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/*
* Salsa20: Salsa20 stream cipher algorithm
*
* Copyright (c) 2007 Tan Swee Heng <thesweeheng@gmail.com>
*
* Derived from:
* - salsa20.c: Public domain C code by Daniel J. Bernstein <djb@cr.yp.to>
*
* Salsa20 is a stream cipher candidate in eSTREAM, the ECRYPT Stream
* Cipher Project. It is designed by Daniel J. Bernstein <djb@cr.yp.to>.
* More information about eSTREAM and Salsa20 can be found here:
* http://www.ecrypt.eu.org/stream/
* http://cr.yp.to/snuffle.html
*
* 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 (at your option)
* any later version.
*
*/
#include <linux/init.h>
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/crypto.h>
#include <linux/types.h>
#include <crypto/algapi.h>
#include <asm/byteorder.h>
#define SALSA20_IV_SIZE 8U
#define SALSA20_MIN_KEY_SIZE 16U
#define SALSA20_MAX_KEY_SIZE 32U
/*
* Start of code taken from D. J. Bernstein's reference implementation.
* With some modifications and optimizations made to suit our needs.
*/
/*
salsa20-ref.c version 20051118
D. J. Bernstein
Public domain.
*/
#define ROTATE(v,n) (((v) << (n)) | ((v) >> (32 - (n))))
#define XOR(v,w) ((v) ^ (w))
#define PLUS(v,w) (((v) + (w)))
#define PLUSONE(v) (PLUS((v),1))
#define U32TO8_LITTLE(p, v) \
{ (p)[0] = (v >> 0) & 0xff; (p)[1] = (v >> 8) & 0xff; \
(p)[2] = (v >> 16) & 0xff; (p)[3] = (v >> 24) & 0xff; }
#define U8TO32_LITTLE(p) \
(((u32)((p)[0]) ) | ((u32)((p)[1]) << 8) | \
((u32)((p)[2]) << 16) | ((u32)((p)[3]) << 24) )
struct salsa20_ctx
{
u32 input[16];
};
static void salsa20_wordtobyte(u8 output[64], const u32 input[16])
{
u32 x[16];
int i;
memcpy(x, input, sizeof(x));
for (i = 20; i > 0; i -= 2) {
x[ 4] = XOR(x[ 4],ROTATE(PLUS(x[ 0],x[12]), 7));
x[ 8] = XOR(x[ 8],ROTATE(PLUS(x[ 4],x[ 0]), 9));
x[12] = XOR(x[12],ROTATE(PLUS(x[ 8],x[ 4]),13));
x[ 0] = XOR(x[ 0],ROTATE(PLUS(x[12],x[ 8]),18));
x[ 9] = XOR(x[ 9],ROTATE(PLUS(x[ 5],x[ 1]), 7));
x[13] = XOR(x[13],ROTATE(PLUS(x[ 9],x[ 5]), 9));
x[ 1] = XOR(x[ 1],ROTATE(PLUS(x[13],x[ 9]),13));
x[ 5] = XOR(x[ 5],ROTATE(PLUS(x[ 1],x[13]),18));
x[14] = XOR(x[14],ROTATE(PLUS(x[10],x[ 6]), 7));
x[ 2] = XOR(x[ 2],ROTATE(PLUS(x[14],x[10]), 9));
x[ 6] = XOR(x[ 6],ROTATE(PLUS(x[ 2],x[14]),13));
x[10] = XOR(x[10],ROTATE(PLUS(x[ 6],x[ 2]),18));
x[ 3] = XOR(x[ 3],ROTATE(PLUS(x[15],x[11]), 7));
x[ 7] = XOR(x[ 7],ROTATE(PLUS(x[ 3],x[15]), 9));
x[11] = XOR(x[11],ROTATE(PLUS(x[ 7],x[ 3]),13));
x[15] = XOR(x[15],ROTATE(PLUS(x[11],x[ 7]),18));
x[ 1] = XOR(x[ 1],ROTATE(PLUS(x[ 0],x[ 3]), 7));
x[ 2] = XOR(x[ 2],ROTATE(PLUS(x[ 1],x[ 0]), 9));
x[ 3] = XOR(x[ 3],ROTATE(PLUS(x[ 2],x[ 1]),13));
x[ 0] = XOR(x[ 0],ROTATE(PLUS(x[ 3],x[ 2]),18));
x[ 6] = XOR(x[ 6],ROTATE(PLUS(x[ 5],x[ 4]), 7));
x[ 7] = XOR(x[ 7],ROTATE(PLUS(x[ 6],x[ 5]), 9));
x[ 4] = XOR(x[ 4],ROTATE(PLUS(x[ 7],x[ 6]),13));
x[ 5] = XOR(x[ 5],ROTATE(PLUS(x[ 4],x[ 7]),18));
x[11] = XOR(x[11],ROTATE(PLUS(x[10],x[ 9]), 7));
x[ 8] = XOR(x[ 8],ROTATE(PLUS(x[11],x[10]), 9));
x[ 9] = XOR(x[ 9],ROTATE(PLUS(x[ 8],x[11]),13));
x[10] = XOR(x[10],ROTATE(PLUS(x[ 9],x[ 8]),18));
x[12] = XOR(x[12],ROTATE(PLUS(x[15],x[14]), 7));
x[13] = XOR(x[13],ROTATE(PLUS(x[12],x[15]), 9));
x[14] = XOR(x[14],ROTATE(PLUS(x[13],x[12]),13));
x[15] = XOR(x[15],ROTATE(PLUS(x[14],x[13]),18));
}
for (i = 0; i < 16; ++i)
x[i] = PLUS(x[i],input[i]);
for (i = 0; i < 16; ++i)
U32TO8_LITTLE(output + 4 * i,x[i]);
}
static const char sigma[16] = "expand 32-byte k";
static const char tau[16] = "expand 16-byte k";
