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, tomstdenis@gmail.com, http://libtomcrypt.com
10 */
11 #include "tomcrypt.h"
12
13 /**
14 @file der_length_short_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 integer 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 */
der_length_short_integer(unsigned long num,unsigned long * outlen)26 int der_length_short_integer(unsigned long num, unsigned long *outlen)
27 {
28 unsigned long z, y, len;
29
30 LTC_ARGCHK(outlen != NULL);
31
32 /* force to 32 bits */
33 num &= 0xFFFFFFFFUL;
34
35 /* get the number of bytes */
36 z = 0;
37 y = num;
38 while (y) {
39 ++z;
40 y >>= 8;
41 }
42
43 /* handle zero */
44 if (z == 0) {
45 z = 1;
46 }
47
48 /* we need a 0x02 to indicate it's INTEGER */
49 len = 1;
50
51 /* length byte */
52 ++len;
53
54 /* bytes in value */
55 len += z;
56
57 /* see if msb is set */
58 len += (num&(1UL<<((z<<3) - 1))) ? 1 : 0;
59
60 /* return length */
61 *outlen = len;
62
63 return CRYPT_OK;
64 }
65
66 #endif
67
68 /* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/short_integer/der_length_short_integer.c,v $ */
69 /* $Revision: 1.5 $ */
70 /* $Date: 2006/03/31 14:15:35 $ */
71