1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis 2 * 3 * LibTomCrypt is a library that provides various cryptographic 4 * algorithms in a highly modular and flexible manner. 5 * 6 * The library is free for all purposes without any express 7 * guarantee it works. 8 * 9 * Tom St Denis, tomstdenis (at) gmail.com, http://libtomcrypt.com 10 */ 11 #include "tomcrypt.h" 12 13 /** 14 @file katja_decrypt_key.c 15 Katja PKCS #1 OAEP Decryption, Tom St Denis 16 */ 17 18 #ifdef MKAT 19 20 /** 21 (PKCS #1 v2.0) decrypt then OAEP depad 22 @param in The ciphertext 23 @param inlen The length of the ciphertext (octets) 24 @param out [out] The plaintext 25 @param outlen [in/out] The max size and resulting size of the plaintext (octets) 26 @param lparam The system "lparam" value 27 @param lparamlen The length of the lparam value (octets) 28 @param hash_idx The index of the hash desired 29 @param stat [out] Result of the decryption, 1==valid, 0==invalid 30 @param key The corresponding private Katja key 31 @return CRYPT_OK if succcessul (even if invalid) 32 */ 33 int katja_decrypt_key(const unsigned char *in, unsigned long inlen, 34 unsigned char *out, unsigned long *outlen, 35 const unsigned char *lparam, unsigned long lparamlen, 36 int hash_idx, int *stat, 37 katja_key *key) 38 { 39 unsigned long modulus_bitlen, modulus_bytelen, x; 40 int err; 41 unsigned char *tmp; 42 43 LTC_ARGCHK(out != NULL); 44 LTC_ARGCHK(outlen != NULL); 45 LTC_ARGCHK(key != NULL); 46 LTC_ARGCHK(stat != NULL); 47 48 /* default to invalid */ 49 *stat = 0; 50 51 /* valid hash ? */ 52 if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) { 53 return err; 54 } 55 56 /* get modulus len in bits */ 57 modulus_bitlen = mp_count_bits( (key->N)); 58 59 /* payload is upto pq, so we know q is 1/3rd the size of N and therefore pq is 2/3th the size */ 60 modulus_bitlen = ((modulus_bitlen << 1) / 3); 61 62 /* round down to next byte */ 63 modulus_bitlen -= (modulus_bitlen & 7) + 8; 64 65 /* outlen must be at least the size of the modulus */ 66 modulus_bytelen = mp_unsigned_bin_size( (key->N)); 67 if (modulus_bytelen != inlen) { 68 return CRYPT_INVALID_PACKET; 69 } 70 71 /* allocate ram */ 72 tmp = XMALLOC(inlen); 73 if (tmp == NULL) { 74 return CRYPT_MEM; 75 } 76 77 /* rsa decode the packet */ 78 x = inlen; 79 if ((err = katja_exptmod(in, inlen, tmp, &x, PK_PRIVATE, key)) != CRYPT_OK) { 80 XFREE(tmp); 81 return err; 82 } 83 84 /* shift right by modulus_bytelen - modulus_bitlen/8 bytes */ 85 for (x = 0; x < (modulus_bitlen >> 3); x++) { 86 tmp[x] = tmp[x+(modulus_bytelen-(modulus_bitlen>>3))]; 87 } 88 89 /* now OAEP decode the packet */ 90 err = pkcs_1_oaep_decode(tmp, x, lparam, lparamlen, modulus_bitlen, hash_idx, 91 out, outlen, stat); 92 93 XFREE(tmp); 94 return err; 95 } 96 97 #endif /* MRSA */ 98 99 100 101 102 103 /* $Source: /cvs/libtom/libtomcrypt/src/pk/katja/katja_decrypt_key.c,v $ */ 104 /* $Revision: 1.4 $ */ 105 /* $Date: 2006/03/31 14:15:35 $ */ 106
