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_encode_short_integer.c
15  ASN.1 DER, encode an integer, Tom St Denis
16*/
17
18
19#ifdef LTC_DER
20
21/**
22  Store a short integer in the range (0,2^32-1)
23  @param num      The integer to encode
24  @param out      [out] The destination for the DER encoded integers
25  @param outlen   [in/out] The max size and resulting size of the DER encoded integers
26  @return CRYPT_OK if successful
27*/
28int der_encode_short_integer(unsigned long num, unsigned char *out, unsigned long *outlen)
29{
30   unsigned long len, x, y, z;
31   int           err;
32
33   LTC_ARGCHK(out    != NULL);
34   LTC_ARGCHK(outlen != NULL);
35
36   /* force to 32 bits */
37   num &= 0xFFFFFFFFUL;
38
39   /* find out how big this will be */
40   if ((err = der_length_short_integer(num, &len)) != CRYPT_OK) {
41      return err;
42   }
43
44   if (*outlen < len) {
45      *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++] = (unsigned char)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++] = (unsigned char)((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: 1.7 $ */
97/* $Date: 2006/12/04 21:34:03 $ */
98