1/*
  2 * Salsa20: Salsa20 stream cipher algorithm
  3 *
  4 * Copyright (c) 2007 Tan Swee Heng <thesweeheng@gmail.com>
  5 *
  6 * Derived from:
  7 * - salsa20.c: Public domain C code by Daniel J. Bernstein <djb@cr.yp.to>
  8 *
  9 * Salsa20 is a stream cipher candidate in eSTREAM, the ECRYPT Stream
 10 * Cipher Project. It is designed by Daniel J. Bernstein <djb@cr.yp.to>.
 11 * More information about eSTREAM and Salsa20 can be found here:
 12 *   http://www.ecrypt.eu.org/stream/
 13 *   http://cr.yp.to/snuffle.html
 14 *
 15 * This program is free software; you can redistribute it and/or modify it
 16 * under the terms of the GNU General Public License as published by the Free
 17 * Software Foundation; either version 2 of the License, or (at your option)
 18 * any later version.
 19 *
 20 */
 21
 22#include <asm/unaligned.h>
 23#include <crypto/internal/skcipher.h>
 24#include <crypto/salsa20.h>
 25#include <linux/module.h>
 26
 27static void salsa20_block(u32 *state, __le32 *stream)
 28{
 29	u32 x[16];
 30	int i;
 31
 32	memcpy(x, state, sizeof(x));
 33
 34	for (i = 0; i < 20; i += 2) {
 35		x[ 4] ^= rol32((x[ 0] + x[12]),  7);
 36		x[ 8] ^= rol32((x[ 4] + x[ 0]),  9);
 37		x[12] ^= rol32((x[ 8] + x[ 4]), 13);
 38		x[ 0] ^= rol32((x[12] + x[ 8]), 18);
 39		x[ 9] ^= rol32((x[ 5] + x[ 1]),  7);
 40		x[13] ^= rol32((x[ 9] + x[ 5]),  9);
 41		x[ 1] ^= rol32((x[13] + x[ 9]), 13);
 42		x[ 5] ^= rol32((x[ 1] + x[13]), 18);
 43		x[14] ^= rol32((x[10] + x[ 6]),  7);
 44		x[ 2] ^= rol32((x[14] + x[10]),  9);
 45		x[ 6] ^= rol32((x[ 2] + x[14]), 13);
 46		x[10] ^= rol32((x[ 6] + x[ 2]), 18);
 47		x[ 3] ^= rol32((x[15] + x[11]),  7);
 48		x[ 7] ^= rol32((x[ 3] + x[15]),  9);
 49		x[11] ^= rol32((x[ 7] + x[ 3]), 13);
 50		x[15] ^= rol32((x[11] + x[ 7]), 18);
 51		x[ 1] ^= rol32((x[ 0] + x[ 3]),  7);
 52		x[ 2] ^= rol32((x[ 1] + x[ 0]),  9);
 53		x[ 3] ^= rol32((x[ 2] + x[ 1]), 13);
 54		x[ 0] ^= rol32((x[ 3] + x[ 2]), 18);
 55		x[ 6] ^= rol32((x[ 5] + x[ 4]),  7);
 56		x[ 7] ^= rol32((x[ 6] + x[ 5]),  9);
 57		x[ 4] ^= rol32((x[ 7] + x[ 6]), 13);
 58		x[ 5] ^= rol32((x[ 4] + x[ 7]), 18);
 59		x[11] ^= rol32((x[10] + x[ 9]),  7);
 60		x[ 8] ^= rol32((x[11] + x[10]),  9);
 61		x[ 9] ^= rol32((x[ 8] + x[11]), 13);
 62		x[10] ^= rol32((x[ 9] + x[ 8]), 18);
 63		x[12] ^= rol32((x[15] + x[14]),  7);
 64		x[13] ^= rol32((x[12] + x[15]),  9);
 65		x[14] ^= rol32((x[13] + x[12]), 13);
 66		x[15] ^= rol32((x[14] + x[13]), 18);
 67	}
 68
 69	for (i = 0; i < 16; i++)
 70		stream[i] = cpu_to_le32(x[i] + state[i]);
 71
 72	if (++state[8] == 0)
 73		state[9]++;
 74}
 75
 76static void salsa20_docrypt(u32 *state, u8 *dst, const u8 *src,
 77			    unsigned int bytes)
 78{
 79	__le32 stream[SALSA20_BLOCK_SIZE / sizeof(__le32)];
 80
 81	if (dst != src)
 82		memcpy(dst, src, bytes);
 83
 84	while (bytes >= SALSA20_BLOCK_SIZE) {
 85		salsa20_block(state, stream);
 86		crypto_xor(dst, (const u8 *)stream, SALSA20_BLOCK_SIZE);
 87		bytes -= SALSA20_BLOCK_SIZE;
 88		dst += SALSA20_BLOCK_SIZE;
 89	}
 90	if (bytes) {
 91		salsa20_block(state, stream);
 92		crypto_xor(dst, (const u8 *)stream, bytes);
 93	}
 94}
 95
 96void crypto_salsa20_init(u32 *state, const struct salsa20_ctx *ctx,
 97			 const u8 *iv)
 98{
 99	memcpy(state, ctx->initial_state, sizeof(ctx->initial_state));
100	state[6] = get_unaligned_le32(iv + 0);
