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 
ghash_init(struct shash_desc * desc)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 
ghash_setkey(struct crypto_shash * tfm,const u8 * key,unsigned int keylen)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 
ghash_update(struct shash_desc * desc,const u8 * src,unsigned int srclen)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 
ghash_flush(struct ghash_ctx * ctx,struct ghash_desc_ctx * dctx)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 
ghash_final(struct shash_desc * desc,u8 * dst)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 
ghash_exit_tfm(struct crypto_tfm * tfm)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 
ghash_mod_init(void)168 static int __init ghash_mod_init(void)
169 {
170 	return crypto_register_shash(&ghash_alg);
171 }
172 
ghash_mod_exit(void)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");
185