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_decode_bit_string.c
15  ASN.1 DER, encode a BIT STRING, Tom St Denis
16*/
17
18
19#ifdef LTC_DER
20
21/**
22  Store a BIT STRING
23  @param in      The DER encoded BIT STRING
24  @param inlen   The size of the DER BIT STRING
25  @param out     [out] The array of bits stored (one per char)
26  @param outlen  [in/out] The number of bits stored
27  @return CRYPT_OK if successful
28*/
29int der_decode_bit_string(const unsigned char *in,  unsigned long inlen,
30                                unsigned char *out, unsigned long *outlen)
31{
32   unsigned long dlen, blen, x, y;
33
34   LTC_ARGCHK(in     != NULL);
35   LTC_ARGCHK(out    != NULL);
36   LTC_ARGCHK(outlen != NULL);
37
38   /* packet must be at least 4 bytes */
39   if (inlen < 4) {
40       return CRYPT_INVALID_ARG;
41   }
42
43   /* check for 0x03 */
44   if ((in[0]&0x1F) != 0x03) {
45      return CRYPT_INVALID_PACKET;
46   }
47
48    /* offset in the data */
49    x = 1;
50
51   /* get the length of the data */
52   if (in[x] & 0x80) {
53      /* long format get number of length bytes */
54      y = in[x++] & 0x7F;
55
56      /* invalid if 0 or > 2 */
57      if (y == 0 || y > 2) {
58         return CRYPT_INVALID_PACKET;
59      }
60
61      /* read the data len */
62      dlen = 0;
63      while (y--) {
64         dlen = (dlen << 8) | (unsigned long)in[x++];
65      }
66   } else {
67      /* short format */
68      dlen = in[x++] & 0x7F;
69   }
70
71   /* is the data len too long or too short? */
72   if ((dlen == 0) || (dlen + x > inlen)) {
73       return CRYPT_INVALID_PACKET;
74   }
75
76   /* get padding count */
77   blen = ((dlen - 1) << 3) - (in[x++] & 7);
78
79   /* too many bits? */
80   if (blen > *outlen) {
81      *outlen = blen;
82      return CRYPT_BUFFER_OVERFLOW;
83   }
84
85   /* decode/store the bits */
86   for (y = 0; y < blen; y++) {
87       out[y] = (in[x] & (1 << (7 - (y & 7)))) ? 1 : 0;
88       if ((y & 7) == 7) {
89          ++x;
90       }
91   }
92
93   /* we done */
94   *outlen = blen;
95   return CRYPT_OK;
96}
97
98#endif
99
100/* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/bit/der_decode_bit_string.c,v $ */
101/* $Revision: 1.4 $ */
102/* $Date: 2006/06/16 21:53:41 $ */
103