der_decode_object_identifier.c

这是由Rinick编写的加解密函数库。最近找了不少关于加解密的C源码

/* 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, [e-mail], http://libtomcrypt.org
 */
#include "tomcrypt.h"

/**
  @file der_decode_object_identifier.c
  ASN.1 DER, Decode Object Identifier, Tom St Denis
*/

#ifdef LTC_DER
/**
  Decode OID data and store the array of integers in words
  @param in      The OID DER encoded data
  @param inlen   The length of the OID data
  @param words   [out] The destination of the OID words
  @param outlen  [in/out] The number of OID words
  @return CRYPT_OK if successful
*/
int der_decode_object_identifier(const unsigned char *in,    unsigned long  inlen,
                                       unsigned long *words, unsigned long *outlen)
{
   unsigned long x, y, t, len;

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

   /* header is at least 3 bytes */
   if (inlen < 3) {
      return CRYPT_INVALID_PACKET;
   }

   /* must be room for at least two words */
   if (*outlen < 2) {
      return CRYPT_BUFFER_OVERFLOW;
   }

   /* decode the packet header */
   x = 0;
   if ((in[x++] & 0x1F) != 0x06) {
      return CRYPT_INVALID_PACKET;
   }
   
   /* get the length */
   if (in[x] < 128) {
      len = in[x++]; 
   } else {
       if (in[x] < 0x81 || in[x] > 0x82) {
          return CRYPT_INVALID_PACKET;
       }
       y   = in[x++] & 0x7F;
       len = 0;
       while (y--) {
          len = (len << 8) | (unsigned long)in[x++];
       }
   }

   if (len < 1 || (len + x) > inlen) {
      return CRYPT_INVALID_PACKET;
   }

   /* decode word1 and word2 */
   --len;
   t = in[x++];
   words[0] = t/40;
   words[1] = t%40;

   /* decode rest */
   y = 2;
   t = 0;
   while (len--) {
       t = (t << 7) | (in[x] & 0x7F);
       if (!(in[x++] & 0x80)) {
           /* store t */
           if (y >= *outlen) {
              return CRYPT_BUFFER_OVERFLOW;
           }
           words[y++] = t;
           t          = 0;
       }
   }
       
   *outlen = y;
   return CRYPT_OK;
}

#endif

/* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/object_identifier/der_decode_object_identifier.c,v $ */
/* $Revision: 1.1 $ */
/* $Date: 2005/05/16 15:08:11 $ */