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comparison pkcs_1_v15_sa_decode.c @ 15:6362d3854bb4 libtomcrypt-orig

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0.96 release of LibTomCrypt
author Matt Johnston <matt@ucc.asn.au>
date Tue, 15 Jun 2004 14:07:21 +0000
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3:7faae8f46238 15:6362d3854bb4
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, [email protected], http://libtomcrypt.org
10 */
11 #include "mycrypt.h"
12
13 /* PKCS #1 v1.5 Signature Padding -- Tom St Denis */
14
15 #ifdef PKCS_1
16
17 int pkcs_1_v15_sa_decode(const unsigned char *msghash, unsigned long msghashlen,
18 const unsigned char *sig, unsigned long siglen,
19 int hash_idx, unsigned long modulus_bitlen,
20 int *res)
21 {
22 unsigned long x, y, modulus_bytelen, derlen;
23 int err;
24
25 _ARGCHK(msghash != NULL);
26 _ARGCHK(sig != NULL);
27 _ARGCHK(res != NULL);
28
29 /* default to invalid */
30 *res = 0;
31
32 /* valid hash ? */
33 if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
34 return err;
35 }
36
37 /* get derlen */
38 derlen = hash_descriptor[hash_idx].DERlen;
39
40 /* get modulus len */
41 modulus_bytelen = (modulus_bitlen>>3) + (modulus_bitlen & 7 ? 1 : 0);
42
43 /* valid sizes? */
44 if ((msghashlen + 3 + derlen > modulus_bytelen) || (siglen != modulus_bytelen)) {
45 return CRYPT_PK_INVALID_SIZE;
46 }
47
48 /* packet is 0x00 0x01 PS 0x00 T, where PS == 0xFF repeated modulus_bytelen - 3 - derlen - msghashlen times, T == DER || hash */
49 x = 0;
50 if (sig[x++] != 0x00 || sig[x++] != 0x01) {
51 return CRYPT_OK;
52 }
53
54 /* now follows (modulus_bytelen - 3 - derlen - msghashlen) 0xFF bytes */
55 for (y = 0; y < (modulus_bytelen - 3 - derlen - msghashlen); y++) {
56 if (sig[x++] != 0xFF) {
57 return CRYPT_OK;
58 }
59 }
60
61 if (sig[x++] != 0x00) {
62 return CRYPT_OK;
63 }
64
65 for (y = 0; y < derlen; y++) {
66 if (sig[x++] != hash_descriptor[hash_idx].DER[y]) {
67 return CRYPT_OK;
68 }
69 }
70
71 if (memcmp(msghash, sig+x, msghashlen) == 0) {
72 *res = 1;
73 }
74 return CRYPT_OK;
75 }
76
77 #endif