/*
* Cryptographic API
*
* ARC4 Cipher Algorithm
*
* Jon Oberheide <jon@oberheide.org>
*
* This program is free software; you can redistribute it and/or modify
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
*/

#include <linux/module.h>
#include <linux/init.h>
#include <linux/crypto.h>
#include <crypto/algapi.h>

#define ARC4_MIN_KEY_SIZE	1
#define ARC4_MAX_KEY_SIZE	256
#define ARC4_BLOCK_SIZE		1

struct arc4_ctx {
u32 S[256];
u32 x, y;
};

static int arc4_set_key(struct crypto_tfm *tfm, const u8 *in_key,
unsigned int key_len)
{
struct arc4_ctx *ctx = crypto_tfm_ctx(tfm);
int i, j = 0, k = 0;

ctx->x = 1;
ctx->y = 0;

for (i = 0; i < 256; i++)
ctx->S[i] = i;

for (i = 0; i < 256; i++) {
u32 a = ctx->S[i];
j = (j + in_key[k] + a) & 0xff;
ctx->S[i] = ctx->S[j];
ctx->S[j] = a;
if (++k >= key_len)
k = 0;
}

return 0;
}

static void arc4_crypt(struct arc4_ctx *ctx, u8 *out, const u8 *in,
unsigned int len)
{
u32 *const S = ctx->S;
u32 x, y, a, b;
u32 ty, ta, tb;

if (len == 0)
return;

x = ctx->x;
y = ctx->y;

a = S[x];
y = (y + a) & 0xff;
b = S[y];

do {
S[y] = a;
a = (a + b) & 0xff;
S[x] = b;
x = (x + 1) & 0xff;
ta = S[x];
ty = (y + ta) & 0xff;
tb = S[ty];
*out++ = *in++ ^ S[a];
if (--len == 0)
break;
y = ty;
a = ta;
b = tb;
} while (true);

ctx->x = x;
ctx->y = y;
}

static void arc4_crypt_one(struct crypto_tfm *tfm, u8 *out, const u8 *in)
{
arc4_crypt(crypto_tfm_ctx(tfm), out, in, 1);
}

static int ecb_arc4_crypt(struct blkcipher_desc *desc, struct scatterlist *dst,
struct scatterlist *src, unsigned int nbytes)
{
struct arc4_ctx *ctx = crypto_blkcipher_ctx(desc->tfm);
struct blkcipher_walk walk;
int err;

blkcipher_walk_init(&walk, dst, src, nbytes);

err = blkcipher_walk_virt(desc, &walk);

while (walk.nbytes > 0) {

arc4_crypt(ctx, wdst, wsrc, walk.nbytes);

err = blkcipher_walk_done(desc, &walk, 0);
}

return err;
}

static struct crypto_alg arc4_algs[2] = { {
.cra_name		=	"arc4",
.cra_flags		=	CRYPTO_ALG_TYPE_CIPHER,
.cra_blocksize		=	ARC4_BLOCK_SIZE,
.cra_ctxsize		=	sizeof(struct arc4_ctx),
.cra_module		=	THIS_MODULE,
.cra_u			=	{
.cipher = {
.cia_min_keysize	=	ARC4_MIN_KEY_SIZE,
.cia_max_keysize	=	ARC4_MAX_KEY_SIZE,
.cia_setkey		=	arc4_set_key,
.cia_encrypt		=	arc4_crypt_one,
.cia_decrypt		=	arc4_crypt_one,
},
},
}, {
.cra_name		=	"ecb(arc4)",
.cra_priority		=	100,
.cra_flags		=	CRYPTO_ALG_TYPE_BLKCIPHER,
.cra_blocksize		=	ARC4_BLOCK_SIZE,
.cra_ctxsize		=	sizeof(struct arc4_ctx),
.cra_type		=	&crypto_blkcipher_type,
.cra_module		=	THIS_MODULE,
.cra_u			=	{
.blkcipher = {
.min_keysize	=	ARC4_MIN_KEY_SIZE,
.max_keysize	=	ARC4_MAX_KEY_SIZE,
.setkey		=	arc4_set_key,
.encrypt	=	ecb_arc4_crypt,
.decrypt	=	ecb_arc4_crypt,
},
},
} };

static int __init arc4_init(void)
{
return crypto_register_algs(arc4_algs, ARRAY_SIZE(arc4_algs));
}

static void __exit arc4_exit(void)
{
crypto_unregister_algs(arc4_algs, ARRAY_SIZE(arc4_algs));
}

module_init(arc4_init);
module_exit(arc4_exit);