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Diffstat (limited to 'src/pk/katja/katja_decrypt_key.c')
| -rw-r--r-- | src/pk/katja/katja_decrypt_key.c | 105 |
1 files changed, 105 insertions, 0 deletions
diff --git a/src/pk/katja/katja_decrypt_key.c b/src/pk/katja/katja_decrypt_key.c new file mode 100644 index 0000000..1e10d6c --- /dev/null +++ b/src/pk/katja/katja_decrypt_key.c @@ -0,0 +1,105 @@ +/* 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 katja_decrypt_key.c + Katja PKCS #1 OAEP Decryption, Tom St Denis +*/ + +#ifdef MKAT + +/** + (PKCS #1 v2.0) decrypt then OAEP depad + @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 (octets) + @param lparam The system "lparam" value + @param lparamlen The length of the lparam value (octets) + @param hash_idx The index of the hash desired + @param stat [out] Result of the decryption, 1==valid, 0==invalid + @param key The corresponding private Katja key + @return CRYPT_OK if succcessul (even if invalid) +*/ +int katja_decrypt_key(const unsigned char *in, unsigned long inlen, + unsigned char *out, unsigned long *outlen, + const unsigned char *lparam, unsigned long lparamlen, + int hash_idx, int *stat, + katja_key *key) +{ + unsigned long modulus_bitlen, modulus_bytelen, x; + int err; + unsigned char *tmp; + + LTC_ARGCHK(out != NULL); + LTC_ARGCHK(outlen != NULL); + LTC_ARGCHK(key != NULL); + LTC_ARGCHK(stat != NULL); + + /* default to invalid */ + *stat = 0; + + /* valid hash ? */ + if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) { + return err; + } + + /* get modulus len in bits */ + modulus_bitlen = mp_count_bits( (key->N)); + + /* payload is upto pq, so we know q is 1/3rd the size of N and therefore pq is 2/3th the size */ + modulus_bitlen = ((modulus_bitlen << 1) / 3); + + /* round down to next byte */ + modulus_bitlen -= (modulus_bitlen & 7) + 8; + + /* outlen must be at least the size of the modulus */ + modulus_bytelen = mp_unsigned_bin_size( (key->N)); + if (modulus_bytelen != inlen) { + return CRYPT_INVALID_PACKET; + } + + /* allocate ram */ + tmp = XMALLOC(inlen); + if (tmp == NULL) { + return CRYPT_MEM; + } + + /* rsa decode the packet */ + x = inlen; + if ((err = katja_exptmod(in, inlen, tmp, &x, PK_PRIVATE, key)) != CRYPT_OK) { + XFREE(tmp); + return err; + } + + /* shift right by modulus_bytelen - modulus_bitlen/8 bytes */ + for (x = 0; x < (modulus_bitlen >> 3); x++) { + tmp[x] = tmp[x+(modulus_bytelen-(modulus_bitlen>>3))]; + } + + /* now OAEP decode the packet */ + err = pkcs_1_oaep_decode(tmp, x, lparam, lparamlen, modulus_bitlen, hash_idx, + out, outlen, stat); + + XFREE(tmp); + return err; +} + +#endif /* MRSA */ + + + + + +/* $Source: /cvs/libtom/libtomcrypt/src/pk/katja/katja_decrypt_key.c,v $ */ +/* $Revision: 1.4 $ */ +/* $Date: 2006/03/31 14:15:35 $ */ |