/* 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.
 */
#include "tomcrypt.h"

/**
  @file der_decode_bit_string.c
  ASN.1 DER, encode a BIT STRING, Tom St Denis
*/


#ifdef LTC_DER

/**
  Store a BIT STRING
  @param in      The DER encoded BIT STRING
  @param inlen   The size of the DER BIT STRING
  @param out     [out] The array of bits stored (one per char)
  @param outlen  [in/out] The number of bits stored
  @return CRYPT_OK if successful
*/
int der_decode_bit_string(const unsigned char *in,  unsigned long inlen,
                                unsigned char *out, unsigned long *outlen)
{
   unsigned long dlen, blen, x, y;
   int err;

   LTC_ARGCHK(in     != NULL);
   LTC_ARGCHK(out    != NULL);
   LTC_ARGCHK(outlen != NULL);

   /* packet must be at least 4 bytes */
   if (inlen < 4) {
       return CRYPT_INVALID_ARG;
   }

   /* check for 0x03 */
   if ((in[0]&0x1F) != 0x03) {
      return CRYPT_INVALID_PACKET;
   }

   /* offset in the data */
   x = 1;

   /* get the length of the data */
   y = inlen - 1;
   if ((err = der_decode_asn1_length(in + x, &y, &dlen)) != CRYPT_OK) {
      return err;
   }
   x += y;
   /* is the data len too long or too short? */
   if ((dlen == 0) || (dlen > (inlen - x))) {
       return CRYPT_INVALID_PACKET;
   }

   /* get padding count */
   blen = ((dlen - 1) << 3) - (in[x++] & 7);

   /* too many bits? */
   if (blen > *outlen) {
      *outlen = blen;
      return CRYPT_BUFFER_OVERFLOW;
   }

   /* decode/store the bits */
   for (y = 0; y < blen; y++) {
       out[y] = (in[x] & (1 << (7 - (y & 7)))) ? 1 : 0;
       if ((y & 7) == 7) {
          ++x;
       }
   }

   /* we done */
   *outlen = blen;
   return CRYPT_OK;
}

#endif

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