101	state[7] = get_unaligned_le32(iv + 4);
102}
103EXPORT_SYMBOL_GPL(crypto_salsa20_init);
104
105int crypto_salsa20_setkey(struct crypto_skcipher *tfm, const u8 *key,
106			  unsigned int keysize)
107{
108	static const char sigma[16] = "expand 32-byte k";
109	static const char tau[16] = "expand 16-byte k";
110	struct salsa20_ctx *ctx = crypto_skcipher_ctx(tfm);
111	const char *constants;
112
113	if (keysize != SALSA20_MIN_KEY_SIZE &&
114	    keysize != SALSA20_MAX_KEY_SIZE)
115		return -EINVAL;
116
117	ctx->initial_state[1] = get_unaligned_le32(key + 0);
118	ctx->initial_state[2] = get_unaligned_le32(key + 4);
119	ctx->initial_state[3] = get_unaligned_le32(key + 8);
120	ctx->initial_state[4] = get_unaligned_le32(key + 12);
121	if (keysize == 32) { /* recommended */
122		key += 16;
123		constants = sigma;
124	} else { /* keysize == 16 */
125		constants = tau;
126	}
127	ctx->initial_state[11] = get_unaligned_le32(key + 0);
128	ctx->initial_state[12] = get_unaligned_le32(key + 4);
129	ctx->initial_state[13] = get_unaligned_le32(key + 8);
130	ctx->initial_state[14] = get_unaligned_le32(key + 12);
131	ctx->initial_state[0]  = get_unaligned_le32(constants + 0);
132	ctx->initial_state[5]  = get_unaligned_le32(constants + 4);
133	ctx->initial_state[10] = get_unaligned_le32(constants + 8);
134	ctx->initial_state[15] = get_unaligned_le32(constants + 12);
135
136	/* space for the nonce; it will be overridden for each request */
137	ctx->initial_state[6] = 0;
138	ctx->initial_state[7] = 0;
139
140	/* initial block number */
141	ctx->initial_state[8] = 0;
142	ctx->initial_state[9] = 0;
143
144	return 0;
145}
146EXPORT_SYMBOL_GPL(crypto_salsa20_setkey);
147
148static int salsa20_crypt(struct skcipher_request *req)
149{
150	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
151	const struct salsa20_ctx *ctx = crypto_skcipher_ctx(tfm);
152	struct skcipher_walk walk;
153	u32 state[16];
154	int err;
155
156	err = skcipher_walk_virt(&walk, req, true);
157
158	crypto_salsa20_init(state, ctx, walk.iv);
159
160	while (walk.nbytes > 0) {
161		unsigned int nbytes = walk.nbytes;
162
163		if (nbytes < walk.total)
164			nbytes = round_down(nbytes, walk.stride);
165
166		salsa20_docrypt(state, walk.dst.virt.addr, walk.src.virt.addr,
167				nbytes);
168		err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
169	}
170
171	return err;
172}
173
174static struct skcipher_alg alg = {
175	.base.cra_name		= "salsa20",
176	.base.cra_driver_name	= "salsa20-generic",
177	.base.cra_priority	= 100,
178	.base.cra_blocksize	= 1,
179	.base.cra_ctxsize	= sizeof(struct salsa20_ctx),
180	.base.cra_module	= THIS_MODULE,
181
182	.min_keysize		= SALSA20_MIN_KEY_SIZE,
183	.max_keysize		= SALSA20_MAX_KEY_SIZE,
184	.ivsize			= SALSA20_IV_SIZE,
185	.chunksize		= SALSA20_BLOCK_SIZE,
186	.setkey			= crypto_salsa20_setkey,
187	.encrypt		= salsa20_crypt,
188	.decrypt		= salsa20_crypt,
189};
190
191static int __init salsa20_generic_mod_init(void)
192{
193	return crypto_register_skcipher(&alg);
194}
195
196static void __exit salsa20_generic_mod_fini(void)
197{
198	crypto_unregister_skcipher(&alg);
199}
200
201module_init(salsa20_generic_mod_init);
202module_exit(salsa20_generic_mod_fini);
203
204MODULE_LICENSE("GPL");
205MODULE_DESCRIPTION ("Salsa20 stream cipher algorithm");
206MODULE_ALIAS_CRYPTO("salsa20");
207MODULE_ALIAS_CRYPTO("salsa20-generic");