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 | |
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 | */ |
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(dst: (u8 *)&a, src: op1); |
93 | copy_and_reverse(dst: (u8 *)&b, src: op2); |
94 | gf128mul_x_lle(r: &a, x: &a); |
95 | gf128mul_lle(a: &a, b: &b); |
96 | copy_and_reverse(dst: op1, src: (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 | */ |
108 | void polyval_update_non4k(const u8 *key, const u8 *in, |
109 | size_t nblocks, u8 *accumulator) |
110 | { |
111 | while (nblocks--) { |
112 | crypto_xor(dst: accumulator, src: 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 | |
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(t: ctx->gf128); |
129 | |
130 | BUILD_BUG_ON(sizeof(k) != POLYVAL_BLOCK_SIZE); |
131 | copy_and_reverse(dst: (u8 *)&k, src: key); |
132 | gf128mul_x_lle(r: &k, x: &k); |
133 | |
134 | ctx->gf128 = gf128mul_init_4k_lle(g: &k); |
135 | memzero_explicit(s: &k, POLYVAL_BLOCK_SIZE); |
136 | |
137 | if (!ctx->gf128) |
138 | return -ENOMEM; |
139 | |
140 | return 0; |
141 | } |
142 | |
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 | |
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(tfm: 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(a: &dctx->buffer128, t: ctx->gf128); |
173 | } |
174 | |
175 | while (srclen >= POLYVAL_BLOCK_SIZE) { |
176 | copy_and_reverse(dst: tmp, src); |
177 | crypto_xor(dst: dctx->buffer, src: tmp, POLYVAL_BLOCK_SIZE); |
178 | gf128mul_4k_lle(a: &dctx->buffer128, t: 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 | |
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(tfm: desc->tfm); |
197 | |
198 | if (dctx->bytes) |
199 | gf128mul_4k_lle(a: &dctx->buffer128, t: ctx->gf128); |
200 | copy_and_reverse(dst, src: dctx->buffer); |
201 | return 0; |
202 | } |
203 | |
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(t: 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 | |
229 | static int __init polyval_mod_init(void) |
230 | { |
231 | return crypto_register_shash(alg: &polyval_alg); |
232 | } |
233 | |
234 | static void __exit polyval_mod_exit(void) |
235 | { |
236 | crypto_unregister_shash(alg: &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 | |