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-rw-r--r--gpxe/src/crypto/arc4.c131
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diff --git a/gpxe/src/crypto/arc4.c b/gpxe/src/crypto/arc4.c
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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.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <gpxe/crypto.h>
+#include <gpxe/arc4.h>
+
+#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,
+};