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/* 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.
*/
#include "tomcrypt.h"
/**
@file katja_decrypt_key.c
Katja PKCS #1 OAEP Decryption, Tom St Denis
*/
#ifdef LTC_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 /* LTC_MRSA */
/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */
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