diff options
Diffstat (limited to 'src/pk/dsa/dsa_decrypt_key.c')
| -rw-r--r-- | src/pk/dsa/dsa_decrypt_key.c | 139 |
1 files changed, 139 insertions, 0 deletions
diff --git a/src/pk/dsa/dsa_decrypt_key.c b/src/pk/dsa/dsa_decrypt_key.c new file mode 100644 index 0000000..5cbedc6 --- /dev/null +++ b/src/pk/dsa/dsa_decrypt_key.c @@ -0,0 +1,139 @@ +/* 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.com + */ +#include "tomcrypt.h" + +/** + @file dsa_decrypt_key.c + DSA Crypto, Tom St Denis +*/ + +#ifdef MDSA + +/** + Decrypt an DSA encrypted key + @param in The ciphertext + @param inlen The length of the ciphertext (octets) + @param out [out] The plaintext + @param outlen [in/out] The max size and resulting size of the plaintext + @param key The corresponding private DSA key + @return CRYPT_OK if successful +*/ +int dsa_decrypt_key(const unsigned char *in, unsigned long inlen, + unsigned char *out, unsigned long *outlen, + dsa_key *key) +{ + unsigned char *skey, *expt; + void *g_pub; + unsigned long x, y, hashOID[32]; + int hash, err; + ltc_asn1_list decode[3]; + + LTC_ARGCHK(in != NULL); + LTC_ARGCHK(out != NULL); + LTC_ARGCHK(outlen != NULL); + LTC_ARGCHK(key != NULL); + + /* right key type? */ + if (key->type != PK_PRIVATE) { + return CRYPT_PK_NOT_PRIVATE; + } + + /* decode to find out hash */ + LTC_SET_ASN1(decode, 0, LTC_ASN1_OBJECT_IDENTIFIER, hashOID, sizeof(hashOID)/sizeof(hashOID[0])); + + if ((err = der_decode_sequence(in, inlen, decode, 1)) != CRYPT_OK) { + return err; + } + + hash = find_hash_oid(hashOID, decode[0].size); + if (hash_is_valid(hash) != CRYPT_OK) { + return CRYPT_INVALID_PACKET; + } + + /* we now have the hash! */ + + if ((err = mp_init(&g_pub)) != CRYPT_OK) { + return err; + } + + /* allocate memory */ + expt = XMALLOC(mp_unsigned_bin_size(key->p) + 1); + skey = XMALLOC(MAXBLOCKSIZE); + if (expt == NULL || skey == NULL) { + if (expt != NULL) { + XFREE(expt); + } + if (skey != NULL) { + XFREE(skey); + } + mp_clear(g_pub); + return CRYPT_MEM; + } + + LTC_SET_ASN1(decode, 1, LTC_ASN1_INTEGER, g_pub, 1UL); + LTC_SET_ASN1(decode, 2, LTC_ASN1_OCTET_STRING, skey, MAXBLOCKSIZE); + + /* read the structure in now */ + if ((err = der_decode_sequence(in, inlen, decode, 3)) != CRYPT_OK) { + goto LBL_ERR; + } + + /* make shared key */ + x = mp_unsigned_bin_size(key->p) + 1; + if ((err = dsa_shared_secret(key->x, g_pub, key, expt, &x)) != CRYPT_OK) { + goto LBL_ERR; + } + + y = MIN(mp_unsigned_bin_size(key->p) + 1, MAXBLOCKSIZE); + if ((err = hash_memory(hash, expt, x, expt, &y)) != CRYPT_OK) { + goto LBL_ERR; + } + + /* ensure the hash of the shared secret is at least as big as the encrypt itself */ + if (decode[2].size > y) { + err = CRYPT_INVALID_PACKET; + goto LBL_ERR; + } + + /* avoid buffer overflow */ + if (*outlen < decode[2].size) { + *outlen = decode[2].size; + err = CRYPT_BUFFER_OVERFLOW; + goto LBL_ERR; + } + + /* Decrypt the key */ + for (x = 0; x < decode[2].size; x++) { + out[x] = expt[x] ^ skey[x]; + } + *outlen = x; + + err = CRYPT_OK; +LBL_ERR: +#ifdef LTC_CLEAN_STACK + zeromem(expt, mp_unsigned_bin_size(key->p) + 1); + zeromem(skey, MAXBLOCKSIZE); +#endif + + XFREE(expt); + XFREE(skey); + + mp_clear(g_pub); + + return err; +} + +#endif + +/* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_decrypt_key.c,v $ */ +/* $Revision: 1.9 $ */ +/* $Date: 2006/12/04 03:18:43 $ */ + |