #ifdef MDSA |
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14 |
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15 int dsa_verify_hash(const unsigned char *sig, unsigned long siglen, |
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16 const unsigned char *hash, unsigned long inlen, |
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17 int *stat, dsa_key *key) |
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18 { |
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19 mp_int r, s, w, v, u1, u2; |
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20 unsigned long x, y; |
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21 int err; |
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22 |
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23 _ARGCHK(sig != NULL); |
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24 _ARGCHK(hash != NULL); |
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25 _ARGCHK(stat != NULL); |
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26 _ARGCHK(key != NULL); |
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27 |
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28 /* default to invalid signature */ |
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29 *stat = 0; |
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30 |
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31 if (siglen < PACKET_SIZE+2+2) { |
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32 return CRYPT_INVALID_PACKET; |
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33 } |
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34 |
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35 /* is the message format correct? */ |
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36 if ((err = packet_valid_header((unsigned char *)sig, PACKET_SECT_DSA, PACKET_SUB_SIGNED)) != CRYPT_OK) { |
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37 return err; |
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38 } |
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39 |
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40 /* skip over header */ |
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41 y = PACKET_SIZE; |
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42 |
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43 /* init our variables */ |
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44 if ((err = mp_init_multi(&r, &s, &w, &v, &u1, &u2, NULL)) != MP_OKAY) { |
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45 return mpi_to_ltc_error(err); |
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46 } |
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47 |
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48 /* read in r followed by s */ |
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49 x = ((unsigned)sig[y]<<8)|((unsigned)sig[y+1]); |
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50 y += 2; |
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51 if (y + x > siglen) { |
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52 err = CRYPT_INVALID_PACKET; |
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53 goto done; |
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54 } |
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55 if ((err = mp_read_unsigned_bin(&r, (unsigned char *)sig+y, x)) != MP_OKAY) { goto error; } |
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56 y += x; |
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57 |
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58 /* load s */ |
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59 x = ((unsigned)sig[y]<<8)|((unsigned)sig[y+1]); |
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60 y += 2; |
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61 if (y + x > siglen) { |
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62 err = CRYPT_INVALID_PACKET; |
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63 goto done; |
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64 } |
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65 if ((err = mp_read_unsigned_bin(&s, (unsigned char *)sig+y, x)) != MP_OKAY) { goto error; } |
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66 |
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67 /* w = 1/s mod q */ |
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68 if ((err = mp_invmod(&s, &key->q, &w)) != MP_OKAY) { goto error; } |
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69 |
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70 /* u1 = m * w mod q */ |
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71 if ((err = mp_read_unsigned_bin(&u1, (unsigned char *)hash, inlen)) != MP_OKAY) { goto error; } |
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72 if ((err = mp_mulmod(&u1, &w, &key->q, &u1)) != MP_OKAY) { goto error; } |
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73 |
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74 /* u2 = r*w mod q */ |
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75 if ((err = mp_mulmod(&r, &w, &key->q, &u2)) != MP_OKAY) { goto error; } |
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76 |
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77 /* v = g^u1 * y^u2 mod p mod q */ |
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78 if ((err = mp_exptmod(&key->g, &u1, &key->p, &u1)) != MP_OKAY) { goto error; } |
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79 if ((err = mp_exptmod(&key->y, &u2, &key->p, &u2)) != MP_OKAY) { goto error; } |
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80 if ((err = mp_mulmod(&u1, &u2, &key->p, &v)) != MP_OKAY) { goto error; } |
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81 if ((err = mp_mod(&v, &key->q, &v)) != MP_OKAY) { goto error; } |
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82 |
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83 /* if r = v then we're set */ |
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84 if (mp_cmp(&r, &v) == MP_EQ) { |
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85 *stat = 1; |
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86 } |
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87 |
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88 err = CRYPT_OK; |
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89 goto done; |
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90 |
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91 error : err = mpi_to_ltc_error(err); |
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92 done : mp_clear_multi(&r, &s, &w, &v, &u1, &u2, NULL); |
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93 return err; |
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94 } |
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95 |
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96 #endif |
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97 |
