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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.
*
* Tom St Denis, tomstdenis@gmail.com, http://libtom.org
*/
#include "tomcrypt.h"
/**
@file der_decode_integer.c
ASN.1 DER, decode an integer, Tom St Denis
*/
#ifdef LTC_DER
/**
Read a mp_int integer
@param in The DER encoded data
@param inlen Size of DER encoded data
@param num The first mp_int to decode
@return CRYPT_OK if successful
*/
int der_decode_integer(const unsigned char *in, unsigned long inlen, mp_int_t num)
{
unsigned long x, y, z;
int err;
LTC_ARGCHK(num != NULL);
LTC_ARGCHK(in != NULL);
/* min DER INTEGER is 0x02 01 00 == 0 */
if (inlen < (1 + 1 + 1)) {
return CRYPT_INVALID_PACKET;
}
/* ok expect 0x02 when we AND with 0001 1111 [1F] */
x = 0;
if ((in[x++] & 0x1F) != 0x02) {
return CRYPT_INVALID_PACKET;
}
/* now decode the len stuff */
z = in[x++];
if ((z & 0x80) == 0x00) {
/* short form */
/* will it overflow? */
if (x + z > inlen) {
return CRYPT_INVALID_PACKET;
}
/* no so read it */
if ((err = mp_read_unsigned_bin(num, (unsigned char *)in + x, z)) != CRYPT_OK) {
return err;
}
} else {
/* long form */
z &= 0x7F;
/* will number of length bytes overflow? (or > 4) */
if (((x + z) > inlen) || (z > 4) || (z == 0)) {
return CRYPT_INVALID_PACKET;
}
/* now read it in */
y = 0;
while (z--) {
y = ((unsigned long)(in[x++])) | (y << 8);
}
/* now will reading y bytes overrun? */
if ((x + y) > inlen) {
return CRYPT_INVALID_PACKET;
}
/* no so read it */
if ((err = mp_read_unsigned_bin(num, (unsigned char *)in + x, y)) != CRYPT_OK) {
return err;
}
}
/* see if it's negative */
if (in[x] & 0x80) {
mp_int tmp;
if (mp_init(&tmp) != CRYPT_OK) {
return CRYPT_MEM;
}
if (mp_2expt(&tmp, mp_count_bits(num)) != CRYPT_OK || mp_sub(num, &tmp, num) != CRYPT_OK) {
mp_clear(&tmp);
return CRYPT_MEM;
}
mp_clear(&tmp);
}
return CRYPT_OK;
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/integer/der_decode_integer.c,v $ */
/* $Revision: 1.5 $ */
/* $Date: 2006/12/28 01:27:24 $ */
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