Mercurial > dropbear

comparison libtomcrypt/src/pk/asn1/der/integer/der_length_integer.c @ 389:5ff8218bcee9

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 2af95f00ebd5bb7a28b3817db1218442c935388e) to branch 'au.asn.ucc.matt.dropbear' (head ecd779509ef23a8cdf64888904fc9b31d78aa933)
author Matt Johnston <matt@ucc.asn.au>
date Thu, 11 Jan 2007 03:14:55 +0000
parents 0cbe8f6dbf9e
children f849a5ca2efc
comparison
equal deleted inserted replaced
388:fb54020f78e1 389:5ff8218bcee9
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.com
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 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(void *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) != LTC_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) == LTC_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 if (((mp_cnt_lsb(num)+1)==mp_count_bits(num)) && ((mp_count_bits(num)&7)==0)) --z;
53 len = z = z >> 3;
54 }
55
56 /* now we need a length */
57 if (z < 128) {
58 /* short form */
59 ++len;
60 } else {
61 /* long form (relies on z != 0), assumes length bytes < 128 */
62 ++len;
63
64 while (z) {
65 ++len;
66 z >>= 8;
67 }
68 }
69
70 /* we need a 0x02 to indicate it's INTEGER */
71 ++len;
72
73 /* return length */
74 *outlen = len;
75 return CRYPT_OK;
76 }
77
78 #endif
79
80 /* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/integer/der_length_integer.c,v $ */
81 /* $Revision: 1.4 $ */
82 /* $Date: 2006/04/22 01:22:55 $ */