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comparison libtomcrypt/src/pk/asn1/der/integer/der_length_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_length_integer.c
15 ASN.1 DER, get length of encoding, Tom St Denis
16 */
17
18
19 #ifdef LTC_DER
20 /**
21 Gets length of DER encoding of num
22 @param num The mp_int to get the size of
23 @param outlen [out] The length of the DER encoding for the given integer
24 @return CRYPT_OK if successful
25 */
26 int der_length_integer(mp_int *num, unsigned long *outlen)
27 {
28 unsigned long z, len;
29 int leading_zero;
30
31 LTC_ARGCHK(num != NULL);
32 LTC_ARGCHK(outlen != NULL);
33
34 if (mp_cmp_d(num, 0) != MP_LT) {
35 /* positive */
36
37 /* we only need a leading zero if the msb of the first byte is one */
38 if ((mp_count_bits(num) & 7) == 0 || mp_iszero(num) == MP_YES) {
39 leading_zero = 1;
40 } else {
41 leading_zero = 0;
42 }
43
44 /* size for bignum */
45 z = len = leading_zero + mp_unsigned_bin_size(num);
46 } else {
47 /* it's negative */
48 /* find power of 2 that is a multiple of eight and greater than count bits */
49 leading_zero = 0;
50 z = mp_count_bits(num);
51 z = z + (8 - (z & 7));
52 len = z = z >> 3;
53 }
54
55 /* now we need a length */
56 if (z < 128) {
57 /* short form */
58 ++len;
59 } else {
60 /* long form (relies on z != 0), assumes length bytes < 128 */
61 ++len;
62
63 while (z) {
64 ++len;
65 z >>= 8;
66 }
67 }
68
69 /* we need a 0x02 to indicate it's INTEGER */
70 ++len;
71
72 /* return length */
73 *outlen = len;
74 return CRYPT_OK;
75 }
76
77 #endif
78
79 /* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/integer/der_length_integer.c,v $ */
80 /* $Revision: 1.1 $ */
81 /* $Date: 2005/05/16 15:08:11 $ */