1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * POLYVAL: hash function for HCTR2.
4 *
5 * Copyright (c) 2007 Nokia Siemens Networks - Mikko Herranen <mh1@iki.fi>
6 * Copyright (c) 2009 Intel Corp.
7 *   Author: Huang Ying <ying.huang@intel.com>
8 * Copyright 2021 Google LLC
9 */
10
11/*
12 * Code based on crypto/ghash-generic.c
13 *
14 * POLYVAL is a keyed hash function similar to GHASH. POLYVAL uses a different
15 * modulus for finite field multiplication which makes hardware accelerated
16 * implementations on little-endian machines faster. POLYVAL is used in the
17 * kernel to implement HCTR2, but was originally specified for AES-GCM-SIV
18 * (RFC 8452).
19 *
20 * For more information see:
21 * Length-preserving encryption with HCTR2:
22 *   https://eprint.iacr.org/2021/1441.pdf
23 * AES-GCM-SIV: Nonce Misuse-Resistant Authenticated Encryption:
24 *   https://datatracker.ietf.org/doc/html/rfc8452
25 *
26 * Like GHASH, POLYVAL is not a cryptographic hash function and should
27 * not be used outside of crypto modes explicitly designed to use POLYVAL.
28 *
29 * This implementation uses a convenient trick involving the GHASH and POLYVAL
30 * fields. This trick allows multiplication in the POLYVAL field to be
31 * implemented by using multiplication in the GHASH field as a subroutine. An
32 * element of the POLYVAL field can be converted to an element of the GHASH
33 * field by computing x*REVERSE(a), where REVERSE reverses the byte-ordering of
34 * a. Similarly, an element of the GHASH field can be converted back to the
35 * POLYVAL field by computing REVERSE(x^{-1}*a). For more information, see:
36 * https://datatracker.ietf.org/doc/html/rfc8452#appendix-A
37 *
38 * By using this trick, we do not need to implement the POLYVAL field for the
39 * generic implementation.
40 *
41 * Warning: this generic implementation is not intended to be used in practice
42 * and is not constant time. For practical use, a hardware accelerated
43 * implementation of POLYVAL should be used instead.
44 *
45 */
46
47#include <asm/unaligned.h>
48#include <crypto/algapi.h>
49#include <crypto/gf128mul.h>
50#include <crypto/polyval.h>
51#include <crypto/internal/hash.h>
52#include <linux/crypto.h>
53#include <linux/init.h>
54#include <linux/kernel.h>
55#include <linux/module.h>
56
57struct polyval_tfm_ctx {
58	struct gf128mul_4k *gf128;
59};
60
61struct polyval_desc_ctx {
62	union {
63		u8 buffer[POLYVAL_BLOCK_SIZE];
64		be128 buffer128;
65	};
66	u32 bytes;
67};
68
69static void copy_and_reverse(u8 dst[POLYVAL_BLOCK_SIZE],
70			     const u8 src[POLYVAL_BLOCK_SIZE])
71{
72	u64 a = get_unaligned((const u64 *)&src[0]);
73	u64 b = get_unaligned((const u64 *)&src[8]);
74
75	put_unaligned(swab64(a), (u64 *)&dst[8]);
76	put_unaligned(swab64(b), (u64 *)&dst[0]);
77}
78
79/*
80 * Performs multiplication in the POLYVAL field using the GHASH field as a
81 * subroutine.  This function is used as a fallback for hardware accelerated
82 * implementations when simd registers are unavailable.
83 *
84 * Note: This function is not used for polyval-generic, instead we use the 4k
85 * lookup table implementation for finite field multiplication.
86 */
87void polyval_mul_non4k(u8 *op1, const u8 *op2)
88{
89	be128 a, b;
90
91	// Assume one argument is in Montgomery form and one is not.
92	copy_and_reverse((u8 *)&a, op1);
93	copy_and_reverse((u8 *)&b, op2);
94	gf128mul_x_lle(&a, &a);
95	gf128mul_lle(&a, &b);
96	copy_and_reverse(op1, (u8 *)&a);
97}
98EXPORT_SYMBOL_GPL(polyval_mul_non4k);
99
100/*
101 * Perform a POLYVAL update using non4k multiplication.  This function is used
102 * as a fallback for hardware accelerated implementations when simd registers
103 * are unavailable.
104 *
105 * Note: This function is not used for polyval-generic, instead we use the 4k
106 * lookup table implementation of finite field multiplication.
