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 <linux/module.h>
 25
 26#define SALSA20_IV_SIZE        8
 27#define SALSA20_MIN_KEY_SIZE  16
 28#define SALSA20_MAX_KEY_SIZE  32
 29#define SALSA20_BLOCK_SIZE    64
 30
 31struct salsa20_ctx {
 32	u32 initial_state[16];
 33};
 34
 35static void salsa20_block(u32 *state, __le32 *stream)
 36{
 37	u32 x[16];
 38	int i;
 39
 40	memcpy(x, state, sizeof(x));
 41
 42	for (i = 0; i < 20; i += 2) {
 43		x[ 4] ^= rol32((x[ 0] + x[12]),  7);
 44		x[ 8] ^= rol32((x[ 4] + x[ 0]),  9);
 45		x[12] ^= rol32((x[ 8] + x[ 4]), 13);
 46		x[ 0] ^= rol32((x[12] + x[ 8]), 18);
 47		x[ 9] ^= rol32((x[ 5] + x[ 1]),  7);
 48		x[13] ^= rol32((x[ 9] + x[ 5]),  9);
 49		x[ 1] ^= rol32((x[13] + x[ 9]), 13);
 50		x[ 5] ^= rol32((x[ 1] + x[13]), 18);
 51		x[14] ^= rol32((x[10] + x[ 6]),  7);
 52		x[ 2] ^= rol32((x[14] + x[10]),  9);
 53		x[ 6] ^= rol32((x[ 2] + x[14]), 13);
 54		x[10] ^= rol32((x[ 6] + x[ 2]), 18);
 55		x[ 3] ^= rol32((x[15] + x[11]),  7);
 56		x[ 7] ^= rol32((x[ 3] + x[15]),  9);
 57		x[11] ^= rol32((x[ 7] + x[ 3]), 13);
 58		x[15] ^= rol32((x[11] + x[ 7]), 18);
 59		x[ 1] ^= rol32((x[ 0] + x[ 3]),  7);
 60		x[ 2] ^= rol32((x[ 1] + x[ 0]),  9);
 61		x[ 3] ^= rol32((x[ 2] + x[ 1]), 13);
 62		x[ 0] ^= rol32((x[ 3] + x[ 2]), 18);
 63		x[ 6] ^= rol32((x[ 5] + x[ 4]),  7);
 64		x[ 7] ^= rol32((x[ 6] + x[ 5]),  9);
 65		x[ 4] ^= rol32((x[ 7] + x[ 6]), 13);
 66		x[ 5] ^= rol32((x[ 4] + x[ 7]), 18);
 67		x[11] ^= rol32((x[10] + x[ 9]),  7);
 68		x[ 8] ^= rol32((x[11] + x[10]),  9);
 69		x[ 9] ^= rol32((x[ 8] + x[11]), 13);
 70		x[10] ^= rol32((x[ 9] + x[ 8]), 18);
 71		x[12] ^= rol32((x[15] + x[14]),  7);
 72		x[13] ^= rol32((x[12] + x[15]),  9);
 73		x[14] ^= rol32((x[13] + x[12]), 13);
 74		x[15] ^= rol32((x[14] + x[13]), 18);
 75	}
 76
 77	for (i = 0; i < 16; i++)
 78		stream[i] = cpu_to_le32(x[i] + state[i]);
 79
 80	if (++state[8] == 0)
 81		state[9]++;
 82}
 83
 84static void salsa20_docrypt(u32 *state, u8 *dst, const u8 *src,
 85			    unsigned int bytes)
 86{
 87	__le32 stream[SALSA20_BLOCK_SIZE / sizeof(__le32)];
 88
 89	while (bytes >= SALSA20_BLOCK_SIZE) {
 90		salsa20_block(state, stream);
 91		crypto_xor_cpy(dst, src, (const u8 *)stream,
 92			       SALSA20_BLOCK_SIZE);
 93		bytes -= SALSA20_BLOCK_SIZE;
 94		dst += SALSA20_BLOCK_SIZE;
 95		src += SALSA20_BLOCK_SIZE;
 96	}
 97	if (bytes) {
 98		salsa20_block(state, stream);
 99		crypto_xor_cpy(dst, src, (const u8 *)stream, bytes);
100	}
101}
102
103static void salsa20_init(u32 *state, const struct salsa20_ctx *ctx,
104			 const u8 *iv)
105{
106	memcpy(state, ctx->initial_state, sizeof(ctx->initial_state));
107	state[6] = get_unaligned_le32(iv + 0);
108	state[7] = get_unaligned_le32(iv + 4);
109}
110
111static int salsa20_setkey(struct crypto_skcipher *tfm, const u8 *key,
112			  unsigned int keysize)
113{
114	static const char sigma[16] = "expand 32-byte k";
115	static const char tau[16] = "expand 16-byte k";
