xref: /src/lib/libc/net/base64.c

/*	$NetBSD: base64.c,v 1.17 2024/01/20 14:52:48 christos Exp $	*/

/*
 * Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
 * Copyright (c) 1996-1999 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 ISC DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS.  IN NO EVENT SHALL ISC 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 <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
#if 0
static const char rcsid[] = "Id: base64.c,v 1.4 2005/04/27 04:56:34 sra Exp";
#else
__RCSID("$NetBSD: base64.c,v 1.17 2024/01/20 14:52:48 christos Exp $");
#endif
#endif /* LIBC_SCCS and not lint */

#include "port_before.h"

#include <sys/types.h>
#include <sys/param.h>
#include <sys/socket.h>

#include <netinet/in.h>
#include <arpa/inet.h>
#include <arpa/nameser.h>

#include <assert.h>
#include <ctype.h>
#include <resolv.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "port_after.h"

#define Assert(Cond) if (!(Cond)) abort()

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 RFC1521 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(u_char const *src, size_t srclength, char *target, size_t targsize) {
	size_t datalength = 0;
	u_char input[3];
	u_char output[4];
	size_t i;

	_DIAGASSERT(src != NULL);
	_DIAGASSERT(target != NULL);

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

		output[0] = (uint32_t)input[0] >> 2;
		output[1] = ((uint32_t)(input[0] & 0x03) << 4) +
		    ((uint32_t)input[1] >> 4);
		output[2] = ((uint32_t)(input[1] & 0x0f) << 2) +
		    ((uint32_t)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 (0U != srclength) {
		/* Get what's left. */
		input[0] = input[1] = input[2] = '\0';
		for (i = 0; i < srclength; i++)
			input[i] = *src++;

		output[0] = (uint32_t)input[0] >> 2;
		output[1] = ((uint32_t)(input[0] & 0x03) << 4) +
		    ((uint32_t)input[1] >> 4);
		output[2] = ((uint32_t)(input[1] & 0x0f) << 2) +
		    ((uint32_t)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 == 1U)
			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. */
	_DIAGASSERT(__type_fit(int, datalength));
	return (int)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(char const *src, u_char *target, size_t targsize)
{
	size_t tarindex;
	int state, ch;
	u_char nextbyte;
	const char *pos;

	_DIAGASSERT(src != NULL);
	_DIAGASSERT(target != NULL);

	state = 0;
	tarindex = 0;

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

		if (ch == Pad64)
			break;

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

		switch (state) {
		case 0:
			if (target) {
				if (tarindex >= targsize)
					return -1;
				target[tarindex] = (u_char)(pos - Base64) << 2;
			}
			state = 1;
			break;
		case 1:
			if (target) {
				if (tarindex >= targsize)
					return -1;
				target[tarindex] |=
				    (uint32_t)(pos - Base64) >> 4;
				nextbyte = (u_char)((pos - Base64) & 0x0f) << 4;
				if (tarindex + 1 < targsize)
					target[tarindex + 1] = nextbyte;
				else if (nextbyte)
					return -1;
			}
			tarindex++;
			state = 2;
			break;
		case 2:
			if (target) {
				if (tarindex >= targsize)
					return -1;
				target[tarindex] |=
					(uint32_t)(pos - Base64) >> 2;
				nextbyte = (u_char)((pos - Base64) & 0x03) << 6;
				if (tarindex + 1 < targsize)
					target[tarindex + 1] = nextbyte;
				else if (nextbyte)
					return -1;
			}
			tarindex++;
			state = 3;
			break;
		case 3:
			if (target) {
				if ((size_t)tarindex >= targsize)
					return -1;
				target[tarindex] |= (u_char)(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 (; ch != '\0'; ch = (u_char) *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 (; ch != '\0'; ch = (u_char) *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 && tarindex < targsize &&
			    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;
	}

	_DIAGASSERT(__type_fit(int, tarindex));
	return (int)tarindex;
}

/*! \file */