base64_encode.c

常用的64位密码加密算法

/* 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
 */
/* compliant base64 code donated by Wayne Scott ([e-mail]) */
#include "mycrypt.h"

#ifdef BASE64

static const char *codes = 
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

int base64_encode(const unsigned char *in,  unsigned long len, 
                        unsigned char *out, unsigned long *outlen)
{
   unsigned long i, len2, leven;
   unsigned char *p;

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

   /* valid output size ? */
   len2 = 4 * ((len + 2) / 3);
   if (*outlen < len2 + 1) {
      return CRYPT_BUFFER_OVERFLOW;
   }
   p = out;
   leven = 3*(len / 3);
   for (i = 0; i < leven; i += 3) {
       *p++ = codes[(in[0] >> 2) & 0x3F];
       *p++ = codes[(((in[0] & 3) << 4) + (in[1] >> 4)) & 0x3F];
       *p++ = codes[(((in[1] & 0xf) << 2) + (in[2] >> 6)) & 0x3F];
       *p++ = codes[in[2] & 0x3F];
       in += 3;
   }
   /* Pad it if necessary...  */
   if (i < len) {
       unsigned a = in[0];
       unsigned b = (i+1 < len) ? in[1] : 0;

       *p++ = codes[(a >> 2) & 0x3F];
       *p++ = codes[(((a & 3) << 4) + (b >> 4)) & 0x3F];
       *p++ = (i+1 < len) ? codes[(((b & 0xf) << 2)) & 0x3F] : '=';
       *p++ = '=';
   }

   /* append a NULL byte */
   *p = '\0';

   /* return ok */
   *outlen = p - out;
   return CRYPT_OK;
}

#endif