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// SPDX-License-Identifier: GPL-2.0-only
/*
* GHASH: hash function for GCM (Galois/Counter Mode).
*
* Copyright (c) 2007 Nokia Siemens Networks - Mikko Herranen <mh1@iki.fi>
* Copyright (c) 2009 Intel Corp.
* Author: Huang Ying <ying.huang@intel.com>
*/
/*
* 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)
{
struct ghash_desc_ctx *dctx = shash_desc_ctx(desc);
memset(dctx, 0, sizeof(*dctx));
return 0;
}
static int ghash_setkey(struct crypto_shash *tfm,
const u8 *key, unsigned int keylen)
{
struct ghash_ctx *ctx = crypto_shash_ctx(tfm);
be128 k;
if (keylen != GHASH_BLOCK_SIZE) {
crypto_shash_set_flags(tfm, CRYPTO_TFM_RES_BAD_KEY_LEN);
return -EINVAL;
}
if (ctx->gf128)
gf128mul_free_4k(ctx->gf128);
BUILD_BUG_ON(sizeof(k) != GHASH_BLOCK_SIZE);
memcpy(&k, key, GHASH_BLOCK_SIZE); /* avoid violating alignment rules */
ctx->gf128 = gf128mul_init_4k_lle(&k);
memzero_explicit(&k, GHASH_BLOCK_SIZE);
if (!ctx->gf128)
return -ENOMEM;
return 0;
}
static int ghash_update(struct shash_desc *desc,
const u8 *src, unsigned int srclen)
{
struct ghash_desc_ctx *dctx = shash_desc_ctx(desc);
struct ghash_ctx *ctx = crypto_shash_ctx(desc->tfm);
u8 *dst = dctx->buffer;
if (dctx->bytes) {
int n = min(srclen, dctx->bytes);
u8 *pos = dst + (GHASH_BLOCK_SIZE - dctx->bytes);
dctx->bytes -= n;
srclen -= n;
while (n--)
*pos++ ^= *src++;
if (!dctx->bytes)
gf128mul_4k_lle((be128 *)dst, ctx->gf128);
}
while (srclen >= GHASH_BLOCK_SIZE) {
crypto_xor(dst, src, GHASH_BLOCK_SIZE);
gf128mul_4k_lle((be128 *)dst, ctx->gf128);
src += GHASH_BLOCK_SIZE;
srclen -= GHASH_BLOCK_SIZE;
}
if (srclen) {
dctx->bytes = GHASH_BLOCK_SIZE - srclen;
while (srclen--)
*dst++ ^= *src++;
}
return 0;
}
static void ghash_flush(struct ghash_ctx *ctx, struct ghash_desc_ctx *dctx)
{
u8 *dst = dctx->buffer;
if (dctx->bytes) {
u8 *tmp = dst + (GHASH_BLOCK_SIZE - dctx->bytes);
while (dctx->bytes--)
*tmp++ ^= 0;
gf128mul_4k_lle((be128 *)dst, ctx->gf128);
}
dctx->bytes = 0;
}
static int ghash_final(struct shash_desc *desc, u8 *dst)
{
struct ghash_desc_ctx *dctx = shash_desc_ctx(desc);
struct ghash_ctx *ctx = crypto_shash_ctx(desc->tfm);
u8 *buf = dctx->buffer;
ghash_flush(ctx, dctx);
memcpy(dst, buf, GHASH_BLOCK_SIZE);
return 0;
}
static void ghash_exit_tfm(struct crypto_tfm *tfm)
{
struct ghash_ctx *ctx = crypto_tfm_ctx(tfm);
if (ctx->gf128)
gf128mul_free_4k(ctx->gf128);
}
static struct shash_alg ghash_alg = {
.digestsize = GHASH_DIGEST_SIZE,
.init = ghash_init,
.update = ghash_update,
.final = ghash_final,
.setkey = ghash_setkey,
.descsize = sizeof(struct ghash_desc_ctx),
.base = {
.cra_name = "ghash",
.cra_driver_name = "ghash-generic",
.cra_priority = 100,
.cra_blocksize = GHASH_BLOCK_SIZE,
.cra_ctxsize = sizeof(struct ghash_ctx),
.cra_module = THIS_MODULE,
.cra_exit = ghash_exit_tfm,
},
};
static int __init ghash_mod_init(void)
{
return crypto_register_shash(&ghash_alg);
}
static void __exit ghash_mod_exit(void)
{
crypto_unregister_shash(&ghash_alg);
}
subsys_initcall(ghash_mod_init);
module_exit(ghash_mod_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("GHASH hash function");
MODULE_ALIAS_CRYPTO("ghash");
MODULE_ALIAS_CRYPTO("ghash-generic");
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