107 */
108void polyval_update_non4k(const u8 *key, const u8 *in,
109			  size_t nblocks, u8 *accumulator)
110{
111	while (nblocks--) {
112		crypto_xor(accumulator, in, POLYVAL_BLOCK_SIZE);
113		polyval_mul_non4k(accumulator, key);
114		in += POLYVAL_BLOCK_SIZE;
115	}
116}
117EXPORT_SYMBOL_GPL(polyval_update_non4k);
118
119static int polyval_setkey(struct crypto_shash *tfm,
120			  const u8 *key, unsigned int keylen)
121{
122	struct polyval_tfm_ctx *ctx = crypto_shash_ctx(tfm);
123	be128 k;
124
125	if (keylen != POLYVAL_BLOCK_SIZE)
126		return -EINVAL;
127
128	gf128mul_free_4k(ctx->gf128);
129
130	BUILD_BUG_ON(sizeof(k) != POLYVAL_BLOCK_SIZE);
131	copy_and_reverse((u8 *)&k, key);
132	gf128mul_x_lle(&k, &k);
133
134	ctx->gf128 = gf128mul_init_4k_lle(&k);
135	memzero_explicit(&k, POLYVAL_BLOCK_SIZE);
136
137	if (!ctx->gf128)
138		return -ENOMEM;
139
140	return 0;
141}
142
143static int polyval_init(struct shash_desc *desc)
144{
145	struct polyval_desc_ctx *dctx = shash_desc_ctx(desc);
146
147	memset(dctx, 0, sizeof(*dctx));
148
149	return 0;
150}
151
152static int polyval_update(struct shash_desc *desc,
153			 const u8 *src, unsigned int srclen)
154{
155	struct polyval_desc_ctx *dctx = shash_desc_ctx(desc);
156	const struct polyval_tfm_ctx *ctx = crypto_shash_ctx(desc->tfm);
157	u8 *pos;
158	u8 tmp[POLYVAL_BLOCK_SIZE];
159	int n;
160
161	if (dctx->bytes) {
162		n = min(srclen, dctx->bytes);
163		pos = dctx->buffer + dctx->bytes - 1;
164
165		dctx->bytes -= n;
166		srclen -= n;
167
168		while (n--)
169			*pos-- ^= *src++;
170
171		if (!dctx->bytes)
172			gf128mul_4k_lle(&dctx->buffer128, ctx->gf128);
173	}
174
175	while (srclen >= POLYVAL_BLOCK_SIZE) {
176		copy_and_reverse(tmp, src);
177		crypto_xor(dctx->buffer, tmp, POLYVAL_BLOCK_SIZE);
178		gf128mul_4k_lle(&dctx->buffer128, ctx->gf128);
179		src += POLYVAL_BLOCK_SIZE;
180		srclen -= POLYVAL_BLOCK_SIZE;
181	}
182
183	if (srclen) {
184		dctx->bytes = POLYVAL_BLOCK_SIZE - srclen;
185		pos = dctx->buffer + POLYVAL_BLOCK_SIZE - 1;
186		while (srclen--)
187			*pos-- ^= *src++;
188	}
189
190	return 0;
191}
192
193static int polyval_final(struct shash_desc *desc, u8 *dst)
194{
195	struct polyval_desc_ctx *dctx = shash_desc_ctx(desc);
196	const struct polyval_tfm_ctx *ctx = crypto_shash_ctx(desc->tfm);
197
198	if (dctx->bytes)
199		gf128mul_4k_lle(&dctx->buffer128, ctx->gf128);
200	copy_and_reverse(dst, dctx->buffer);
201	return 0;
202}
203
204static void polyval_exit_tfm(struct crypto_tfm *tfm)
205{
206	struct polyval_tfm_ctx *ctx = crypto_tfm_ctx(tfm);
207
208	gf128mul_free_4k(ctx->gf128);
209}
210
211static struct shash_alg polyval_alg = {
212	.digestsize	= POLYVAL_DIGEST_SIZE,
213	.init		= polyval_init,
214	.update		= polyval_update,
215	.final		= polyval_final,
216	.setkey		= polyval_setkey,
217	.descsize	= sizeof(struct polyval_desc_ctx),
218	.base		= {
219		.cra_name		= "polyval",
220		.cra_driver_name	= "polyval-generic",
221		.cra_priority		= 100,
222		.cra_blocksize		= POLYVAL_BLOCK_SIZE,
223		.cra_ctxsize		= sizeof(struct polyval_tfm_ctx),
224		.cra_module		= THIS_MODULE,
225		.cra_exit		= polyval_exit_tfm,
226	},
227};
228
229static int __init polyval_mod_init(void)
230{
231	return crypto_register_shash(&polyval_alg);
232}
233
234static void __exit polyval_mod_exit(void)
235{
236	crypto_unregister_shash(&polyval_alg);
237}
238
239subsys_initcall(polyval_mod_init);
240module_exit(polyval_mod_exit);
241
242MODULE_LICENSE("GPL");
243MODULE_DESCRIPTION("POLYVAL hash function");
244MODULE_ALIAS_CRYPTO("polyval");
245MODULE_ALIAS_CRYPTO("polyval-generic");
246