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 <linux/init.h>
23#include <linux/module.h>
24#include <linux/errno.h>
25#include <linux/crypto.h>
26#include <linux/types.h>
27#include <linux/bitops.h>
28#include <crypto/algapi.h>
29#include <asm/byteorder.h>
30
31#define SALSA20_IV_SIZE        8U
32#define SALSA20_MIN_KEY_SIZE  16U
33#define SALSA20_MAX_KEY_SIZE  32U
34
35/*
36 * Start of code taken from D. J. Bernstein's reference implementation.
37 * With some modifications and optimizations made to suit our needs.
38 */
39
40/*
41salsa20-ref.c version 20051118
42D. J. Bernstein
43Public domain.
44*/
45
46#define U32TO8_LITTLE(p, v) \
47	{ (p)[0] = (v >>  0) & 0xff; (p)[1] = (v >>  8) & 0xff; \
48	  (p)[2] = (v >> 16) & 0xff; (p)[3] = (v >> 24) & 0xff; }
49#define U8TO32_LITTLE(p)   \
50	(((u32)((p)[0])      ) | ((u32)((p)[1]) <<  8) | \
51	 ((u32)((p)[2]) << 16) | ((u32)((p)[3]) << 24)   )
52
53struct salsa20_ctx
54{
55	u32 input[16];
56};
57
58static void salsa20_wordtobyte(u8 output[64], const u32 input[16])
59{
60	u32 x[16];
61	int i;
62
63	memcpy(x, input, sizeof(x));
64	for (i = 20; i > 0; i -= 2) {
65		x[ 4] ^= rol32((x[ 0] + x[12]),  7);
66		x[ 8] ^= rol32((x[ 4] + x[ 0]),  9);
67		x[12] ^= rol32((x[ 8] + x[ 4]), 13);
68		x[ 0] ^= rol32((x[12] + x[ 8]), 18);
69		x[ 9] ^= rol32((x[ 5] + x[ 1]),  7);
70		x[13] ^= rol32((x[ 9] + x[ 5]),  9);
71		x[ 1] ^= rol32((x[13] + x[ 9]), 13);
72		x[ 5] ^= rol32((x[ 1] + x[13]), 18);
73		x[14] ^= rol32((x[10] + x[ 6]),  7);
74		x[ 2] ^= rol32((x[14] + x[10]),  9);
75		x[ 6] ^= rol32((x[ 2] + x[14]), 13);
76		x[10] ^= rol32((x[ 6] + x[ 2]), 18);
77		x[ 3] ^= rol32((x[15] + x[11]),  7);
78		x[ 7] ^= rol32((x[ 3] + x[15]),  9);
79		x[11] ^= rol32((x[ 7] + x[ 3]), 13);
80		x[15] ^= rol32((x[11] + x[ 7]), 18);
81		x[ 1] ^= rol32((x[ 0] + x[ 3]),  7);
82		x[ 2] ^= rol32((x[ 1] + x[ 0]),  9);
83		x[ 3] ^= rol32((x[ 2] + x[ 1]), 13);
84		x[ 0] ^= rol32((x[ 3] + x[ 2]), 18);
85		x[ 6] ^= rol32((x[ 5] + x[ 4]),  7);
86		x[ 7] ^= rol32((x[ 6] + x[ 5]),  9);
87		x[ 4] ^= rol32((x[ 7] + x[ 6]), 13);
88		x[ 5] ^= rol32((x[ 4] + x[ 7]), 18);
89		x[11] ^= rol32((x[10] + x[ 9]),  7);
90		x[ 8] ^= rol32((x[11] + x[10]),  9);
91		x[ 9] ^= rol32((x[ 8] + x[11]), 13);
92		x[10] ^= rol32((x[ 9] + x[ 8]), 18);
93		x[12] ^= rol32((x[15] + x[14]),  7);
94		x[13] ^= rol32((x[12] + x[15]),  9);
95		x[14] ^= rol32((x[13] + x[12]), 13);
96		x[15] ^= rol32((x[14] + x[13]), 18);
97	}
98	for (i = 0; i < 16; ++i)
99		x[i] += input[i];
100	for (i = 0; i < 16; ++i)
101		U32TO8_LITTLE(output + 4 * i,x[i]);
102}
103
104static const char sigma[16] = "expand 32-byte k";
105static const char tau[16] = "expand 16-byte k";
106
107static void salsa20_keysetup(struct salsa20_ctx *ctx, const u8 *k, u32 kbytes)
108{
109	const char *constants;
110
111	ctx->input[1] = U8TO32_LITTLE(k + 0);
112	ctx->input[2] = U8TO32_LITTLE(k + 4);
113	ctx->input[3] = U8TO32_LITTLE(k + 8);
114	ctx->input[4] = U8TO32_LITTLE(k + 12);
115	if (kbytes == 32) { /* recommended */
116		k += 16;
117		constants = sigma;
118	} else { /* kbytes == 16 */
119		constants = tau;
120	}
121	ctx->input[11] = U8TO32_LITTLE(k + 0);
122	ctx->input[12] = U8TO32_LITTLE(k + 4);
123	ctx->input[13] = U8TO32_LITTLE(k + 8);
124	ctx->input[14] = U8TO32_LITTLE(k + 12);
125	ctx->input[0] = U8TO32_LITTLE(constants + 0);
126	ctx->input[5] = U8TO32_LITTLE(constants + 4);
