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
12/* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b
13 *
14 * All curves taken from NIST recommendation paper of July 1999
15 * Available at http://csrc.nist.gov/cryptval/dss.htm
16 */
17#include "tomcrypt.h"
18
19/**
20  @file ecc_verify_hash.c
21  ECC Crypto, Tom St Denis
22*/
23
24#ifdef MECC
25
26/* verify
27 *
28 * w  = s^-1 mod n
29 * u1 = xw
30 * u2 = rw
31 * X = u1*G + u2*Q
32 * v = X_x1 mod n
33 * accept if v == r
34 */
35
36/**
37   Verify an ECC signature
38   @param sig         The signature to verify
39   @param siglen      The length of the signature (octets)
40   @param hash        The hash (message digest) that was signed
41   @param hashlen     The length of the hash (octets)
42   @param stat        Result of signature, 1==valid, 0==invalid
43   @param key         The corresponding public ECC key
44   @return CRYPT_OK if successful (even if the signature is not valid)
45*/
46int ecc_verify_hash(const unsigned char *sig,  unsigned long siglen,
47                    const unsigned char *hash, unsigned long hashlen,
48                    int *stat, ecc_key *key)
49{
50   ecc_point    *mG, *mQ;
51   void          *r, *s, *v, *w, *u1, *u2, *e, *p, *m;
52   void          *mp;
53   int           err;
54
55   LTC_ARGCHK(sig  != NULL);
56   LTC_ARGCHK(hash != NULL);
57   LTC_ARGCHK(stat != NULL);
58   LTC_ARGCHK(key  != NULL);
59
60   /* default to invalid signature */
61   *stat = 0;
62   mp    = NULL;
63
64   /* is the IDX valid ?  */
65   if (ltc_ecc_is_valid_idx(key->idx) != 1) {
66      return CRYPT_PK_INVALID_TYPE;
67   }
68
69   /* allocate ints */
70   if ((err = mp_init_multi(&r, &s, &v, &w, &u1, &u2, &p, &e, &m, NULL)) != CRYPT_OK) {
71      return CRYPT_MEM;
72   }
73
74   /* allocate points */
75   mG = ltc_ecc_new_point();
76   mQ = ltc_ecc_new_point();
77   if (mQ  == NULL || mG == NULL) {
78      err = CRYPT_MEM;
79      goto error;
80   }
81
82   /* parse header */
83   if ((err = der_decode_sequence_multi(sig, siglen,
84                                  LTC_ASN1_INTEGER, 1UL, r,
85                                  LTC_ASN1_INTEGER, 1UL, s,
86                                  LTC_ASN1_EOL, 0UL, NULL)) != CRYPT_OK) {
87      goto error;
88   }
89
90   /* get the order */
91   if ((err = mp_read_radix(p, (char *)key->dp->order, 16)) != CRYPT_OK)                                { goto error; }
92
93   /* get the modulus */
94   if ((err = mp_read_radix(m, (char *)key->dp->prime, 16)) != CRYPT_OK)                                { goto error; }
95
96   /* check for zero */
97   if (mp_iszero(r) || mp_iszero(s) || mp_cmp(r, p) != LTC_MP_LT || mp_cmp(s, p) != LTC_MP_LT) {
98      err = CRYPT_INVALID_PACKET;
99      goto error;
100   }
101
102   /* read hash */
103   if ((err = mp_read_unsigned_bin(e, (unsigned char *)hash, (int)hashlen)) != CRYPT_OK)                { goto error; }
104
105   /*  w  = s^-1 mod n */
106   if ((err = mp_invmod(s, p, w)) != CRYPT_OK)                                                          { goto error; }
107
108   /* u1 = ew */
109   if ((err = mp_mulmod(e, w, p, u1)) != CRYPT_OK)                                                      { goto error; }
110
111   /* u2 = rw */
112   if ((err = mp_mulmod(r, w, p, u2)) != CRYPT_OK)                                                      { goto error; }
113
114   /* find mG and mQ */
115   if ((err = mp_read_radix(mG->x, (char *)key->dp->Gx, 16)) != CRYPT_OK)                               { goto error; }
116   if ((err = mp_read_radix(mG->y, (char *)key->dp->Gy, 16)) != CRYPT_OK)                               { goto error; }
117   if ((err = mp_set(mG->z, 1)) != CRYPT_OK)                                                            { goto error; }
118
119   if ((err = mp_copy(key->pubkey.x, mQ->x)) != CRYPT_OK)                                               { goto error; }
120   if ((err = mp_copy(key->pubkey.y, mQ->y)) != CRYPT_OK)                                               { goto error; }
121   if ((err = mp_copy(key->pubkey.z, mQ->z)) != CRYPT_OK)                                               { goto error; }
122
123   /* compute u1*mG + u2*mQ = mG */
124   if (ltc_mp.ecc_mul2add == NULL) {
125      if ((err = ltc_mp.ecc_ptmul(u1, mG, mG, m, 0)) != CRYPT_OK)                                       { goto error; }
126      if ((err = ltc_mp.ecc_ptmul(u2, mQ, mQ, m, 0)) != CRYPT_OK)                                       { goto error; }
127
128      /* find the montgomery mp */
129      if ((err = mp_montgomery_setup(m, &mp)) != CRYPT_OK)                                              { goto error; }
130
131      /* add them */
132      if ((err = ltc_mp.ecc_ptadd(mQ, mG, mG, m, mp)) != CRYPT_OK)                                      { goto error; }
133
134      /* reduce */
135      if ((err = ltc_mp.ecc_map(mG, m, mp)) != CRYPT_OK)                                                { goto error; }
136   } else {
137      /* use Shamir's trick to compute u1*mG + u2*mQ using half of the doubles */
138      if ((err = ltc_mp.ecc_mul2add(mG, u1, mQ, u2, mG, m)) != CRYPT_OK)                                { goto error; }
139   }
140
141   /* v = X_x1 mod n */
142   if ((err = mp_mod(mG->x, p, v)) != CRYPT_OK)                                                         { goto error; }
143
144   /* does v == r */
145   if (mp_cmp(v, r) == LTC_MP_EQ) {
146      *stat = 1;
147   }
148
149   /* clear up and return */
150   err = CRYPT_OK;
151error:
152   ltc_ecc_del_point(mG);
153   ltc_ecc_del_point(mQ);
154   mp_clear_multi(r, s, v, w, u1, u2, p, e, m, NULL);
155   if (mp != NULL) {
156      mp_montgomery_free(mp);
157   }
158   return err;
159}
160
161#endif
162/* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ecc_verify_hash.c,v $ */
163/* $Revision: 1.12 $ */
164/* $Date: 2006/12/04 05:07:59 $ */
165
166