1 // SPDX-License-Identifier: BSD-2-Clause
2 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
3 *
4 * LibTomCrypt is a library that provides various cryptographic
5 * algorithms in a highly modular and flexible manner.
6 *
7 * The library is free for all purposes without any express
8 * guarantee it works.
9 */
10 #include "tomcrypt_private.h"
11
12 /**
13 @file der_decode_integer.c
14 ASN.1 DER, decode an integer, Tom St Denis
15 */
16
17
18 #ifdef LTC_DER
19
20 /**
21 Read a mp_int integer
22 @param in The DER encoded data
23 @param inlen Size of DER encoded data
24 @param num The first mp_int to decode
25 @return CRYPT_OK if successful
26 */
der_decode_integer(const unsigned char * in,unsigned long inlen,void * num)27 int der_decode_integer(const unsigned char *in, unsigned long inlen, void *num)
28 {
29 unsigned long x, y;
30 int err;
31
32 LTC_ARGCHK(num != NULL);
33 LTC_ARGCHK(in != NULL);
34
35 /* min DER INTEGER is 0x02 01 00 == 0 */
36 if (inlen < (1 + 1 + 1)) {
37 return CRYPT_INVALID_PACKET;
38 }
39
40 /* ok expect 0x02 when we AND with 0001 1111 [1F] */
41 x = 0;
42 if ((in[x++] & 0x1F) != 0x02) {
43 return CRYPT_INVALID_PACKET;
44 }
45
46 /* get the length of the data */
47 inlen -= x;
48 if ((err = der_decode_asn1_length(in + x, &inlen, &y)) != CRYPT_OK) {
49 return err;
50 }
51 x += inlen;
52
53 if ((err = mp_read_unsigned_bin(num, (unsigned char *)in + x, y)) != CRYPT_OK) {
54 return err;
55 }
56
57 /* see if it's negative */
58 if (in[x] & 0x80) {
59 void *tmp;
60 if (mp_init(&tmp) != CRYPT_OK) {
61 return CRYPT_MEM;
62 }
63
64 if (mp_2expt(tmp, mp_count_bits(num)) != CRYPT_OK || mp_sub(num, tmp, num) != CRYPT_OK) {
65 mp_clear(tmp);
66 return CRYPT_MEM;
67 }
68 mp_clear(tmp);
69 }
70
71 return CRYPT_OK;
72
73 }
74
75 #endif
76
77 /* ref: $Format:%D$ */
78 /* git commit: $Format:%H$ */
79 /* commit time: $Format:%ai$ */
80