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 "��-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
46static 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
55static 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
78static 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
115static 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
131static 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
143static 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
150static 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
168static int __init ghash_mod_init(void)
169{
170	return crypto_register_shash(&ghash_alg);
171}
172
173static void __exit ghash_mod_exit(void)
174{
175	crypto_unregister_shash(&ghash_alg);
176}
177
178subsys_initcall(ghash_mod_init);
179module_exit(ghash_mod_exit);
180
181MODULE_LICENSE("GPL");
182MODULE_DESCRIPTION("GHASH hash function");
183MODULE_ALIAS_CRYPTO("ghash");
184MODULE_ALIAS_CRYPTO("ghash-generic");
185