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annotate src/pk/dsa/dsa_verify_hash.c @ 191:1c15b283127b libtomcrypt-orig

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Import of libtomcrypt 1.02 with manual path rename rearrangement etc
author Matt Johnston <matt@ucc.asn.au>
date Fri, 06 May 2005 13:23:02 +0000
parents
children 39d5d58461d6
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191
1c15b283127b Import of libtomcrypt 1.02 with manual path rename rearrangement etc
Matt Johnston <matt@ucc.asn.au>
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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 "tomcrypt.h"
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12
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13 /**
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14 @file dsa_verify_hash.c
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15 DSA implementation, verify a signature, Tom St Denis
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16 */
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17
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18
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19 #ifdef MDSA
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20
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21 /**
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22 Verify a DSA signature
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23 @param sig The signature
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24 @param siglen The length of the signature (octets)
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25 @param hash The hash that was signed
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26 @param hashlen The length of the hash that was signed
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27 @param stat [out] The result of the signature verification, 1==valid, 0==invalid
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28 @param key The corresponding public DH key
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29 @return CRYPT_OK if successful (even if the signature is invalid)
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30 */
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31 int dsa_verify_hash(const unsigned char *sig, unsigned long siglen,
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32 const unsigned char *hash, unsigned long hashlen,
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33 int *stat, dsa_key *key)
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34 {
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35 mp_int r, s, w, v, u1, u2;
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36 int err;
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37
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38 LTC_ARGCHK(sig != NULL);
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39 LTC_ARGCHK(hash != NULL);
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40 LTC_ARGCHK(stat != NULL);
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41 LTC_ARGCHK(key != NULL);
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42
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43 /* default to invalid signature */
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44 *stat = 0;
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45
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46 /* init our variables */
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47 if ((err = mp_init_multi(&r, &s, &w, &v, &u1, &u2, NULL)) != MP_OKAY) {
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48 return mpi_to_ltc_error(err);
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49 }
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50
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51 /* read in r followed by s */
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52 if ((err = der_get_multi_integer(sig, &siglen, &r, &s, NULL)) != CRYPT_OK) { goto done; }
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53
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54 /* neither r or s can be null */
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55 if (mp_iszero(&r) == MP_YES || mp_iszero(&s) == MP_YES) {
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56 err = CRYPT_INVALID_PACKET;
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57 goto done;
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58 }
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59
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60 /* w = 1/s mod q */
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61 if ((err = mp_invmod(&s, &key->q, &w)) != MP_OKAY) { goto error; }
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62
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63 /* u1 = m * w mod q */
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64 if ((err = mp_read_unsigned_bin(&u1, (unsigned char *)hash, hashlen)) != MP_OKAY) { goto error; }
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65 if ((err = mp_mulmod(&u1, &w, &key->q, &u1)) != MP_OKAY) { goto error; }
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66
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67 /* u2 = r*w mod q */
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68 if ((err = mp_mulmod(&r, &w, &key->q, &u2)) != MP_OKAY) { goto error; }
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69
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70 /* v = g^u1 * y^u2 mod p mod q */
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71 if ((err = mp_exptmod(&key->g, &u1, &key->p, &u1)) != MP_OKAY) { goto error; }
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72 if ((err = mp_exptmod(&key->y, &u2, &key->p, &u2)) != MP_OKAY) { goto error; }
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73 if ((err = mp_mulmod(&u1, &u2, &key->p, &v)) != MP_OKAY) { goto error; }
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74 if ((err = mp_mod(&v, &key->q, &v)) != MP_OKAY) { goto error; }
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75
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76 /* if r = v then we're set */
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77 if (mp_cmp(&r, &v) == MP_EQ) {
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78 *stat = 1;
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79 }
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80
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81 err = CRYPT_OK;
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82 goto done;
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83
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84 error : err = mpi_to_ltc_error(err);
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85 done : mp_clear_multi(&r, &s, &w, &v, &u1, &u2, NULL);
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86 return err;
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87 }
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88
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89 #endif
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90