/*
 * Portions Copyright (c) 1995 by International Business Machines, Inc.
 *
 * International Business Machines, Inc. (hereinafter called IBM) grants
 * permission under its copyrights to use, copy, modify, and distribute this
 * Software with or without fee, provided that the above copyright notice and
 * all paragraphs of this notice appear in all copies, and that the name of IBM
 * not be used in connection with the marketing of any product incorporating
 * the Software or modifications thereof, without specific, written prior
 * permission.
 *
 * To the extent it has a right to do so, IBM grants an immunity from suit
 * under its patents, if any, for the use, sale or manufacture of products to
 * the extent that such products are used for performing Domain Name System
 * dynamic updates in TCP/IP networks by means of the Software.  No immunity is
 * granted for any product per se or for any other function of any product.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", AND IBM DISCLAIMS ALL WARRANTIES,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE.  IN NO EVENT SHALL IBM BE LIABLE FOR ANY SPECIAL,
 * DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE, EVEN
 * IF IBM IS APPRISED OF THE POSSIBILITY OF SUCH DAMAGES.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define Assert(Cond) if (!(Cond)) return(-1);

static const char Base64[] =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
static const char Pad64 = '=';

/* (From RFC1521 and draft-ietf-dnssec-secext-03.txt)
   The following encoding technique is taken from RFC 1521 by Borenstein
   and Freed.  It is reproduced here in a slightly edited form for
   convenience.

   A 65-character subset of US-ASCII is used, enabling 6 bits to be
   represented per printable character. (The extra 65th character, "=",
   is used to signify a special processing function.)

   The encoding process represents 24-bit groups of input bits as output
   strings of 4 encoded characters. Proceeding from left to right, a
   24-bit input group is formed by concatenating 3 8-bit input groups.
   These 24 bits are then treated as 4 concatenated 6-bit groups, each
   of which is translated into a single digit in the base64 alphabet.

   Each 6-bit group is used as an index into an array of 64 printable
   characters. The character referenced by the index is placed in the
   output string.

                         Table 1: The Base64 Alphabet

      Value Encoding  Value Encoding  Value Encoding  Value Encoding
          0 A            17 R            34 i            51 z
          1 B            18 S            35 j            52 0
          2 C            19 T            36 k            53 1
          3 D            20 U            37 l            54 2
          4 E            21 V            38 m            55 3
          5 F            22 W            39 n            56 4
          6 G            23 X            40 o            57 5
          7 H            24 Y            41 p            58 6
          8 I            25 Z            42 q            59 7
          9 J            26 a            43 r            60 8
         10 K            27 b            44 s            61 9
         11 L            28 c            45 t            62 +
         12 M            29 d            46 u            63 /
         13 N            30 e            47 v
         14 O            31 f            48 w         (pad) =
         15 P            32 g            49 x
         16 Q            33 h            50 y

   Special processing is performed if fewer than 24 bits are available
   at the end of the data being encoded.  A full encoding quantum is
   always completed at the end of a quantity.  When fewer than 24 input
   bits are available in an input group, zero bits are added (on the
   right) to form an integral number of 6-bit groups.  Padding at the
   end of the data is performed using the '=' character.

   Since all base64 input is an integral number of octets, only the
         -------------------------------------------------
   following cases can arise:

       (1) the final quantum of encoding input is an integral
           multiple of 24 bits; here, the final unit of encoded
           output will be an integral multiple of 4 characters
           with no "=" padding,
       (2) the final quantum of encoding input is exactly 8 bits;
           here, the final unit of encoded output will be two
           characters followed by two "=" padding characters, or
       (3) the final quantum of encoding input is exactly 16 bits;
           here, the final unit of encoded output will be three
           characters followed by one "=" padding character.
   */

int
b64_ntop(src, srclength, target, targsize)
        unsigned char const *src;
        size_t srclength;
        char *target;
        size_t targsize;
{
        size_t datalength = 0;
        unsigned char input[3];
        unsigned char output[4];
        size_t i;

        while (2 < srclength) {
                input[0] = *src++;
                input[1] = *src++;
                input[2] = *src++;
                srclength -= 3;

                output[0] = input[0] >> 2;
                output[1] = ((input[0] & 0x03) << 4) + (input[1] >> 4);
                output[2] = ((input[1] & 0x0f) << 2) + (input[2] >> 6);
                output[3] = input[2] & 0x3f;
                Assert(output[0] < 64);
                Assert(output[1] < 64);
                Assert(output[2] < 64);
                Assert(output[3] < 64);

                if (datalength + 4 > targsize)
                        return (-1);
                target[datalength++] = Base64[output[0]];
                target[datalength++] = Base64[output[1]];
                target[datalength++] = Base64[output[2]];
                target[datalength++] = Base64[output[3]];
        }

