/*
 * Copyright (c) 1996, 1998 by Internet Software Consortium.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
 * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
 * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
 * SOFTWARE.
 */

/*
 * 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 <ctype.h>
#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>

#define Assert(Cond) ((void) 0)

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.
   */

/* 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.
 */

static int b64rmap_initialized = 0;
static uint8_t b64rmap[256];

static const uint8_t b64rmap_special = 0xf0;
static const uint8_t b64rmap_end = 0xfd;
static const uint8_t b64rmap_space = 0xfe;
static const uint8_t b64rmap_invalid = 0xff;

/**
 * Initializing the reverse map is not thread safe.
 * Which is fine for NSD. For now...
 **/
static void
b64_initialize_rmap (void)
{
	int i;

	/* Null: end of string, stop parsing */
	b64rmap[0] = b64rmap_end;

	for (i = 1; i < 256; ++i) {
		/* Whitespaces */
		if (isspace(i))
			b64rmap[i] = b64rmap_space;
		/* Padding: stop parsing */
		else if (i == (unsigned char)Pad64)
			b64rmap[i] = b64rmap_end;
		/* Non-base64 char */
		else
			b64rmap[i] = b64rmap_invalid;
	}

	/* Fill reverse mapping for base64 chars */
	for (i = 0; Base64[i] != '\0'; ++i)
		b64rmap[(uint8_t)Base64[i]] = i;

	b64rmap_initialized = 1;
}

static int
b64_decode_do(unsigned char const *src, uint8_t *target, size_t targsize)
{
	int tarindex, state, ch;
	uint8_t ofs;

	state = 0;
	tarindex = 0;

	while (1)
	{
		ch = *src++;
		ofs = b64rmap[ch];

		if (ofs >= b64rmap_special) {
			/* Ignore whitespaces */
			if (ofs == b64rmap_space)
				continue;
			/* End of base64 characters */
			if (ofs == b64rmap_end)
				break;
			/* A non-base64 character. */
			return (-1);
		}

		switch (state) {
		case 0:
			if ((size_t)tarindex >= targsize)
				return (-1);
			target[tarindex] = ofs << 2;
			state = 1;
			break;
		case 1:
			if ((size_t)tarindex + 1 >= targsize)
				return (-1);
			target[tarindex]   |=  ofs >> 4;
			target[tarindex+1]  = (ofs & 0x0f)
						<< 4 ;
			tarindex++;
			state = 2;
			break;
		case 2:
			if ((size_t)tarindex + 1 >= targsize)
				return (-1);
			target[tarindex]   |=  ofs >> 2;
			target[tarindex+1]  = (ofs & 0x03)
						<< 6;
			tarindex++;
			state = 3;
			break;
		case 3:
			if ((size_t)tarindex >= targsize)
				return (-1);
			target[tarindex] |= ofs;
			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 ((void)NULL; ch != '\0'; ch = *src++)
				if (b64rmap[ch] != b64rmap_space)
					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 ((void)NULL; ch != '\0'; ch = *src++)
				if (b64rmap[ch] != b64rmap_space)
					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[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);
}


static int
b64_decode_len(unsigned char const *src)
{
	int tarindex, state, ch;
	uint8_t ofs;

	state = 0;
	tarindex = 0;

	while (1)
	{
		ch = *src++;
		ofs = b64rmap[ch];

		if (ofs >= b64rmap_special) {
			/* Ignore whitespaces */
			if (ofs == b64rmap_space)
				continue;
			/* End of base64 characters */
			if (ofs == b64rmap_end)
				break;
			/* A non-base64 character. */
			return (-1);
		}

		switch (state) {
		case 0:
			state = 1;
			break;
		case 1:
			tarindex++;
			state = 2;
			break;
		case 2:
			tarindex++;
			state = 3;
			break;
		case 3:
			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 ((void)NULL; ch != '\0'; ch = *src++)
				if (b64rmap[ch] != b64rmap_space)
					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 ((void)NULL; ch != '\0'; ch = *src++)
				if (b64rmap[ch] != b64rmap_space)
					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);
}


int
b64_decode(char const *src, uint8_t *target, size_t targsize)
{
	if (!b64rmap_initialized)
		b64_initialize_rmap ();

	if (target)
		return b64_decode_do ((unsigned char*)src, target, targsize);
	else
		return b64_decode_len ((unsigned char*)src);
}
