src/src/auths/b64decode.c

   1 /* $Cambridge: exim/src/src/auths/b64decode.c,v 1.1 2004/10/07 13:10:00 ph10 Exp $ */
   2
   3 /*************************************************
   4 *     Exim - an Internet mail transport agent    *
   5 *************************************************/
   6
   7 /* Copyright (c) University of Cambridge 1995 - 2004 */
   8 /* See the file NOTICE for conditions of use and distribution. */
   9
  10 #include "../exim.h"
  11
  12
  13 /*************************************************
  14 *          Decode byte-string in base 64         *
  15 *************************************************/
  16
  17 /* This function decodes a string in base 64 format as defined in RFC 2045
  18 (MIME) and required by the SMTP AUTH extension (RFC 2554). The decoding
  19 algorithm is written out in a straightforward way. Turning it into some kind of
  20 compact loop is messy and would probably run more slowly.
  21
  22 Arguments:
  23   code        points to the coded string, zero-terminated
  24   ptr         where to put the pointer to the result, which is in
  25               dynamic store
  26
  27 Returns:      the number of bytes in the result,
  28               or -1 if the input was malformed
  29
  30 A zero is added on to the end to make it easy in cases where the result is to
  31 be interpreted as text. This is not included in the count. */
  32
  33 static uschar dec64table[] = {
  34   255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, /*  0-15 */
  35   255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, /* 16-31 */
  36   255,255,255,255,255,255,255,255,255,255,255, 62,255,255,255, 63, /* 32-47 */
  37    52, 53, 54, 55, 56, 57, 58, 59, 60, 61,255,255,255,255,255,255, /* 48-63 */
  38   255,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, /* 64-79 */
  39    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,255,255,255,255,255, /* 80-95 */
  40   255, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, /* 96-111 */
  41    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51,255,255,255,255,255  /* 112-127*/
  42 };
  43
  44 int
  45 auth_b64decode(uschar *code, uschar **ptr)
  46 {
  47 register int x, y;
  48 uschar *result = store_get(3*(Ustrlen(code)/4) + 1);
  49
  50 *ptr = result;
  51
  52 /* Each cycle of the loop handles a quantum of 4 input bytes. For the last
  53 quantum this may decode to 1, 2, or 3 output bytes. */
  54
  55 while ((x = (*code++)) != 0)
  56   {
  57   if (x > 127 || (x = dec64table[x]) == 255) return -1;
  58   if ((y = (*code++)) == 0 || (y = dec64table[y]) == 255)
  59     return -1;
  60   *result++ = (x << 2) | (y >> 4);
  61
  62   if ((x = (*code++)) == '=')
  63     {
  64     if (*code++ != '=' || *code != 0) return -1;
  65     }
  66   else
  67     {
  68     if (x > 127 || (x = dec64table[x]) == 255) return -1;
  69     *result++ = (y << 4) | (x >> 2);
  70     if ((y = (*code++)) == '=')
  71       {
  72       if (*code != 0) return -1;
  73       }
  74     else
  75       {
  76       if (y > 127 || (y = dec64table[y]) == 255) return -1;
  77       *result++ = (x << 6) | y;
  78       }
  79     }
  80   }
  81
  82 *result = 0;
  83 return result - *ptr;
  84 }
  85
  86 /* End of b64decode.c */