[cipher] Add the ARC4 stream cipher

Signed-off-by: Marty Connor <mdc@etherboot.org>

src/crypto/arc4.c

@@ -0,0 +1,131 @@
+/*
+ * 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,
+};

src/include/gpxe/arc4.h

@@ -0,0 +1,22 @@
+#ifndef _GPXE_ARC4_H
+#define _GPXE_ARC4_H
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+struct cipher_algorithm;
+
+#include <stdint.h>
+
+struct arc4_ctx {
+	int i, j;
+	u8 state[256];
+};
+
+#define ARC4_CTX_SIZE sizeof ( struct arc4_ctx )
+
+extern struct cipher_algorithm arc4_algorithm;
+
+void arc4_skip ( const void *key, size_t keylen, size_t skip,
+		 const void *src, void *dst, size_t msglen );
+
+#endif /* _GPXE_ARC4_H */