116	struct salsa20_ctx *ctx = crypto_skcipher_ctx(tfm);
117	const char *constants;
118
119	if (keysize != SALSA20_MIN_KEY_SIZE &&
120	    keysize != SALSA20_MAX_KEY_SIZE)
121		return -EINVAL;
122
123	ctx->initial_state[1] = get_unaligned_le32(key + 0);
124	ctx->initial_state[2] = get_unaligned_le32(key + 4);
125	ctx->initial_state[3] = get_unaligned_le32(key + 8);
126	ctx->initial_state[4] = get_unaligned_le32(key + 12);
127	if (keysize == 32) { /* recommended */
128		key += 16;
129		constants = sigma;
130	} else { /* keysize == 16 */
131		constants = tau;
132	}
133	ctx->initial_state[11] = get_unaligned_le32(key + 0);
134	ctx->initial_state[12] = get_unaligned_le32(key + 4);
135	ctx->initial_state[13] = get_unaligned_le32(key + 8);
136	ctx->initial_state[14] = get_unaligned_le32(key + 12);
137	ctx->initial_state[0]  = get_unaligned_le32(constants + 0);
138	ctx->initial_state[5]  = get_unaligned_le32(constants + 4);
139	ctx->initial_state[10] = get_unaligned_le32(constants + 8);
140	ctx->initial_state[15] = get_unaligned_le32(constants + 12);
141
142	/* space for the nonce; it will be overridden for each request */
143	ctx->initial_state[6] = 0;
144	ctx->initial_state[7] = 0;
145
146	/* initial block number */
147	ctx->initial_state[8] = 0;
148	ctx->initial_state[9] = 0;
149
150	return 0;
151}
152
153static int salsa20_crypt(struct skcipher_request *req)
154{
155	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
156	const struct salsa20_ctx *ctx = crypto_skcipher_ctx(tfm);
157	struct skcipher_walk walk;
158	u32 state[16];
159	int err;
160
161	err = skcipher_walk_virt(&walk, req, false);
162
163	salsa20_init(state, ctx, req->iv);
164
165	while (walk.nbytes > 0) {
166		unsigned int nbytes = walk.nbytes;
167
168		if (nbytes < walk.total)
169			nbytes = round_down(nbytes, walk.stride);
170
171		salsa20_docrypt(state, walk.dst.virt.addr, walk.src.virt.addr,
172				nbytes);
173		err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
174	}
175
176	return err;
177}
178
179static struct skcipher_alg alg = {
180	.base.cra_name		= "salsa20",
181	.base.cra_driver_name	= "salsa20-generic",
182	.base.cra_priority	= 100,
183	.base.cra_blocksize	= 1,
184	.base.cra_ctxsize	= sizeof(struct salsa20_ctx),
185	.base.cra_module	= THIS_MODULE,
186
187	.min_keysize		= SALSA20_MIN_KEY_SIZE,
188	.max_keysize		= SALSA20_MAX_KEY_SIZE,
189	.ivsize			= SALSA20_IV_SIZE,
190	.chunksize		= SALSA20_BLOCK_SIZE,
191	.setkey			= salsa20_setkey,
192	.encrypt		= salsa20_crypt,
193	.decrypt		= salsa20_crypt,
194};
195
196static int __init salsa20_generic_mod_init(void)
197{
198	return crypto_register_skcipher(&alg);
199}
200
201static void __exit salsa20_generic_mod_fini(void)
202{
203	crypto_unregister_skcipher(&alg);
204}
205
206subsys_initcall(salsa20_generic_mod_init);
207module_exit(salsa20_generic_mod_fini);
208
209MODULE_LICENSE("GPL");
210MODULE_DESCRIPTION ("Salsa20 stream cipher algorithm");
211MODULE_ALIAS_CRYPTO("salsa20");
212MODULE_ALIAS_CRYPTO("salsa20-generic");