| /* LibTomCrypt, modular cryptographic library -- Tom St Denis |
| * |
| * LibTomCrypt is a library that provides various cryptographic |
| * algorithms in a highly modular and flexible manner. |
| * |
| * The library is free for all purposes without any express |
| * guarantee it works. |
| * |
| * Tom St Denis, tomstdenis@iahu.ca, http://libtomcrypt.org |
| */ |
| #include "mycrypt.h" |
| |
| /* PKCS #1 v1.5 Encryption Padding -- Tom St Denis */ |
| |
| #ifdef PKCS_1 |
| |
| int pkcs_1_v15_es_decode(const unsigned char *msg, unsigned long msglen, |
| unsigned long modulus_bitlen, |
| unsigned char *out, unsigned long outlen, |
| int *res) |
| { |
| unsigned long x, modulus_bytelen; |
| |
| _ARGCHK(msg != NULL); |
| _ARGCHK(out != NULL); |
| _ARGCHK(res != NULL); |
| |
| /* default to failed */ |
| *res = 0; |
| |
| /* must be at least 12 bytes long */ |
| if (msglen < 12) { |
| return CRYPT_INVALID_ARG; |
| } |
| |
| modulus_bytelen = (modulus_bitlen>>3) + (modulus_bitlen & 7 ? 1 : 0); |
| |
| /* should start with 0x00 0x02 */ |
| if (msg[0] != 0x00 || msg[1] != 0x02) { |
| return CRYPT_OK; |
| } |
| |
| /* skip over PS */ |
| x = 2 + (modulus_bytelen - outlen - 3); |
| |
| /* should be 0x00 */ |
| if (msg[x++] != 0x00) { |
| return CRYPT_OK; |
| } |
| |
| /* the message is left */ |
| if (x + outlen > modulus_bytelen) { |
| return CRYPT_PK_INVALID_SIZE; |
| } |
| memcpy(out, msg + x, outlen); |
| *res = 1; |
| return CRYPT_OK; |
| } |
| |
| #endif |
| |