ghash-generic.c

  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/gf128mul.h>
 38#include <crypto/ghash.h>
 39#include <crypto/internal/hash.h>
 40#include <crypto/utils.h>
 41#include <linux/err.h>
 42#include <linux/kernel.h>
 43#include <linux/module.h>
 44#include <linux/string.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	do {
 86		crypto_xor(dst, src, GHASH_BLOCK_SIZE);
 87		gf128mul_4k_lle((be128 *)dst, ctx->gf128);
 88		src += GHASH_BLOCK_SIZE;
 89		srclen -= GHASH_BLOCK_SIZE;
 90	} while (srclen >= GHASH_BLOCK_SIZE);
 91
 92	return srclen;
 93}
 94
 95static void ghash_flush(struct shash_desc *desc, const u8 *src,
 96			unsigned int len)
 97{
 98	struct ghash_ctx *ctx = crypto_shash_ctx(desc->tfm);
 99	struct ghash_desc_ctx *dctx = shash_desc_ctx(desc);
100	u8 *dst = dctx->buffer;
101
102	if (len) {
103		crypto_xor(dst, src, len);
104		gf128mul_4k_lle((be128 *)dst, ctx->gf128);
105	}
106}
107
108static int ghash_finup(struct shash_desc *desc, const u8 *src,
109		       unsigned int len, u8 *dst)
110{
111	struct ghash_desc_ctx *dctx = shash_desc_ctx(desc);
112	u8 *buf = dctx->buffer;
113
114	ghash_flush(desc, src, len);
115	memcpy(dst, buf, GHASH_BLOCK_SIZE);
116
117	return 0;
118}
119
120static void ghash_exit_tfm(struct crypto_tfm *tfm)
121{
122	struct ghash_ctx *ctx = crypto_tfm_ctx(tfm);
123	if (ctx->gf128)
124		gf128mul_free_4k(ctx->gf128);
125}
126
127static struct shash_alg ghash_alg = {
128	.digestsize	= GHASH_DIGEST_SIZE,
129	.init		= ghash_init,
130	.update		= ghash_update,
131	.finup		= ghash_finup,
132	.setkey		= ghash_setkey,
133	.descsize	= sizeof(struct ghash_desc_ctx),
134	.base		= {
135		.cra_name		= "ghash",
136		.cra_driver_name	= "ghash-generic",
137		.cra_priority		= 100,
138		.cra_flags		= CRYPTO_AHASH_ALG_BLOCK_ONLY,
139		.cra_blocksize		= GHASH_BLOCK_SIZE,
140		.cra_ctxsize		= sizeof(struct ghash_ctx),
141		.cra_module		= THIS_MODULE,
142		.cra_exit		= ghash_exit_tfm,
143	},
144};
145
146static int __init ghash_mod_init(void)
147{
148	return crypto_register_shash(&ghash_alg);
149}
150
151static void __exit ghash_mod_exit(void)
152{
153	crypto_unregister_shash(&ghash_alg);
154}
155
156module_init(ghash_mod_init);
157module_exit(ghash_mod_exit);
158
159MODULE_LICENSE("GPL");
160MODULE_DESCRIPTION("GHASH hash function");
161MODULE_ALIAS_CRYPTO("ghash");
162MODULE_ALIAS_CRYPTO("ghash-generic");