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