text: /* OPENBSD ORIGINAL: lib/libc/net/base64.c */
  
  /*	$OpenBSD: base64.c,v 1.4 2002/01/02 23:00:10 deraadt Exp $	*/
  
  /*
   * Copyright (c) 1996 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 "base64.h"
  
  static const char Base64[] =
  	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
  static const char Pad64 = '=';
  
  inline bool isspace( int c )
  {
  	return ( ( ( c >= 0x09 ) && ( c <= 0x0D ) ) || ( c == 0x20 ) );
  }
  
  
  /* (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( unsigned char const *src, long srclength, char *target, long targsize)
  {
  	long datalength = 0;
  	unsigned char input[3];
  	unsigned char output[4];
  	long 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( char const *src, unsigned char *target, long targsize)
  {
  	int tarindex, state, ch;
  	const 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 (tarindex >= targsize)
  					return (-1);
  				target[tarindex] = (unsigned char)(pos - Base64) << 2;
  			}
  			state = 1;
  			break;
  		case 1:
  			if (target) {
  				if (tarindex + 1 >= targsize)
  					return (-1);
  				target[tarindex]   |=  (pos - Base64) >> 4;
  				target[tarindex+1]  = (unsigned char)((pos - Base64) & 0x0f) << 4 ;
  			}
  			tarindex++;
  			state = 2;
  			break;
  		case 2:
  			if (target) {
  				if (tarindex + 1 >= targsize)
  					return (-1);
  				target[tarindex]   |=  (pos - Base64) >> 2;
  				target[tarindex+1]  = (unsigned char)((pos - Base64) & 0x03) << 6;
  			}
  			tarindex++;
  			state = 3;
  			break;
  		case 3:
  			if (target) {
  				if (tarindex >= targsize)
  					return (-1);
  				target[tarindex] |= (pos - Base64);
  			}
  			tarindex++;
  			state = 0;
  			break;
  		}
  	}
  
  	/*
  	 * 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 = *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 = *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);
  }
  