Mercurial > dropbear

annotate dsa_verify_hash.c @ 17:1a066933c5e1 libtomcrypt

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Removed PDFs, if people want them there's the .tex
author Matt Johnston <matt@ucc.asn.au>
date Tue, 15 Jun 2004 14:32:29 +0000
parents d7da3b1e1540
children
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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