diff options
Diffstat (limited to 'src/pk/pkcs1/pkcs_1_oaep_decode.c')
| -rw-r--r-- | src/pk/pkcs1/pkcs_1_oaep_decode.c | 188 |
1 files changed, 188 insertions, 0 deletions
diff --git a/src/pk/pkcs1/pkcs_1_oaep_decode.c b/src/pk/pkcs1/pkcs_1_oaep_decode.c new file mode 100644 index 0000000..cd4931b --- /dev/null +++ b/src/pk/pkcs1/pkcs_1_oaep_decode.c @@ -0,0 +1,188 @@ +/* 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@gmail.com, http://libtomcrypt.org + */ +#include "tomcrypt.h" + +/** + @file pkcs_1_oaep_decode.c + OAEP Padding for PKCS #1, Tom St Denis +*/ + +#ifdef PKCS_1 + +/** + PKCS #1 v2.00 OAEP decode + @param msg The encoded data to decode + @param msglen The length of the encoded data (octets) + @param lparam The session or system data (can be NULL) + @param lparamlen The length of the lparam + @param modulus_bitlen The bit length of the RSA modulus + @param hash_idx The index of the hash desired + @param out [out] Destination of decoding + @param outlen [in/out] The max size and resulting size of the decoding + @param res [out] Result of decoding, 1==valid, 0==invalid + @return CRYPT_OK if successful (even if invalid) +*/ +int pkcs_1_oaep_decode(const unsigned char *msg, unsigned long msglen, + const unsigned char *lparam, unsigned long lparamlen, + unsigned long modulus_bitlen, int hash_idx, + unsigned char *out, unsigned long *outlen, + int *res) +{ + unsigned char *DB, *seed, *mask; + unsigned long hLen, x, y, modulus_len; + int err; + + LTC_ARGCHK(msg != NULL); + LTC_ARGCHK(out != NULL); + LTC_ARGCHK(outlen != NULL); + LTC_ARGCHK(res != NULL); + + /* default to invalid packet */ + *res = 0; + + /* test valid hash */ + if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) { + return err; + } + hLen = hash_descriptor[hash_idx].hashsize; + modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0); + + /* test hash/message size */ + if ((2*hLen >= (modulus_len - 2)) || (msglen != modulus_len)) { + return CRYPT_PK_INVALID_SIZE; + } + + /* allocate ram for DB/mask/salt of size modulus_len */ + DB = XMALLOC(modulus_len); + mask = XMALLOC(modulus_len); + seed = XMALLOC(hLen); + if (DB == NULL || mask == NULL || seed == NULL) { + if (DB != NULL) { + XFREE(DB); + } + if (mask != NULL) { + XFREE(mask); + } + if (seed != NULL) { + XFREE(seed); + } + return CRYPT_MEM; + } + + /* ok so it's now in the form + + 0x00 || maskedseed || maskedDB + + 1 || hLen || modulus_len - hLen - 1 + + */ + + /* must have leading 0x00 byte */ + if (msg[0] != 0x00) { + err = CRYPT_OK; + goto LBL_ERR; + } + + /* now read the masked seed */ + x = 1; + XMEMCPY(seed, msg + x, hLen); + x += hLen; + + /* now read the masked DB */ + XMEMCPY(DB, msg + x, modulus_len - hLen - 1); + x += modulus_len - hLen - 1; + + /* compute MGF1 of maskedDB (hLen) */ + if ((err = pkcs_1_mgf1(DB, modulus_len - hLen - 1, hash_idx, mask, hLen)) != CRYPT_OK) { + goto LBL_ERR; + } + + /* XOR against seed */ + for (y = 0; y < hLen; y++) { + seed[y] ^= mask[y]; + } + + /* compute MGF1 of seed (k - hlen - 1) */ + if ((err = pkcs_1_mgf1(seed, hLen, hash_idx, mask, modulus_len - hLen - 1)) != CRYPT_OK) { + goto LBL_ERR; + } + + /* xor against DB */ + for (y = 0; y < (modulus_len - hLen - 1); y++) { + DB[y] ^= mask[y]; + } + + /* now DB == lhash || PS || 0x01 || M, PS == k - mlen - 2hlen - 2 zeroes */ + + /* compute lhash and store it in seed [reuse temps!] */ + x = modulus_len; + if (lparam != NULL) { + if ((err = hash_memory(hash_idx, lparam, lparamlen, seed, &x)) != CRYPT_OK) { + goto LBL_ERR; + } + } else { + /* can't pass hash_memory a NULL so use DB with zero length */ + if ((err = hash_memory(hash_idx, DB, 0, seed, &x)) != CRYPT_OK) { + goto LBL_ERR; + } + } + + /* compare the lhash'es */ + if (memcmp(seed, DB, hLen) != 0) { + err = CRYPT_OK; + goto LBL_ERR; + } + + /* now zeroes before a 0x01 */ + for (x = hLen; x < (modulus_len - hLen - 1) && DB[x] == 0x00; x++) { + /* step... */ + } + + /* error out if wasn't 0x01 */ + if (x == (modulus_len - hLen - 1) || DB[x] != 0x01) { + err = CRYPT_OK; + goto LBL_ERR; + } + + /* rest is the message (and skip 0x01) */ + if ((modulus_len - hLen - 1) - ++x > *outlen) { + err = CRYPT_BUFFER_OVERFLOW; + goto LBL_ERR; + } + + /* copy message */ + *outlen = (modulus_len - hLen - 1) - x; + XMEMCPY(out, DB + x, modulus_len - hLen - 1 - x); + x += modulus_len - hLen - 1; + + /* valid packet */ + *res = 1; + + err = CRYPT_OK; +LBL_ERR: +#ifdef LTC_CLEAN_STACK + zeromem(DB, modulus_len); + zeromem(seed, hLen); + zeromem(mask, modulus_len); +#endif + + XFREE(seed); + XFREE(mask); + XFREE(DB); + + return err; +} + +#endif /* PKCS_1 */ + +/* $Source: /cvs/libtom/libtomcrypt/src/pk/pkcs1/pkcs_1_oaep_decode.c,v $ */ +/* $Revision: 1.5 $ */ +/* $Date: 2005/06/18 02:37:06 $ */ |