1/* LibTomCrypt, modular cryptographic library -- Tom St Denis
2 *
3 * LibTomCrypt is a library that provides various cryptographic
4 * algorithms in a highly modular and flexible manner.
5 *
6 * The library is free for all purposes without any express
7 * guarantee it works.
8 *
9 * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com
10 */
11#include "tomcrypt.h"
12
13/**
14   @file dsa_verify_hash.c
15   DSA implementation, verify a signature, Tom St Denis
16*/
17
18
19#ifdef MDSA
20
21/**
22  Verify a DSA signature
23  @param r        DSA "r" parameter
24  @param s        DSA "s" parameter
25  @param hash     The hash that was signed
26  @param hashlen  The length of the hash that was signed
27  @param stat     [out] The result of the signature verification, 1==valid, 0==invalid
28  @param key      The corresponding public DH key
29  @return CRYPT_OK if successful (even if the signature is invalid)
30*/
31int dsa_verify_hash_raw(         void   *r,          void   *s,
32                    const unsigned char *hash, unsigned long hashlen,
33                                    int *stat,      dsa_key *key)
34{
35   void          *w, *v, *u1, *u2;
36   int           err;
37
38   LTC_ARGCHK(r    != NULL);
39   LTC_ARGCHK(s    != NULL);
40   LTC_ARGCHK(stat != NULL);
41   LTC_ARGCHK(key  != NULL);
42
43   /* default to invalid signature */
44   *stat = 0;
45
46   /* init our variables */
47   if ((err = mp_init_multi(&w, &v, &u1, &u2, NULL)) != CRYPT_OK) {
48      return err;
49   }
50
51   /* neither r or s can be null or >q*/
52   if (mp_iszero(r) == LTC_MP_YES || mp_iszero(s) == LTC_MP_YES || mp_cmp(r, key->q) != LTC_MP_LT || mp_cmp(s, key->q) != LTC_MP_LT) {
53      err = CRYPT_INVALID_PACKET;
54      goto error;
55   }
56
57   /* w = 1/s mod q */
58   if ((err = mp_invmod(s, key->q, w)) != CRYPT_OK)                                       { goto error; }
59
60   /* u1 = m * w mod q */
61   if ((err = mp_read_unsigned_bin(u1, (unsigned char *)hash, hashlen)) != CRYPT_OK)      { goto error; }
62   if ((err = mp_mulmod(u1, w, key->q, u1)) != CRYPT_OK)                                  { goto error; }
63
64   /* u2 = r*w mod q */
65   if ((err = mp_mulmod(r, w, key->q, u2)) != CRYPT_OK)                                   { goto error; }
66
67   /* v = g^u1 * y^u2 mod p mod q */
68   if ((err = mp_exptmod(key->g, u1, key->p, u1)) != CRYPT_OK)                            { goto error; }
69   if ((err = mp_exptmod(key->y, u2, key->p, u2)) != CRYPT_OK)                            { goto error; }
70   if ((err = mp_mulmod(u1, u2, key->p, v)) != CRYPT_OK)                                  { goto error; }
71   if ((err = mp_mod(v, key->q, v)) != CRYPT_OK)                                          { goto error; }
72
73   /* if r = v then we're set */
74   if (mp_cmp(r, v) == LTC_MP_EQ) {
75      *stat = 1;
76   }
77
78   err = CRYPT_OK;
79error:
80   mp_clear_multi(w, v, u1, u2, NULL);
81   return err;
82}
83
84/**
85  Verify a DSA signature
86  @param sig      The signature
87  @param siglen   The length of the signature (octets)
88  @param hash     The hash that was signed
89  @param hashlen  The length of the hash that was signed
90  @param stat     [out] The result of the signature verification, 1==valid, 0==invalid
91  @param key      The corresponding public DH key
92  @return CRYPT_OK if successful (even if the signature is invalid)
93*/
94int dsa_verify_hash(const unsigned char *sig, unsigned long siglen,
95                    const unsigned char *hash, unsigned long hashlen,
96                    int *stat, dsa_key *key)
97{
98   int    err;
99   void   *r, *s;
100
101   if ((err = mp_init_multi(&r, &s, NULL)) != CRYPT_OK) {
102      return CRYPT_MEM;
103   }
104
105   /* decode the sequence */
106   if ((err = der_decode_sequence_multi(sig, siglen,
107                                  LTC_ASN1_INTEGER, 1UL, r,
108                                  LTC_ASN1_INTEGER, 1UL, s,
109                                  LTC_ASN1_EOL,     0UL, NULL)) != CRYPT_OK) {
110      goto LBL_ERR;
111   }
112
113   /* do the op */
114   err = dsa_verify_hash_raw(r, s, hash, hashlen, stat, key);
115
116LBL_ERR:
117   mp_clear_multi(r, s, NULL);
118   return err;
119}
120
121#endif
122
123
124/* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_verify_hash.c,v $ */
125/* $Revision: 1.13 $ */
126/* $Date: 2006/12/04 03:18:43 $ */
127