1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
|
/* LibTomCrypt, modular cryptographic library -- Tom St Denis
*
* LibTomCrypt is a library that provides various cryptographic
* algorithms in a highly modular and flexible manner.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.org
*/
#include "tomcrypt.h"
/**
@file der_encode_short_integer.c
ASN.1 DER, encode an integer, Tom St Denis
*/
#ifdef LTC_DER
/* Exports a positive integer as DER format (upto 32-bits in size) */
/**
Store a mp_int integer
@param num The integer to encode
@param out [out] The destination for the DER encoded integers
@param outlen [in/out] The max size and resulting size of the DER encoded integers
@return CRYPT_OK if successful
*/
int der_encode_short_integer(unsigned long num, unsigned char *out, unsigned long *outlen)
{
unsigned long len, x, y, z;
int err;
LTC_ARGCHK(out != NULL);
LTC_ARGCHK(outlen != NULL);
/* force to 32 bits */
num &= 0xFFFFFFFFUL;
/* find out how big this will be */
if ((err = der_length_short_integer(num, &len)) != CRYPT_OK) {
return err;
}
if (*outlen < len) {
return CRYPT_BUFFER_OVERFLOW;
}
/* get len of output */
z = 0;
y = num;
while (y) {
++z;
y >>= 8;
}
/* handle zero */
if (z == 0) {
z = 1;
}
/* see if msb is set */
z += (num&(1UL<<((z<<3) - 1))) ? 1 : 0;
/* adjust the number so the msB is non-zero */
for (x = 0; (z <= 4) && (x < (4 - z)); x++) {
num <<= 8;
}
/* store header */
x = 0;
out[x++] = 0x02;
out[x++] = z;
/* if 31st bit is set output a leading zero and decrement count */
if (z == 5) {
out[x++] = 0;
--z;
}
/* store values */
for (y = 0; y < z; y++) {
out[x++] = (num >> 24) & 0xFF;
num <<= 8;
}
/* we good */
*outlen = x;
return CRYPT_OK;
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/short_integer/der_encode_short_integer.c,v $ */
/* $Revision: 1.3 $ */
/* $Date: 2005/05/23 01:27:03 $ */
|