127	ctx->input[10] = U8TO32_LITTLE(constants + 8);
128	ctx->input[15] = U8TO32_LITTLE(constants + 12);
129}
130
131static void salsa20_ivsetup(struct salsa20_ctx *ctx, const u8 *iv)
132{
133	ctx->input[6] = U8TO32_LITTLE(iv + 0);
134	ctx->input[7] = U8TO32_LITTLE(iv + 4);
135	ctx->input[8] = 0;
136	ctx->input[9] = 0;
137}
138
139static void salsa20_encrypt_bytes(struct salsa20_ctx *ctx, u8 *dst,
140				  const u8 *src, unsigned int bytes)
141{
142	u8 buf[64];
143
144	if (dst != src)
145		memcpy(dst, src, bytes);
146
147	while (bytes) {
148		salsa20_wordtobyte(buf, ctx->input);
149
150		ctx->input[8]++;
151		if (!ctx->input[8])
152			ctx->input[9]++;
153
154		if (bytes <= 64) {
155			crypto_xor(dst, buf, bytes);
156			return;
157		}
158
159		crypto_xor(dst, buf, 64);
160		bytes -= 64;
161		dst += 64;
162	}
163}
164
165/*
166 * End of code taken from D. J. Bernstein's reference implementation.
167 */
168
169static int setkey(struct crypto_tfm *tfm, const u8 *key,
170		  unsigned int keysize)
171{
172	struct salsa20_ctx *ctx = crypto_tfm_ctx(tfm);
173	salsa20_keysetup(ctx, key, keysize);
174	return 0;
175}
176
177static int encrypt(struct blkcipher_desc *desc,
178		   struct scatterlist *dst, struct scatterlist *src,
179		   unsigned int nbytes)
180{
181	struct blkcipher_walk walk;
182	struct crypto_blkcipher *tfm = desc->tfm;
183	struct salsa20_ctx *ctx = crypto_blkcipher_ctx(tfm);
184	int err;
185
186	blkcipher_walk_init(&walk, dst, src, nbytes);
187	err = blkcipher_walk_virt_block(desc, &walk, 64);
188
189	salsa20_ivsetup(ctx, walk.iv);
190
191	if (likely(walk.nbytes == nbytes))
192	{
193		salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,
194				      walk.src.virt.addr, nbytes);
195		return blkcipher_walk_done(desc, &walk, 0);
196	}
197
198	while (walk.nbytes >= 64) {
199		salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,
200				      walk.src.virt.addr,
201				      walk.nbytes - (walk.nbytes % 64));
202		err = blkcipher_walk_done(desc, &walk, walk.nbytes % 64);
203	}
204
205	if (walk.nbytes) {
206		salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,
207				      walk.src.virt.addr, walk.nbytes);
208		err = blkcipher_walk_done(desc, &walk, 0);
209	}
210
211	return err;
212}
213
214static struct crypto_alg alg = {
215	.cra_name           =   "salsa20",
216	.cra_driver_name    =   "salsa20-generic",
217	.cra_priority       =   100,
218	.cra_flags          =   CRYPTO_ALG_TYPE_BLKCIPHER,
219	.cra_type           =   &crypto_blkcipher_type,
220	.cra_blocksize      =   1,
221	.cra_ctxsize        =   sizeof(struct salsa20_ctx),
222	.cra_alignmask      =	3,
223	.cra_module         =   THIS_MODULE,
224	.cra_u              =   {
225		.blkcipher = {
226			.setkey         =   setkey,
227			.encrypt        =   encrypt,
228			.decrypt        =   encrypt,
229			.min_keysize    =   SALSA20_MIN_KEY_SIZE,
230			.max_keysize    =   SALSA20_MAX_KEY_SIZE,
231			.ivsize         =   SALSA20_IV_SIZE,
232		}
233	}
234};
235
236static int __init salsa20_generic_mod_init(void)
237{
238	return crypto_register_alg(&alg);
239}
240
241static void __exit salsa20_generic_mod_fini(void)
242{
243	crypto_unregister_alg(&alg);
244}
245
246module_init(salsa20_generic_mod_init);
247module_exit(salsa20_generic_mod_fini);
248
249MODULE_LICENSE("GPL");
250MODULE_DESCRIPTION ("Salsa20 stream cipher algorithm");
251MODULE_ALIAS("salsa20");
252