aboutsummaryrefslogtreecommitdiff
path: root/crypto/salsa20_generic.c
blob: 8c77bc78a09f2693a1b8acf4e8748d10ced93da7 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
/*
 * 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 <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)];

	if (dst != src)
		memcpy(dst, src, bytes);

	while (bytes >= SALSA20_BLOCK_SIZE) {
		salsa20_block(state, stream);
		crypto_xor(dst, (const u8 *)stream, SALSA20_BLOCK_SIZE);
		bytes -= SALSA20_BLOCK_SIZE;
		dst += SALSA20_BLOCK_SIZE;
	}
	if (bytes) {
		salsa20_block(state, stream);
		crypto_xor(dst, (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, true);

	salsa20_init(state, ctx, walk.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);
}

module_init(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");