xref: /openbmc/linux/crypto/polyval-generic.c (revision 34f7f6c3)
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 
57 struct polyval_tfm_ctx {
58 	struct gf128mul_4k *gf128;
59 };
60 
61 struct polyval_desc_ctx {
62 	union {
63 		u8 buffer[POLYVAL_BLOCK_SIZE];
64 		be128 buffer128;
65 	};
66 	u32 bytes;
67 };
68 
copy_and_reverse(u8 dst[POLYVAL_BLOCK_SIZE],const u8 src[POLYVAL_BLOCK_SIZE])69 static 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  */
polyval_mul_non4k(u8 * op1,const u8 * op2)87 void 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 }
98 EXPORT_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  */
polyval_update_non4k(const u8 * key,const u8 * in,size_t nblocks,u8 * accumulator)108 void 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 }
117 EXPORT_SYMBOL_GPL(polyval_update_non4k);
118 
polyval_setkey(struct crypto_shash * tfm,const u8 * key,unsigned int keylen)119 static 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 
polyval_init(struct shash_desc * desc)143 static 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 
polyval_update(struct shash_desc * desc,const u8 * src,unsigned int srclen)152 static 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 
polyval_final(struct shash_desc * desc,u8 * dst)193 static 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 
polyval_exit_tfm(struct crypto_tfm * tfm)204 static 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 
211 static 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 
polyval_mod_init(void)229 static int __init polyval_mod_init(void)
230 {
231 	return crypto_register_shash(&polyval_alg);
232 }
233 
polyval_mod_exit(void)234 static void __exit polyval_mod_exit(void)
235 {
236 	crypto_unregister_shash(&polyval_alg);
237 }
238 
239 subsys_initcall(polyval_mod_init);
240 module_exit(polyval_mod_exit);
241 
242 MODULE_LICENSE("GPL");
243 MODULE_DESCRIPTION("POLYVAL hash function");
244 MODULE_ALIAS_CRYPTO("polyval");
245 MODULE_ALIAS_CRYPTO("polyval-generic");
246