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_sign_hash.c
15   DSA implementation, sign a hash, Tom St Denis
16*/
17
18#ifdef MDSA
19
20/**
21  Sign a hash with DSA
22  @param in       The hash to sign
23  @param inlen    The length of the hash to sign
24  @param r        The "r" integer of the signature (caller must initialize with mp_init() first)
25  @param s        The "s" integer of the signature (caller must initialize with mp_init() first)
26  @param prng     An active PRNG state
27  @param wprng    The index of the PRNG desired
28  @param key      A private DSA key
29  @return CRYPT_OK if successful
30*/
31int dsa_sign_hash_raw(const unsigned char *in,  unsigned long inlen,
32                                   void   *r,   void *s,
33                               prng_state *prng, int wprng, dsa_key *key)
34{
35   void         *k, *kinv, *tmp;
36   unsigned char *buf;
37   int            err;
38
39   LTC_ARGCHK(in  != NULL);
40   LTC_ARGCHK(r   != NULL);
41   LTC_ARGCHK(s   != NULL);
42   LTC_ARGCHK(key != NULL);
43
44   if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
45      return err;
46   }
47   if (key->type != PK_PRIVATE) {
48      return CRYPT_PK_NOT_PRIVATE;
49   }
50
51   /* check group order size  */
52   if (key->qord >= MDSA_MAX_GROUP) {
53      return CRYPT_INVALID_ARG;
54   }
55
56   buf = XMALLOC(MDSA_MAX_GROUP);
57   if (buf == NULL) {
58      return CRYPT_MEM;
59   }
60
61   /* Init our temps */
62   if ((err = mp_init_multi(&k, &kinv, &tmp, NULL)) != CRYPT_OK)                       { goto ERRBUF; }
63
64retry:
65
66   do {
67      /* gen random k */
68      if (prng_descriptor[wprng].read(buf, key->qord, prng) != (unsigned long)key->qord) {
69         err = CRYPT_ERROR_READPRNG;
70         goto error;
71      }
72
73      /* read k */
74      if ((err = mp_read_unsigned_bin(k, buf, key->qord)) != CRYPT_OK)                 { goto error; }
75
76      /* k > 1 ? */
77      if (mp_cmp_d(k, 1) != LTC_MP_GT)                                                 { goto retry; }
78
79      /* test gcd */
80      if ((err = mp_gcd(k, key->q, tmp)) != CRYPT_OK)                                  { goto error; }
81   } while (mp_cmp_d(tmp, 1) != LTC_MP_EQ);
82
83   /* now find 1/k mod q */
84   if ((err = mp_invmod(k, key->q, kinv)) != CRYPT_OK)                                 { goto error; }
85
86   /* now find r = g^k mod p mod q */
87   if ((err = mp_exptmod(key->g, k, key->p, r)) != CRYPT_OK)                           { goto error; }
88   if ((err = mp_mod(r, key->q, r)) != CRYPT_OK)                                       { goto error; }
89
90   if (mp_iszero(r) == LTC_MP_YES)                                                     { goto retry; }
91
92   /* now find s = (in + xr)/k mod q */
93   if ((err = mp_read_unsigned_bin(tmp, (unsigned char *)in, inlen)) != CRYPT_OK)      { goto error; }
94   if ((err = mp_mul(key->x, r, s)) != CRYPT_OK)                                       { goto error; }
95   if ((err = mp_add(s, tmp, s)) != CRYPT_OK)                                          { goto error; }
96   if ((err = mp_mulmod(s, kinv, key->q, s)) != CRYPT_OK)                              { goto error; }
97
98   if (mp_iszero(s) == LTC_MP_YES)                                                     { goto retry; }
99
100   err = CRYPT_OK;
101error:
102   mp_clear_multi(k, kinv, tmp, NULL);
103ERRBUF:
104#ifdef LTC_CLEAN_STACK
105   zeromem(buf, MDSA_MAX_GROUP);
106#endif
107   XFREE(buf);
108   return err;
109}
110
111/**
112  Sign a hash with DSA
113  @param in       The hash to sign
114  @param inlen    The length of the hash to sign
115  @param out      [out] Where to store the signature
116  @param outlen   [in/out] The max size and resulting size of the signature
117  @param prng     An active PRNG state
118  @param wprng    The index of the PRNG desired
119  @param key      A private DSA key
120  @return CRYPT_OK if successful
121*/
122int dsa_sign_hash(const unsigned char *in,  unsigned long inlen,
123                        unsigned char *out, unsigned long *outlen,
124                        prng_state *prng, int wprng, dsa_key *key)
125{
126   void         *r, *s;
127   int           err;
128
129   LTC_ARGCHK(in      != NULL);
130   LTC_ARGCHK(out     != NULL);
131   LTC_ARGCHK(outlen  != NULL);
132   LTC_ARGCHK(key     != NULL);
133
134   if (mp_init_multi(&r, &s, NULL) != CRYPT_OK) {
135      return CRYPT_MEM;
136   }
137
138   if ((err = dsa_sign_hash_raw(in, inlen, r, s, prng, wprng, key)) != CRYPT_OK) {
139      goto error;
140   }
141
142   err = der_encode_sequence_multi(out, outlen,
143                             LTC_ASN1_INTEGER, 1UL, r,
144                             LTC_ASN1_INTEGER, 1UL, s,
145                             LTC_ASN1_EOL,     0UL, NULL);
146
147error:
148   mp_clear_multi(r, s, NULL);
149   return err;
150}
151
152#endif
153
154/* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_sign_hash.c,v $ */
155/* $Revision: 1.12 $ */
156/* $Date: 2006/12/04 22:27:56 $ */
157