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1 | // SPDX-License-Identifier: GPL-2.0-only | |
2 | /* | |
3 | * GHASH: hash function for GCM (Galois/Counter Mode). | |
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 | */ | |
9 | ||
10 | /* | |
11 | * GHASH is a keyed hash function used in GCM authentication tag generation. | |
12 | * | |
13 | * The original GCM paper [1] presents GHASH as a function GHASH(H, A, C) which | |
14 | * takes a 16-byte hash key H, additional authenticated data A, and a ciphertext | |
15 | * C. It formats A and C into a single byte string X, interprets X as a | |
16 | * polynomial over GF(2^128), and evaluates this polynomial at the point H. | |
17 | * | |
18 | * However, the NIST standard for GCM [2] presents GHASH as GHASH(H, X) where X | |
19 | * is the already-formatted byte string containing both A and C. | |
20 | * | |
21 | * "ghash" in the Linux crypto API uses the 'X' (pre-formatted) convention, | |
22 | * since the API supports only a single data stream per hash. Thus, the | |
23 | * formatting of 'A' and 'C' is done in the "gcm" template, not in "ghash". | |
24 | * | |
25 | * The reason "ghash" is separate from "gcm" is to allow "gcm" to use an | |
26 | * accelerated "ghash" when a standalone accelerated "gcm(aes)" is unavailable. | |
27 | * It is generally inappropriate to use "ghash" for other purposes, since it is | |
28 | * an "ε-almost-XOR-universal hash function", not a cryptographic hash function. | |
29 | * It can only be used securely in crypto modes specially designed to use it. | |
30 | * | |
31 | * [1] The Galois/Counter Mode of Operation (GCM) | |
32 | * (http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.694.695&rep=rep1&type=pdf) | |
33 | * [2] Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC | |
34 | * (https://csrc.nist.gov/publications/detail/sp/800-38d/final) | |
35 | */ | |
36 | ||
37 | #include <crypto/algapi.h> | |
38 | #include <crypto/gf128mul.h> | |
39 | #include <crypto/ghash.h> | |
40 | #include <crypto/internal/hash.h> | |
41 | #include <linux/crypto.h> | |
42 | #include <linux/init.h> | |
43 | #include <linux/kernel.h> | |
44 | #include <linux/module.h> | |
45 | ||
46 | static int ghash_init(struct shash_desc *desc) | |
47 | { | |
48 | struct ghash_desc_ctx *dctx = shash_desc_ctx(desc); | |
49 | ||
50 | memset(dctx, 0, sizeof(*dctx)); | |
51 | ||
52 | return 0; | |
53 | } | |
54 | ||
55 | static int ghash_setkey(struct crypto_shash *tfm, | |
56 | const u8 *key, unsigned int keylen) | |
57 | { | |
58 | struct ghash_ctx *ctx = crypto_shash_ctx(tfm); | |
59 | be128 k; | |
60 | ||
61 | if (keylen != GHASH_BLOCK_SIZE) | |
62 | return -EINVAL; | |
63 | ||
64 | if (ctx->gf128) | |
65 | gf128mul_free_4k(ctx->gf128); | |
66 | ||
67 | BUILD_BUG_ON(sizeof(k) != GHASH_BLOCK_SIZE); | |
68 | memcpy(&k, key, GHASH_BLOCK_SIZE); /* avoid violating alignment rules */ | |
69 | ctx->gf128 = gf128mul_init_4k_lle(&k); | |
70 | memzero_explicit(&k, GHASH_BLOCK_SIZE); | |
71 | ||
72 | if (!ctx->gf128) | |
73 | return -ENOMEM; | |
74 | ||
75 | return 0; | |
76 | } | |
77 | ||
78 | static int ghash_update(struct shash_desc *desc, | |
