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comparison libtomcrypt/src/pk/asn1/der/integer/der_decode_integer.c @ 285:1b9e69c058d2

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propagate from branch 'au.asn.ucc.matt.ltc.dropbear' (head 20dccfc09627970a312d77fb41dc2970b62689c3) to branch 'au.asn.ucc.matt.dropbear' (head fdf4a7a3b97ae5046139915de7e40399cceb2c01)
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:23:58 +0000
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children 0cbe8f6dbf9e
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281:997e6f7dc01e 285:1b9e69c058d2
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, [email protected], http://libtomcrypt.org
10 */
11 #include "tomcrypt.h"
12
13 /**
14 @file der_decode_integer.c
15 ASN.1 DER, decode an integer, Tom St Denis
16 */
17
18
19 #ifdef LTC_DER
20
21 /**
22 Read a mp_int integer
23 @param in The DER encoded data
24 @param inlen Size of DER encoded data
25 @param num The first mp_int to decode
26 @return CRYPT_OK if successful
27 */
28 int der_decode_integer(const unsigned char *in, unsigned long inlen, mp_int *num)
29 {
30 unsigned long x, y, z;
31 int err;
32
33 LTC_ARGCHK(num != NULL);
34 LTC_ARGCHK(in != NULL);
35
36 /* min DER INTEGER is 0x02 01 00 == 0 */
37 if (inlen < (1 + 1 + 1)) {
38 return CRYPT_INVALID_PACKET;
39 }
40
41 /* ok expect 0x02 when we AND with 0001 1111 [1F] */
42 x = 0;
43 if ((in[x++] & 0x1F) != 0x02) {
44 return CRYPT_INVALID_PACKET;
45 }
46
47 /* now decode the len stuff */
48 z = in[x++];
49
50 if ((z & 0x80) == 0x00) {
51 /* short form */
52
53 /* will it overflow? */
54 if (x + z > inlen) {
55 return CRYPT_INVALID_PACKET;
56 }
57
58 /* no so read it */
59 if ((err = mpi_to_ltc_error(mp_read_unsigned_bin(num, (unsigned char *)in + x, z))) != CRYPT_OK) {
60 return err;
61 }
62 } else {
63 /* long form */
64 z &= 0x7F;
65
66 /* will number of length bytes overflow? (or > 4) */
67 if (((x + z) > inlen) || (z > 4) || (z == 0)) {
68 return CRYPT_INVALID_PACKET;
69 }
70
71 /* now read it in */
72 y = 0;
73 while (z--) {
74 y = ((unsigned long)(in[x++])) | (y << 8);
75 }
76
77 /* now will reading y bytes overrun? */
78 if ((x + y) > inlen) {
79 return CRYPT_INVALID_PACKET;
80 }
81
82 /* no so read it */
83 if ((err = mpi_to_ltc_error(mp_read_unsigned_bin(num, (unsigned char *)in + x, y))) != CRYPT_OK) {
84 return err;
85 }
86 }
87
88 /* see if it's negative */
89 if (in[x] & 0x80) {
90 mp_int tmp;
91 if (mp_init(&tmp) != MP_OKAY) {
92 return CRYPT_MEM;
93 }
94
95 if (mp_2expt(&tmp, mp_count_bits(num)) != MP_OKAY || mp_sub(num, &tmp, num) != MP_OKAY) {
96 mp_clear(&tmp);
97 return CRYPT_MEM;
98 }
99 mp_clear(&tmp);
100 }
101
102 return CRYPT_OK;
103
104 }
105
106 #endif
107
108 /* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/integer/der_decode_integer.c,v $ */
109 /* $Revision: 1.2 $ */
110 /* $Date: 2005/06/01 00:06:05 $ */