From 05d3be1048bcaec5fd989b237a8209b8aae8f6db Mon Sep 17 00:00:00 2001 From: Joshua Oreman Date: Wed, 24 Jun 2009 00:33:50 -0700 Subject: [cipher] Add the ARC4 stream cipher Signed-off-by: Marty Connor --- src/crypto/arc4.c | 131 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 131 insertions(+) create mode 100644 src/crypto/arc4.c (limited to 'src/crypto') diff --git a/src/crypto/arc4.c b/src/crypto/arc4.c new file mode 100644 index 00000000..e58fba7c --- /dev/null +++ b/src/crypto/arc4.c @@ -0,0 +1,131 @@ +/* + * The ARC4 stream cipher. + * + * Copyright (c) 2009 Joshua Oreman . + * + * 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 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., 675 Mass Ave, Cambridge, MA 02139, USA. + */ + +FILE_LICENCE ( GPL2_OR_LATER ); + +#include +#include + +#define SWAP( ary, i, j ) \ + ({ u8 temp = ary[i]; ary[i] = ary[j]; ary[j] = temp; }) + +/** + * Set ARC4 key + * + * @v ctxv ARC4 encryption context + * @v keyv Key to set + * @v keylen Length of key + * + * If an initialisation vector is to be used, it should be prepended + * to the key; ARC4 does not implement the @c setiv function because + * there is no standard length for an initialisation vector in the + * cipher. + */ +static int arc4_setkey ( void *ctxv, const void *keyv, size_t keylen ) +{ + struct arc4_ctx *ctx = ctxv; + const u8 *key = keyv; + u8 *S = ctx->state; + int i, j; + + for ( i = 0; i < 256; i++ ) { + S[i] = i; + } + + for ( i = j = 0; i < 256; i++ ) { + j = ( j + S[i] + key[i % keylen] ) & 0xff; + SWAP ( S, i, j ); + } + + ctx->i = ctx->j = 0; + return 0; +} + +/** + * Perform ARC4 encryption or decryption + * + * @v ctxv ARC4 encryption context + * @v srcv Data to encrypt or decrypt + * @v dstv Location to store encrypted or decrypted data + * @v len Length of data to operate on + * + * ARC4 is a stream cipher that works by generating a stream of PRNG + * data based on the key, and XOR'ing it with the data to be + * encrypted. Since XOR is symmetric, encryption and decryption in + * ARC4 are the same operation. + * + * If you pass a @c NULL source or destination pointer, @a len + * keystream bytes will be consumed without encrypting any data. + */ +static void arc4_xor ( void *ctxv, const void *srcv, void *dstv, + size_t len ) +{ + struct arc4_ctx *ctx = ctxv; + const u8 *src = srcv; + u8 *dst = dstv; + u8 *S = ctx->state; + int i = ctx->i, j = ctx->j; + + while ( len-- ) { + i = ( i + 1 ) & 0xff; + j = ( j + S[i] ) & 0xff; + SWAP ( S, i, j ); + if ( srcv && dstv ) + *dst++ = *src++ ^ S[(S[i] + S[j]) & 0xff]; + } + + ctx->i = i; + ctx->j = j; +} + +static void arc4_setiv ( void *ctx __unused, const void *iv __unused ) +{ + /* ARC4 does not use a fixed-length IV */ +} + + +/** + * Perform ARC4 encryption or decryption, skipping initial keystream bytes + * + * @v key ARC4 encryption key + * @v keylen Key length + * @v skip Number of bytes of keystream to skip + * @v src Message to encrypt or decrypt + * @v msglen Length of message + * @ret dst Encrypted or decrypted message + */ +void arc4_skip ( const void *key, size_t keylen, size_t skip, + const void *src, void *dst, size_t msglen ) +{ + struct arc4_ctx ctx; + arc4_setkey ( &ctx, key, keylen ); + arc4_xor ( &ctx, NULL, NULL, skip ); + arc4_xor ( &ctx, src, dst, msglen ); +} + +struct cipher_algorithm arc4_algorithm = { + .name = "ARC4", + .ctxsize = ARC4_CTX_SIZE, + .blocksize = 1, + .setkey = arc4_setkey, + .setiv = arc4_setiv, + .encrypt = arc4_xor, + .decrypt = arc4_xor, +}; -- cgit v1.2.3-55-g7522