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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:
* https://www.ecrypt.eu.org/stream/
* https://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 <asm/unaligned.h>
#include <crypto/internal/skcipher.h>
#include <linux/module.h>
#define SALSA20_IV_SIZE 8
#define SALSA20_MIN_KEY_SIZE 16
#define SALSA20_MAX_KEY_SIZE 32
#define SALSA20_BLOCK_SIZE 64
struct salsa20_ctx {
u32 initial_state[16];
};
static void salsa20_block(u32 *state, __le32 *stream)
{
u32 x[16];
int i;
memcpy(x, state, sizeof(x));
for (i = 0; i < 20; i += 2) {
x[ 4] ^= rol32((x[ 0] + x[12]), 7);
x[ 8] ^= rol32((x[ 4] + x[ 0]), 9);
x[12] ^= rol32((x[ 8] + x[ 4]), 13);
x[ 0] ^= rol32((x[12] + x[ 8]), 18);
x[ 9] ^= rol32((x[ 5] + x[ 1]), 7);
x[13] ^= rol32((x[ 9] + x[ 5]), 9);
x[ 1] ^= rol32((x[13] + x[ 9]), 13);
x[ 5] ^= rol32((x[ 1] + x[13]), 18);
x[14] ^= rol32((x[10] + x[ 6]), 7);
x[ 2] ^= rol32((x[14] + x[10]), 9);
x[ 6] ^= rol32((x[ 2] + x[14]), 13);
x[10] ^= rol32((x[ 6] + x[ 2]), 18);
x[ 3] ^= rol32((x[15] + x[11]), 7);
x[ 7] ^= rol32((x[ 3] + x[15]), 9);
x[11] ^= rol32((x[ 7] + x[ 3]), 13);
x[15] ^= rol32((x[11] + x[ 7]), 18);
x[ 1] ^= rol32((x[ 0] + x[ 3]), 7);
x[ 2] ^= rol32((x[ 1] + x[ 0]), 9);
x[ 3] ^= rol32((x[ 2] + x[ 1]), 13);
x[ 0] ^= rol32((x[ 3] + x[ 2]), 18);
x[ 6] ^= rol32((x[ 5] + x[ 4]), 7);
x[ 7] ^= rol32((x[ 6] + x[ 5]), 9);
x[ 4] ^= rol32((x[ 7] + x[ 6]), 13);
x[ 5] ^= rol32((x[ 4] + x[ 7]), 18);
x[11] ^= rol32((x[10] + x[ 9]), 7);
x[ 8] ^= rol32((x[11] + x[10]), 9);
x[ 9] ^= rol32((x[ 8] + x[11]), 13);
x[10] ^= rol32((x[ 9] + x[ 8]), 18);
x[12] ^= rol32((x[15] + x[14]), 7);
x[13] ^= rol32((x[12] + x[15]), 9);
x[14] ^= rol32((x[13] + x[12]), 13);
x[15] ^= rol32((x[14] + x[13]), 18);
}
for (i = 0; i < 16; i++)
stream[i] = cpu_to_le32(x[i] + state[i]);
if (++state[8] == 0)
state[9]++;
}
static void salsa20_docrypt(u32 *state, u8 *dst, const u8 *src,
unsigned int bytes)
{
__le32 stream[SALSA20_BLOCK_SIZE / sizeof(__le32)];
while (bytes >= SALSA20_BLOCK_SIZE) {
salsa20_block(state, stream);
crypto_xor_cpy(dst, src, (const u8 *)stream,
SALSA20_BLOCK_SIZE);
bytes -= SALSA20_BLOCK_SIZE;
dst += SALSA20_BLOCK_SIZE;
src += SALSA20_BLOCK_SIZE;
}
if (bytes) {
salsa20_block(state, stream);
crypto_xor_cpy(dst, src, (const u8 *)stream, bytes);
}
}
static void salsa20_init(u32 *state, const struct salsa20_ctx *ctx,
const u8 *iv)
{
memcpy(state, ctx->initial_state, sizeof(ctx->initial_state));
state[6] = get_unaligned_le32(iv + 0);
state[7] = get_unaligned_le32(iv + 4);
}
static int salsa20_setkey(struct crypto_skcipher *tfm, const u8 *key,
unsigned int keysize)
{
static const char sigma[16] = "expand 32-byte k";
static const char tau[16] = "expand 16-byte k";
struct salsa20_ctx *ctx = crypto_skcipher_ctx(tfm);
const char *constants;
if (keysize != SALSA20_MIN_KEY_SIZE &&
keysize != SALSA20_MAX_KEY_SIZE)
return -EINVAL;
ctx->initial_state[1] = get_unaligned_le32(key + 0);
ctx->initial_state[2] = get_unaligned_le32(key + 4);
ctx->initial_state[3] = get_unaligned_le32(key + 8);
ctx->initial_state[4] = get_unaligned_le32(key + 12);
if (keysize == 32) { /* recommended */
key += 16;
constants = sigma;
} else { /* keysize == 16 */
constants = tau;
}
ctx->initial_state[11] = get_unaligned_le32(key + 0);
ctx->initial_state[12] = get_unaligned_le32(key + 4);
ctx->initial_state[13] = get_unaligned_le32(key + 8);
ctx->initial_state[14] = get_unaligned_le32(key + 12);
ctx->initial_state[0] = get_unaligned_le32(constants + 0);
ctx->initial_state[5] = get_unaligned_le32(constants + 4);
ctx->initial_state[10] = get_unaligned_le32(constants + 8);
ctx->initial_state[15] = get_unaligned_le32(constants + 12);
/* space for the nonce; it will be overridden for each request */
ctx->initial_state[6] = 0;
ctx->initial_state[7] = 0;
/* initial block number */
ctx->initial_state[8] = 0;
ctx->initial_state[9] = 0;
return 0;
}
static int salsa20_crypt(struct skcipher_request *req)
{
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
const struct salsa20_ctx *ctx = crypto_skcipher_ctx(tfm);
struct skcipher_walk walk;
u32 state[16];
int err;
err = skcipher_walk_virt(&walk, req, false);
salsa20_init(state, ctx, req->iv);
while (walk.nbytes > 0) {
unsigned int nbytes = walk.nbytes;
if (nbytes < walk.total)
nbytes = round_down(nbytes, walk.stride);
salsa20_docrypt(state, walk.dst.virt.addr, walk.src.virt.addr,
nbytes);
err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
}
return err;
}
static struct skcipher_alg alg = {
.base.cra_name = "salsa20",
.base.cra_driver_name = "salsa20-generic",
.base.cra_priority = 100,
.base.cra_blocksize = 1,
.base.cra_ctxsize = sizeof(struct salsa20_ctx),
.base.cra_module = THIS_MODULE,
.min_keysize = SALSA20_MIN_KEY_SIZE,
.max_keysize = SALSA20_MAX_KEY_SIZE,
.ivsize = SALSA20_IV_SIZE,
.chunksize = SALSA20_BLOCK_SIZE,
.setkey = salsa20_setkey,
.encrypt = salsa20_crypt,
.decrypt = salsa20_crypt,
};
static int __init salsa20_generic_mod_init(void)
{
return crypto_register_skcipher(&alg);
}
static void __exit salsa20_generic_mod_fini(void)
{
crypto_unregister_skcipher(&alg);
}
subsys_initcall(salsa20_generic_mod_init);
module_exit(salsa20_generic_mod_fini);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION ("Salsa20 stream cipher algorithm");
MODULE_ALIAS_CRYPTO("salsa20");
MODULE_ALIAS_CRYPTO("salsa20-generic");
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