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Diffstat (limited to 'lib/rc4.c')
| -rw-r--r-- | lib/rc4.c | 189 |
1 files changed, 189 insertions, 0 deletions
diff --git a/lib/rc4.c b/lib/rc4.c new file mode 100644 index 00000000..5e334507 --- /dev/null +++ b/lib/rc4.c @@ -0,0 +1,189 @@ +/***************************************************************************\ +* * +* BitlBee - An IRC to IM gateway * +* Simple (but secure) RC4 implementation for safer password storage. * +* * +* Copyright 2006 Wilmer van der Gaast <wilmer@gaast.net> * +* * +* This program is free software; you can redistribute it and/or modify * +* it under the terms of the GNU General Public License as published by * +* the Free Software Foundation; either version 2 of the License, or * +* (at your option) any later version. * +* * +* This program 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 General Public License for more details. * +* * +* You should have received a copy of the GNU General Public License along * +* with this program; if not, write to the Free Software Foundation, Inc., * +* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. * +* * +\***************************************************************************/ + +/* + This file implements RC4-encryption, which will mainly be used to save IM + passwords safely in the new XML-format. Possibly other uses will come up + later. It's supposed to be quite reliable (thanks to the use of a 6-byte + IV/seed), certainly compared to the old format. The only realistic way to + crack BitlBee passwords now is to use a sniffer to get your hands on the + user's password. + + If you see that something's wrong in this implementation (I asked a + couple of people to look at it already, but who knows), please tell me. + + The reason I chose for RC4 is because it's pretty simple but effective, + so it will work without adding several KBs or an extra library dependency. +*/ + + +#include <glib.h> +#include <gmodule.h> +#include <stdlib.h> +#include <string.h> +#include "misc.h" +#include "rc4.h" + +/* Add some seed to the password, to make sure we *never* use the same key. + This defines how many byes we use as a seed. */ +#define RC4_IV_LEN 6 + +/* To defend against a "Fluhrer, Mantin and Shamir attack", it is recommended + to shuffle S[] just a bit more before you start to use it. This defines how + many bytes we'll request before we'll really use them for encryption. */ +#define RC4_CYCLES 1024 + +struct rc4_state *rc4_keymaker( unsigned char *key, int kl, int cycles ) +{ + struct rc4_state *st; + int i, j, tmp; + + st = g_malloc( sizeof( struct rc4_state ) ); + st->i = st->j = 0; + for( i = 0; i < 256; i ++ ) + st->S[i] = i; + + if( kl <= 0 ) + kl = strlen( (char*) key ); + + for( i = j = 0; i < 256; i ++ ) + { + j = ( j + st->S[i] + key[i%kl] ) & 0xff; + tmp = st->S[i]; + st->S[i] = st->S[j]; + st->S[j] = tmp; + } + + for( i = 0; i < cycles; i ++ ) + rc4_getbyte( st ); + + return st; +} + +/* + For those who don't know, RC4 is basically an algorithm that generates a + stream of bytes after you give it a key. Just get a byte from it and xor + it with your cleartext. To decrypt, just give it the same key again and + start xorring. + + The function above initializes the RC4 byte generator, the next function + can be used to get bytes from the generator (and shuffle things a bit). +*/ + +unsigned char rc4_getbyte( struct rc4_state *st ) +{ + unsigned char tmp; + + /* Unfortunately the st-> stuff doesn't really improve readability here... */ + st->i ++; + st->j += st->S[st->i]; + tmp = st->S[st->i]; + st->S[st->i] = st->S[st->j]; + st->S[st->j] = tmp; + + return st->S[(st->S[st->i] + st->S[st->j]) & 0xff]; +} + +/* + The following two functions can be used for reliable encryption and + decryption. Known plaintext attacks are prevented by adding some (6, + by default) random bytes to the password before setting up the RC4 + structures. These 6 bytes are also saved in the results, because of + course we'll need them in rc4_decode(). + + Because the length of the resulting string is unknown to the caller, + it should pass a char**. Since the encode/decode functions allocate + memory for the string, make sure the char** points at a NULL-pointer + (or at least to something you already free()d), or you'll leak + memory. And of course, don't forget to free() the result when you + don't need it anymore. + + Both functions return the number of bytes in the result string. +*/ + +int rc4_encode( unsigned char *clear, int clear_len, unsigned char **crypt, char *password ) +{ + struct rc4_state *st; + unsigned char *key; + int key_len, i; + + key_len = strlen( password ) + RC4_IV_LEN; + if( clear_len <= 0 ) + clear_len = strlen( (char*) clear ); + + /* Prepare buffers and the key + IV */ + *crypt = g_malloc( clear_len + RC4_IV_LEN ); + key = g_malloc( key_len ); + strcpy( (char*) key, password ); + + /* Add the salt. Save it for later (when decrypting) and, of course, + add it to the encryption key. */ + random_bytes( crypt[0], RC4_IV_LEN ); + memcpy( key + key_len - RC4_IV_LEN, crypt[0], RC4_IV_LEN ); + + /* Generate the initial S[] from the IVed key. */ + st = rc4_keymaker( key, key_len, RC4_CYCLES ); + g_free( key ); + + for( i = 0; i < clear_len; i ++ ) + crypt[0][i+RC4_IV_LEN] = clear[i] ^ rc4_getbyte( st ); + + g_free( st ); + + return clear_len + RC4_IV_LEN; +} + +int rc4_decode( unsigned char *crypt, int crypt_len, unsigned char **clear, char *password ) +{ + struct rc4_state *st; + unsigned char *key; + int key_len, clear_len, i; + + key_len = strlen( password ) + RC4_IV_LEN; + clear_len = crypt_len - RC4_IV_LEN; + + if( clear_len < 0 ) + { + *clear = (unsigned char*) g_strdup( "" ); + return 0; + } + + /* Prepare buffers and the key + IV */ + *clear = g_malloc( clear_len + 1 ); + key = g_malloc( key_len ); + strcpy( (char*) key, password ); + for( i = 0; i < RC4_IV_LEN; i ++ ) + key[key_len-RC4_IV_LEN+i] = crypt[i]; + + /* Generate the initial S[] from the IVed key. */ + st = rc4_keymaker( key, key_len, RC4_CYCLES ); + g_free( key ); + + for( i = 0; i < clear_len; i ++ ) + clear[0][i] = crypt[i+RC4_IV_LEN] ^ rc4_getbyte( st ); + clear[0][i] = 0; /* Nice to have for plaintexts. */ + + g_free( st ); + + return clear_len; +} |