78 lines
2.0 KiB
C
78 lines
2.0 KiB
C
/* LibTomCrypt, modular cryptographic library -- Tom St Denis
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*
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* LibTomCrypt is a library that provides various cryptographic
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* algorithms in a highly modular and flexible manner.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tomstdenis@iahu.ca, http://libtomcrypt.org
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*/
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#include "mycrypt.h"
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/* PKCS #1 v1.5 Signature Padding -- Tom St Denis */
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#ifdef PKCS_1
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int pkcs_1_v15_sa_decode(const unsigned char *msghash, unsigned long msghashlen,
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const unsigned char *sig, unsigned long siglen,
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int hash_idx, unsigned long modulus_bitlen,
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int *res)
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{
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unsigned long x, y, modulus_bytelen, derlen;
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int err;
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_ARGCHK(msghash != NULL);
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_ARGCHK(sig != NULL);
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_ARGCHK(res != NULL);
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/* default to invalid */
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*res = 0;
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/* valid hash ? */
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if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
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return err;
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}
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/* get derlen */
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derlen = hash_descriptor[hash_idx].DERlen;
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/* get modulus len */
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modulus_bytelen = (modulus_bitlen>>3) + (modulus_bitlen & 7 ? 1 : 0);
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/* valid sizes? */
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if ((msghashlen + 3 + derlen > modulus_bytelen) || (siglen != modulus_bytelen)) {
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return CRYPT_PK_INVALID_SIZE;
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}
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/* packet is 0x00 0x01 PS 0x00 T, where PS == 0xFF repeated modulus_bytelen - 3 - derlen - msghashlen times, T == DER || hash */
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x = 0;
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if (sig[x++] != 0x00 || sig[x++] != 0x01) {
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return CRYPT_OK;
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}
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/* now follows (modulus_bytelen - 3 - derlen - msghashlen) 0xFF bytes */
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for (y = 0; y < (modulus_bytelen - 3 - derlen - msghashlen); y++) {
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if (sig[x++] != 0xFF) {
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return CRYPT_OK;
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}
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}
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if (sig[x++] != 0x00) {
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return CRYPT_OK;
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}
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for (y = 0; y < derlen; y++) {
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if (sig[x++] != hash_descriptor[hash_idx].DER[y]) {
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return CRYPT_OK;
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}
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}
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if (memcmp(msghash, sig+x, msghashlen) == 0) {
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*res = 1;
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}
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return CRYPT_OK;
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}
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#endif
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