        /* Now we worry about padding. */
        if (0 != srclength) {
                /* Get what's left. */
                input[0] = input[1] = input[2] = '\0';
                for (i = 0; i < srclength; i++)
                        input[i] = *src++;

                output[0] = input[0] >> 2;
                output[1] = ((input[0] & 0x03) << 4) + (input[1] >> 4);
                output[2] = ((input[1] & 0x0f) << 2) + (input[2] >> 6);
                Assert(output[0] < 64);
                Assert(output[1] < 64);
                Assert(output[2] < 64);

                if (datalength + 4 > targsize)
                        return (-1);
                target[datalength++] = Base64[output[0]];
                target[datalength++] = Base64[output[1]];
                if (srclength == 1)
                        target[datalength++] = Pad64;
                else
                        target[datalength++] = Base64[output[2]];
                target[datalength++] = Pad64;
        }
        if (datalength >= targsize)
                return (-1);
        target[datalength] = '\0';      /* Returned value doesn't count \0. */
        return (datalength);
}

/* skips all whitespace anywhere.
   converts characters, four at a time, starting at (or after)
   src from base - 64 numbers into three 8 bit bytes in the target area.
   it returns the number of data bytes stored at the target, or -1 on error.
 */

int
b64_pton(src, target, targsize)
        char const *src;
        unsigned char *target;
        size_t targsize;
{
        int tarindex, state, ch;
        char *pos;

        state = 0;
        tarindex = 0;

        while ((ch = *src++) != '\0') {
                if (isspace(ch))        /* Skip whitespace anywhere. */
                        continue;

                if (ch == Pad64)
                        break;

                pos = strchr(Base64, ch);
                if (pos == 0)           /* A non-base64 character. */
                        return (-1);

                switch (state) {
                case 0:
                        if (target) {
                                if ((size_t)tarindex >= targsize)
                                        return (-1);
                                target[tarindex] = (pos - Base64) << 2;
                        }
                        state = 1;
                        break;
                case 1:
                        if (target) {
                                if ((size_t)(tarindex + 1) >= targsize)
                                        return (-1);
                                target[tarindex]   |=  (pos - Base64) >> 4;
                                target[tarindex+1]  = ((pos - Base64) & 0x0f)
                                                        << 4 ;
                        }
                        tarindex++;
                        state = 2;
                        break;
                case 2:
                        if (target) {
                                if ((size_t)(tarindex + 1) >= targsize)
                                        return (-1);
                                target[tarindex]   |=  (pos - Base64) >> 2;
                                target[tarindex+1]  = ((pos - Base64) & 0x03)
                                                        << 6;
                        }
                        tarindex++;
                        state = 3;
                        break;
                case 3:
                        if (target) {
                                if ((size_t)tarindex >= targsize)
                                        return (-1);
                                target[tarindex] |= (pos - Base64);
                        }
                        tarindex++;
                        state = 0;
                        break;
                default:
                        abort();
                }
        }

        /*
         * We are done decoding Base-64 chars.  Let's see if we ended
         * on a byte boundary, and/or with erroneous trailing characters.
         */

        if (ch == Pad64) {              /* We got a pad char. */
                ch = *src++;            /* Skip it, get next. */
                switch (state) {
                case 0:         /* Invalid = in first position */
                case 1:         /* Invalid = in second position */
                        return (-1);

                case 2:         /* Valid, means one byte of info */
                        /* Skip any number of spaces. */
                        for (NULL; ch != '\0'; ch = *src++)
                                if (!isspace(ch))
                                        break;
                        /* Make sure there is another trailing = sign. */
                        if (ch != Pad64)
                                return (-1);
                        ch = *src++;            /* Skip the = */
                        /* Fall through to "single trailing =" case. */
                        /* FALLTHROUGH */

                case 3:         /* Valid, means two bytes of info */
                        /*
                         * We know this char is an =.  Is there anything but
                         * whitespace after it?
                         */
                        for (NULL; ch != '\0'; ch = *src++)
                                if (!isspace(ch))
                                        return (-1);

                        /*
                         * Now make sure for cases 2 and 3 that the "extra"
                         * bits that slopped past the last full byte were
                         * zeros.  If we don't check them, they become a
                         * subliminal channel.
                         */
                        if (target && target[tarindex] != 0)
                                return (-1);
                }
        } else {
                /*
                 * We ended by seeing the end of the string.  Make sure we
                 * have no partial bytes lying around.
                 */
                if (state != 0)
                        return (-1);
        }

        return (tarindex);
}
