src/auths/b64decode.c

   1 /*************************************************
   2 *     Exim - an Internet mail transport agent    *
   3 *************************************************/
   4
   5 /* Copyright (c) University of Cambridge 1995 - 2009 */
   6 /* See the file NOTICE for conditions of use and distribution. */
   7
   8 #include "../exim.h"
   9
  10
  11 /*************************************************
  12 *          Decode byte-string in base 64         *
  13 *************************************************/
  14
  15 /* This function decodes a string in base 64 format as defined in RFC 2045
  16 (MIME) and required by the SMTP AUTH extension (RFC 2554). The decoding
  17 algorithm is written out in a straightforward way. Turning it into some kind of
  18 compact loop is messy and would probably run more slowly.
  19
  20 Arguments:
  21   code        points to the coded string, zero-terminated
  22   ptr         where to put the pointer to the result, which is in
  23               dynamic store, and zero-terminated
  24
  25 Returns:      the number of bytes in the result,
  26               or -1 if the input was malformed
  27
  28 A zero is added on to the end to make it easy in cases where the result is to
  29 be interpreted as text. This is not included in the count. */
  30
  31 static uschar dec64table[] = {
  32   255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, /*  0-15 */
  33   255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, /* 16-31 */
  34   255,255,255,255,255,255,255,255,255,255,255, 62,255,255,255, 63, /* 32-47 */
  35    52, 53, 54, 55, 56, 57, 58, 59, 60, 61,255,255,255,255,255,255, /* 48-63 */
  36   255,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, /* 64-79 */
  37    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,255,255,255,255,255, /* 80-95 */
  38   255, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, /* 96-111 */
  39    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51,255,255,255,255,255  /* 112-127*/
  40 };
  41
  42 int
  43 auth_b64decode(uschar *code, uschar **ptr)
  44 {
  45 register int x, y;
  46 uschar *result = store_get(3*(Ustrlen(code)/4) + 1);
  47
  48 *ptr = result;
  49
  50 /* Each cycle of the loop handles a quantum of 4 input bytes. For the last
  51 quantum this may decode to 1, 2, or 3 output bytes. */
  52
  53 while ((x = (*code++)) != 0)
  54   {
  55   if (x > 127 || (x = dec64table[x]) == 255) return -1;
  56   if ((y = (*code++)) == 0 || (y = dec64table[y]) == 255)
  57     return -1;
  58   *result++ = (x << 2) | (y >> 4);
  59
  60   if ((x = (*code++)) == '=')
  61     {
  62     if (*code++ != '=' || *code != 0) return -1;
  63     }
  64   else
  65     {
  66     if (x > 127 || (x = dec64table[x]) == 255) return -1;
  67     *result++ = (y << 4) | (x >> 2);
  68     if ((y = (*code++)) == '=')
  69       {
  70       if (*code != 0) return -1;
  71       }
  72     else
  73       {
  74       if (y > 127 || (y = dec64table[y]) == 255) return -1;
  75       *result++ = (x << 6) | y;
  76       }
  77     }
  78   }
  79
  80 *result = 0;
  81 return result - *ptr;
  82 }
  83
  84 /* End of b64decode.c */