static void salsa20_keysetup(struct salsa20_ctx *ctx, const u8 *k, u32 kbytes)
{
const char *constants;
ctx->input[1] = U8TO32_LITTLE(k + 0);
ctx->input[2] = U8TO32_LITTLE(k + 4);
ctx->input[3] = U8TO32_LITTLE(k + 8);
ctx->input[4] = U8TO32_LITTLE(k + 12);
if (kbytes == 32) { /* recommended */
k += 16;
constants = sigma;
} else { /* kbytes == 16 */
constants = tau;
}
ctx->input[11] = U8TO32_LITTLE(k + 0);
ctx->input[12] = U8TO32_LITTLE(k + 4);
ctx->input[13] = U8TO32_LITTLE(k + 8);
ctx->input[14] = U8TO32_LITTLE(k + 12);
ctx->input[0] = U8TO32_LITTLE(constants + 0);
ctx->input[5] = U8TO32_LITTLE(constants + 4);
ctx->input[10] = U8TO32_LITTLE(constants + 8);
ctx->input[15] = U8TO32_LITTLE(constants + 12);
}
static void salsa20_ivsetup(struct salsa20_ctx *ctx, const u8 *iv)
{
ctx->input[6] = U8TO32_LITTLE(iv + 0);
ctx->input[7] = U8TO32_LITTLE(iv + 4);
ctx->input[8] = 0;
ctx->input[9] = 0;
}
static void salsa20_encrypt_bytes(struct salsa20_ctx *ctx, u8 *dst,
const u8 *src, unsigned int bytes)
{
u8 buf[64];
if (dst != src)
memcpy(dst, src, bytes);
while (bytes) {
salsa20_wordtobyte(buf, ctx->input);
ctx->input[8] = PLUSONE(ctx->input[8]);
if (!ctx->input[8])
ctx->input[9] = PLUSONE(ctx->input[9]);
if (bytes <= 64) {
crypto_xor(dst, buf, bytes);
return;
}
crypto_xor(dst, buf, 64);
bytes -= 64;
dst += 64;
}
}
/*
* End of code taken from D. J. Bernstein's reference implementation.
*/
static int setkey(struct crypto_tfm *tfm, const u8 *key,
unsigned int keysize)
{
struct salsa20_ctx *ctx = crypto_tfm_ctx(tfm);
salsa20_keysetup(ctx, key, keysize);
return 0;
}
static int encrypt(struct blkcipher_desc *desc,
struct scatterlist *dst, struct scatterlist *src,
unsigned int nbytes)
{
struct blkcipher_walk walk;
struct crypto_blkcipher *tfm = desc->tfm;
struct salsa20_ctx *ctx = crypto_blkcipher_ctx(tfm);
int err;
blkcipher_walk_init(&walk, dst, src, nbytes);
err = blkcipher_walk_virt_block(desc, &walk, 64);
salsa20_ivsetup(ctx, walk.iv);
if (likely(walk.nbytes == nbytes))
{
salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,
walk.src.virt.addr, nbytes);
return blkcipher_walk_done(desc, &walk, 0);
}
while (walk.nbytes >= 64) {
salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,
walk.src.virt.addr,
walk.nbytes - (walk.nbytes % 64));
err = blkcipher_walk_done(desc, &walk, walk.nbytes % 64);
}
if (walk.nbytes) {
salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,
walk.src.virt.addr, walk.nbytes);
err = blkcipher_walk_done(desc, &walk, 0);
}
return err;
}
static struct crypto_alg alg = {
.cra_name = "salsa20",
.cra_driver_name = "salsa20-generic",
.cra_priority = 100,
.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER,
.cra_type = &crypto_blkcipher_type,
.cra_blocksize = 1,
.cra_ctxsize = sizeof(struct salsa20_ctx),
.cra_alignmask = 3,
.cra_module = THIS_MODULE,
.cra_list = LIST_HEAD_INIT(alg.cra_list),
.cra_u = {
.blkcipher = {
.setkey = setkey,
.encrypt = encrypt,
.decrypt = encrypt,
.min_keysize = SALSA20_MIN_KEY_SIZE,
.max_keysize = SALSA20_MAX_KEY_SIZE,
.ivsize = SALSA20_IV_SIZE,
}
}
};
static int __init salsa20_generic_mod_init(void)
{
return crypto_register_alg(&alg);
}
static void __exit salsa20_generic_mod_fini(void)
{
crypto_unregister_alg(&alg);
}
module_init(salsa20_generic_mod_init);
module_exit(salsa20_generic_mod_fini);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION ("Salsa20 stream cipher algorithm");
MODULE_ALIAS("salsa20");
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