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comparison src/pk/asn1/der/der_length_integer.c @ 192:9cc34777b479 libtomcrypt

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propagate from branch 'au.asn.ucc.matt.ltc-orig' (head 9ba8f01f44320e9cb9f19881105ae84f84a43ea9) to branch 'au.asn.ucc.matt.dropbear.ltc' (head dbf51c569bc34956ad948e4cc87a0eeb2170b768)
author Matt Johnston <matt@ucc.asn.au>
date Sun, 08 May 2005 06:36:47 +0000
parents 1c15b283127b
children
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164:cd1143579f00 192:9cc34777b479
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 /* we only need a leading zero if the msb of the first byte is one */
35 if ((mp_count_bits(num) & 7) == 7 || mp_iszero(num) == MP_YES) {
36 leading_zero = 1;
37 } else {
38 leading_zero = 0;
39 }
40
41 /* size for bignum */
42 z = len = leading_zero + mp_unsigned_bin_size(num);
43
44 /* we need a 0x02 */
45 ++len;
46
47 /* now we need a length */
48 if (z < 128) {
49 /* short form */
50 ++len;
51 } else {
52 /* long form (relies on z != 0) */
53 ++len;
54
55 while (z) {
56 ++len;
57 z >>= 8;
58 }
59 }
60
61 *outlen = len;
62 return CRYPT_OK;
63 }
64
65 #endif