libpurple/protocols/yahoo/yahoo_crypt.c

/* One way encryption based on MD5 sum.
   Copyright (C) 1996, 1997, 1999, 2000 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

/* warmenhoven took this file and made it work with the md5.[ch] we
 * already had. isn't that lovely. people should just use linux or
 * freebsd, crypt works properly on those systems. i hate solaris */

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

#include "cipher.h"
#include "yahoo_crypt.h"

/* Define our magic string to mark salt for MD5 "encryption"
   replacement.  This is meant to be the same as for other MD5 based
   encryption implementations.  */
static const char md5_salt_prefix[] = "$1$";

/* Table with characters for base64 transformation.  */
static const char b64t[64] =
"./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

char *yahoo_crypt(const char *key, const char *salt)
{
	PurpleCipher *cipher;
	PurpleCipherContext *context1, *context2;
	guchar digest[16];
	static char *buffer = NULL;
	static int buflen = 0;
	int needed = 3 + strlen (salt) + 1 + 26 + 1;

	size_t salt_len;
	size_t key_len;
	size_t cnt;

	char *cp;

	if (buflen < needed) {
		buflen = needed;
		if ((buffer = g_realloc(buffer, buflen)) == NULL)
			return NULL;
	}

	cipher = purple_ciphers_find_cipher("md5");
	context1 = purple_cipher_context_new(cipher, NULL);
	context2 = purple_cipher_context_new(cipher, NULL);

	/* Find beginning of salt string.  The prefix should normally always
	 * be present.  Just in case it is not.
	 */
	if (strncmp (md5_salt_prefix, salt, sizeof (md5_salt_prefix) - 1) == 0)
		/* Skip salt prefix.  */
		salt += sizeof (md5_salt_prefix) - 1;

	salt_len = MIN (strcspn (salt, "$"), 8);
	key_len = strlen (key);

	/* Add the key string.  */
	purple_cipher_context_append(context1, (const guchar *)key, key_len);

	/* Because the SALT argument need not always have the salt prefix we
	 * add it separately.
	 */
	purple_cipher_context_append(context1, (const guchar *)md5_salt_prefix,
							   sizeof(md5_salt_prefix) - 1);

	/* The last part is the salt string.  This must be at most 8
	 * characters and it ends at the first `$' character (for
	 * compatibility which existing solutions).
	 */
	purple_cipher_context_append(context1, (const guchar *)salt, salt_len);

	/* Compute alternate MD5 sum with input KEY, SALT, and KEY.  The
	 * final result will be added to the first context.
	 */

	/* Add key.  */
	purple_cipher_context_append(context2, (const guchar *)key, key_len);

	/* Add salt.  */
	purple_cipher_context_append(context2, (const guchar *)salt, salt_len);

	/* Add key again.  */
	purple_cipher_context_append(context2, (const guchar *)key, key_len);

	/* Now get result of this (16 bytes) and add it to the other context.  */
	purple_cipher_context_digest(context2, sizeof(digest), digest, NULL);

	/* Add for any character in the key one byte of the alternate sum.  */
	for (cnt = key_len; cnt > 16; cnt -= 16)
		purple_cipher_context_append(context1, digest, 16);
	purple_cipher_context_append(context1, digest, cnt);

	/* For the following code we need a NUL byte.  */
	digest[0] = '\0';

	/* The original implementation now does something weird: for every 1
	 * bit in the key the first 0 is added to the buffer, for every 0
	 * bit the first character of the key.  This does not seem to be
	 * what was intended but we have to follow this to be compatible.
	 */
	for (cnt = key_len; cnt > 0; cnt >>= 1)
		purple_cipher_context_append(context1,
								   (cnt & 1) != 0 ? digest : (guchar *)key, 1);

	/* Create intermediate result.  */
	purple_cipher_context_digest(context1, sizeof(digest), digest, NULL);

	/* Now comes another weirdness.  In fear of password crackers here
	 * comes a quite long loop which just processes the output of the
	 * previous round again.  We cannot ignore this here.
	 */
	for (cnt = 0; cnt < 1000; ++cnt) {
		/* New context.  */
		purple_cipher_context_reset(context2, NULL);

		/* Add key or last result.  */
		if ((cnt & 1) != 0)
			purple_cipher_context_append(context2, (const guchar *)key, key_len);
		else
			purple_cipher_context_append(context2, digest, 16);

		/* Add salt for numbers not divisible by 3.  */
		if (cnt % 3 != 0)
			purple_cipher_context_append(context2, (const guchar *)salt, salt_len);

		/* Add key for numbers not divisible by 7.  */
		if (cnt % 7 != 0)
			purple_cipher_context_append(context2, (const guchar *)key, key_len);

		/* Add key or last result.  */
		if ((cnt & 1) != 0)
			purple_cipher_context_append(context2, digest, 16);
		else
			purple_cipher_context_append(context2, (const guchar *)key, key_len);

		/* Create intermediate result.  */
		purple_cipher_context_digest(context2, sizeof(digest), digest, NULL);
	}

	/* Now we can construct the result string.  It consists of three parts. */
	strncpy(buffer, md5_salt_prefix, MAX (0, buflen));
	cp = buffer + strlen(buffer);
	buflen -= sizeof (md5_salt_prefix);

	strncpy(cp, salt, MIN ((size_t) buflen, salt_len));
	cp = cp + strlen(cp);
	buflen -= MIN ((size_t) buflen, salt_len);

	if (buflen > 0) {
		*cp++ = '$';
		--buflen;
	}

#define b64_from_24bit(B2, B1, B0, N) \
	do { \
		unsigned int w = ((B2) << 16) | ((B1) << 8) | (B0); \
		int n = (N); \
		while (n-- > 0 && buflen > 0) { \
			*cp++ = b64t[w & 0x3f]; \
			--buflen; \
			w >>= 6; \
		}\
	} while (0)

	b64_from_24bit (digest[0], digest[6], digest[12], 4);
	b64_from_24bit (digest[1], digest[7], digest[13], 4);
	b64_from_24bit (digest[2], digest[8], digest[14], 4);
	b64_from_24bit (digest[3], digest[9], digest[15], 4);
	b64_from_24bit (digest[4], digest[10], digest[5], 4);
	b64_from_24bit (0, 0, digest[11], 2);
	if (buflen <= 0) {
		g_free(buffer);
		buffer = NULL;
	} else
		*cp = '\0';	/* Terminate the string.  */

	/* Clear the buffer for the intermediate result so that people
	 * attaching to processes or reading core dumps cannot get any
	 * information.  We do it in this way to clear correct_words[]
	 * inside the MD5 implementation as well.
	 */
	purple_cipher_context_reset(context1, NULL);
	purple_cipher_context_digest(context1, sizeof(digest), digest, NULL);
	purple_cipher_context_destroy(context1);
	purple_cipher_context_destroy(context2);

	return buffer;
}