linux/crypto/ghash-generic.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * GHASH: hash function for GCM (Galois/Counter Mode).
 *
 * Copyright (c) 2007 Nokia Siemens Networks - Mikko Herranen <[email protected]>
 * Copyright (c) 2009 Intel Corp.
 *   Author: Huang Ying <[email protected]>
 */

/*
 * GHASH is a keyed hash function used in GCM authentication tag generation.
 *
 * The original GCM paper [1] presents GHASH as a function GHASH(H, A, C) which
 * takes a 16-byte hash key H, additional authenticated data A, and a ciphertext
 * C.  It formats A and C into a single byte string X, interprets X as a
 * polynomial over GF(2^128), and evaluates this polynomial at the point H.
 *
 * However, the NIST standard for GCM [2] presents GHASH as GHASH(H, X) where X
 * is the already-formatted byte string containing both A and C.
 *
 * "ghash" in the Linux crypto API uses the 'X' (pre-formatted) convention,
 * since the API supports only a single data stream per hash.  Thus, the
 * formatting of 'A' and 'C' is done in the "gcm" template, not in "ghash".
 *
 * The reason "ghash" is separate from "gcm" is to allow "gcm" to use an
 * accelerated "ghash" when a standalone accelerated "gcm(aes)" is unavailable.
 * It is generally inappropriate to use "ghash" for other purposes, since it is
 * an "ε-almost-XOR-universal hash function", not a cryptographic hash function.
 * It can only be used securely in crypto modes specially designed to use it.
 *
 * [1] The Galois/Counter Mode of Operation (GCM)
 *     (http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.694.695&rep=rep1&type=pdf)
 * [2] Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC
 *     (https://csrc.nist.gov/publications/detail/sp/800-38d/final)
 */

#include <crypto/algapi.h>
#include <crypto/gf128mul.h>
#include <crypto/ghash.h>
#include <crypto/internal/hash.h>
#include <linux/crypto.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>

static int ghash_init(struct shash_desc *desc)
{ … }

static int ghash_setkey(struct crypto_shash *tfm,
			const u8 *key, unsigned int keylen)
{ … }

static int ghash_update(struct shash_desc *desc,
			 const u8 *src, unsigned int srclen)
{ … }

static void ghash_flush(struct ghash_ctx *ctx, struct ghash_desc_ctx *dctx)
{ … }

static int ghash_final(struct shash_desc *desc, u8 *dst)
{ … }

static void ghash_exit_tfm(struct crypto_tfm *tfm)
{ … }

static struct shash_alg ghash_alg = …;

static int __init ghash_mod_init(void)
{ … }

static void __exit ghash_mod_exit(void)
{ … }

subsys_initcall(ghash_mod_init);
module_exit(ghash_mod_exit);

MODULE_LICENSE(…) …;
MODULE_DESCRIPTION(…) …;
MODULE_ALIAS_CRYPTO(…) …;
MODULE_ALIAS_CRYPTO(…) …;