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/* | ||
* The ARC4 stream cipher. | ||
* | ||
* Copyright (c) 2009 Joshua Oreman <oremanj@rwcr.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 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. | ||
*/ | ||
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FILE_LICENCE ( GPL2_OR_LATER ); | ||
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#include <gpxe/crypto.h> | ||
#include <gpxe/arc4.h> | ||
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#define SWAP( ary, i, j ) \ | ||
({ u8 temp = ary[i]; ary[i] = ary[j]; ary[j] = temp; }) | ||
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/** | ||
* 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; | ||
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for ( i = 0; i < 256; i++ ) { | ||
S[i] = i; | ||
} | ||
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for ( i = j = 0; i < 256; i++ ) { | ||
j = ( j + S[i] + key[i % keylen] ) & 0xff; | ||
SWAP ( S, i, j ); | ||
} | ||
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ctx->i = ctx->j = 0; | ||
return 0; | ||
} | ||
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/** | ||
* 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; | ||
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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]; | ||
} | ||
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ctx->i = i; | ||
ctx->j = j; | ||
} | ||
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static void arc4_setiv ( void *ctx __unused, const void *iv __unused ) | ||
{ | ||
/* ARC4 does not use a fixed-length IV */ | ||
} | ||
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/** | ||
* 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 ); | ||
} | ||
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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, | ||
}; |
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#ifndef _GPXE_ARC4_H | ||
#define _GPXE_ARC4_H | ||
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FILE_LICENCE ( GPL2_OR_LATER ); | ||
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struct cipher_algorithm; | ||
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#include <stdint.h> | ||
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struct arc4_ctx { | ||
int i, j; | ||
u8 state[256]; | ||
}; | ||
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#define ARC4_CTX_SIZE sizeof ( struct arc4_ctx ) | ||
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extern struct cipher_algorithm arc4_algorithm; | ||
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void arc4_skip ( const void *key, size_t keylen, size_t skip, | ||
const void *src, void *dst, size_t msglen ); | ||
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#endif /* _GPXE_ARC4_H */ |