79 | const u8 *src, unsigned int srclen) | |
80 | { | |
81 | struct ghash_desc_ctx *dctx = shash_desc_ctx(desc); | |
82 | struct ghash_ctx *ctx = crypto_shash_ctx(desc->tfm); | |
83 | u8 *dst = dctx->buffer; | |
84 | ||
85 | if (dctx->bytes) { | |
86 | int n = min(srclen, dctx->bytes); | |
87 | u8 *pos = dst + (GHASH_BLOCK_SIZE - dctx->bytes); | |
88 | ||
89 | dctx->bytes -= n; | |
90 | srclen -= n; | |
91 | ||
92 | while (n--) | |
93 | *pos++ ^= *src++; | |
94 | ||
95 | if (!dctx->bytes) | |
96 | gf128mul_4k_lle((be128 *)dst, ctx->gf128); | |
97 | } | |
98 | ||
99 | while (srclen >= GHASH_BLOCK_SIZE) { | |
100 | crypto_xor(dst, src, GHASH_BLOCK_SIZE); | |
101 | gf128mul_4k_lle((be128 *)dst, ctx->gf128); | |
102 | src += GHASH_BLOCK_SIZE; | |
103 | srclen -= GHASH_BLOCK_SIZE; | |
104 | } | |
105 | ||
106 | if (srclen) { | |
107 | dctx->bytes = GHASH_BLOCK_SIZE - srclen; | |
108 | while (srclen--) | |
109 | *dst++ ^= *src++; | |
110 | } | |
111 | ||
112 | return 0; | |
113 | } | |
114 | ||
115 | static void ghash_flush(struct ghash_ctx *ctx, struct ghash_desc_ctx *dctx) | |
116 | { | |
117 | u8 *dst = dctx->buffer; | |
118 | ||
119 | if (dctx->bytes) { | |
120 | u8 *tmp = dst + (GHASH_BLOCK_SIZE - dctx->bytes); | |
121 | ||
122 | while (dctx->bytes--) | |
123 | *tmp++ ^= 0; | |
124 | ||
125 | gf128mul_4k_lle((be128 *)dst, ctx->gf128); | |
126 | } | |
127 | ||
128 | dctx->bytes = 0; | |
129 | } | |
130 | ||
131 | static int ghash_final(struct shash_desc *desc, u8 *dst) | |
132 | { | |
133 | struct ghash_desc_ctx *dctx = shash_desc_ctx(desc); | |
134 | struct ghash_ctx *ctx = crypto_shash_ctx(desc->tfm); | |
135 | u8 *buf = dctx->buffer; | |
136 | ||
137 | ghash_flush(ctx, dctx); | |
138 | memcpy(dst, buf, GHASH_BLOCK_SIZE); | |
139 | ||
140 | return 0; | |
141 | } | |
142 | ||
143 | static void ghash_exit_tfm(struct crypto_tfm *tfm) | |
144 | { | |
145 | struct ghash_ctx *ctx = crypto_tfm_ctx(tfm); | |
146 | if (ctx->gf128) | |
147 | gf128mul_free_4k(ctx->gf128); | |
148 | } | |
149 | ||
150 | static struct shash_alg ghash_alg = { | |
151 | .digestsize = GHASH_DIGEST_SIZE, | |
152 | .init = ghash_init, | |
153 | .update = ghash_update, | |
154 | .final = ghash_final, | |
155 | .setkey = ghash_setkey, | |
156 | .descsize = sizeof(struct ghash_desc_ctx), | |
157 | .base = { | |
158 | .cra_name = "ghash", | |
159 | .cra_driver_name = "ghash-generic", | |
160 | .cra_priority = 100, | |
161 | .cra_blocksize = GHASH_BLOCK_SIZE, | |
162 | .cra_ctxsize = sizeof(struct ghash_ctx), | |
163 | .cra_module = THIS_MODULE, | |
164 | .cra_exit = ghash_exit_tfm, | |
165 | }, | |
166 | }; | |
167 | ||
168 | static int __init ghash_mod_init(void) | |
169 | { | |
170 | return crypto_register_shash(&ghash_alg); | |
171 | } | |
172 | ||
173 | static void __exit ghash_mod_exit(void) | |
174 | { | |
175 | crypto_unregister_shash(&ghash_alg); | |
176 | } | |
177 | ||
178 | subsys_initcall(ghash_mod_init); | |
179 | module_exit(ghash_mod_exit); | |
180 | ||
181 | MODULE_LICENSE("GPL"); | |
182 | MODULE_DESCRIPTION("GHASH hash function"); | |
183 | MODULE_ALIAS_CRYPTO("ghash"); | |
184 | MODULE_ALIAS_CRYPTO("ghash-generic"); |