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comparison src/pk/asn1/der/short_integer/der_encode_short_integer.c @ 280:59400faa4b44 libtomcrypt-orig libtomcrypt-1.05

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Re-import libtomcrypt 1.05 for cleaner propagating. From crypt-1.05.tar.bz2, SHA1 of 88250202bb51570dc64f7e8f1c943cda9479258f
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 12:58:00 +0000
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children d5faf4814ddb
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-1:000000000000 280:59400faa4b44
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_encode_short_integer.c
15 ASN.1 DER, encode an integer, Tom St Denis
16 */
17
18
19 #ifdef LTC_DER
20
21 /* Exports a positive integer as DER format (upto 32-bits in size) */
22 /**
23 Store a mp_int integer
24 @param num The integer to encode
25 @param out [out] The destination for the DER encoded integers
26 @param outlen [in/out] The max size and resulting size of the DER encoded integers
27 @return CRYPT_OK if successful
28 */
29 int der_encode_short_integer(unsigned long num, unsigned char *out, unsigned long *outlen)
30 {
31 unsigned long len, x, y, z;
32 int err;
33
34 LTC_ARGCHK(out != NULL);
35 LTC_ARGCHK(outlen != NULL);
36
37 /* force to 32 bits */
38 num &= 0xFFFFFFFFUL;
39
40 /* find out how big this will be */
41 if ((err = der_length_short_integer(num, &len)) != CRYPT_OK) {
42 return err;
43 }
44
45 if (*outlen < len) {
46 return CRYPT_BUFFER_OVERFLOW;
47 }
48
49 /* get len of output */
50 z = 0;
51 y = num;
52 while (y) {
53 ++z;
54 y >>= 8;
55 }
56
57 /* handle zero */
58 if (z == 0) {
59 z = 1;
60 }
61
62 /* see if msb is set */
63 z += (num&(1UL<<((z<<3) - 1))) ? 1 : 0;
64
65 /* adjust the number so the msB is non-zero */
66 for (x = 0; (z <= 4) && (x < (4 - z)); x++) {
67 num <<= 8;
68 }
69
70 /* store header */
71 x = 0;
72 out[x++] = 0x02;
73 out[x++] = z;
74
75 /* if 31st bit is set output a leading zero and decrement count */
76 if (z == 5) {
77 out[x++] = 0;
78 --z;
79 }
80
81 /* store values */
82 for (y = 0; y < z; y++) {
83 out[x++] = (num >> 24) & 0xFF;
84 num <<= 8;
85 }
86
87 /* we good */
88 *outlen = x;
89
90 return CRYPT_OK;
91 }
92
93 #endif
94
95 /* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/short_integer/der_encode_short_integer.c,v $ */
96 /* $Revision: 1.3 $ */
97 /* $Date: 2005/05/23 01:27:03 $ */