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109 lines
2.4 KiB
C
109 lines
2.4 KiB
C
/* LibTomCrypt, modular cryptographic library -- Tom St Denis
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*
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* LibTomCrypt is a library that provides various cryptographic
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* algorithms in a highly modular and flexible manner.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*/
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#include "tomcrypt.h"
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/**
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@file der_decode_integer.c
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ASN.1 DER, decode an integer, Tom St Denis
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*/
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#ifdef LTC_DER
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/**
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Read a mp_int integer
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@param in The DER encoded data
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@param inlen Size of DER encoded data
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@param num The first mp_int to decode
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@return CRYPT_OK if successful
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*/
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int der_decode_integer(const unsigned char *in, unsigned long inlen, void *num)
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{
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unsigned long x, y, z;
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int err;
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LTC_ARGCHK(num != NULL);
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LTC_ARGCHK(in != NULL);
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/* min DER INTEGER is 0x02 01 00 == 0 */
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if (inlen < (1 + 1 + 1)) {
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return CRYPT_INVALID_PACKET;
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}
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/* ok expect 0x02 when we AND with 0001 1111 [1F] */
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x = 0;
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if ((in[x++] & 0x1F) != 0x02) {
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return CRYPT_INVALID_PACKET;
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}
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/* now decode the len stuff */
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z = in[x++];
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if ((z & 0x80) == 0x00) {
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/* short form */
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/* will it overflow? */
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if (x + z > inlen) {
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return CRYPT_INVALID_PACKET;
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}
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/* no so read it */
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if ((err = mp_read_unsigned_bin(num, (unsigned char *)in + x, z)) != CRYPT_OK) {
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return err;
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}
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} else {
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/* long form */
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z &= 0x7F;
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/* will number of length bytes overflow? (or > 4) */
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if (((x + z) > inlen) || (z > 4) || (z == 0)) {
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return CRYPT_INVALID_PACKET;
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}
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/* now read it in */
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y = 0;
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while (z--) {
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y = ((unsigned long)(in[x++])) | (y << 8);
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}
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/* now will reading y bytes overrun? */
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if ((x + y) > inlen) {
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return CRYPT_INVALID_PACKET;
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}
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/* no so read it */
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if ((err = mp_read_unsigned_bin(num, (unsigned char *)in + x, y)) != CRYPT_OK) {
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return err;
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}
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}
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/* see if it's negative */
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if (in[x] & 0x80) {
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void *tmp;
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if (mp_init(&tmp) != CRYPT_OK) {
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return CRYPT_MEM;
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}
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if (mp_2expt(tmp, mp_count_bits(num)) != CRYPT_OK || mp_sub(num, tmp, num) != CRYPT_OK) {
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mp_clear(tmp);
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return CRYPT_MEM;
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}
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mp_clear(tmp);
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}
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return CRYPT_OK;
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}
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#endif
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/* ref: HEAD -> master, tag: v1.18.2 */
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/* git commit: 7e7eb695d581782f04b24dc444cbfde86af59853 */
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/* commit time: 2018-07-01 22:49:01 +0200 */
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