linux/crypto/ghash-generic.c

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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;
crypto: remove CRYPTO_TFM_RES_BAD_KEY_LEN The CRYPTO_TFM_RES_BAD_KEY_LEN flag was apparently meant as a way to make the ->setkey() functions provide more information about errors. However, no one actually checks for this flag, which makes it pointless. Also, many algorithms fail to set this flag when given a bad length key. Reviewing just the generic implementations, this is the case for aes-fixed-time, cbcmac, echainiv, nhpoly1305, pcrypt, rfc3686, rfc4309, rfc7539, rfc7539esp, salsa20, seqiv, and xcbc. But there are probably many more in arch/*/crypto/ and drivers/crypto/. Some algorithms can even set this flag when the key is the correct length. For example, authenc and authencesn set it when the key payload is malformed in any way (not just a bad length), the atmel-sha and ccree drivers can set it if a memory allocation fails, and the chelsio driver sets it for bad auth tag lengths, not just bad key lengths. So even if someone actually wanted to start checking this flag (which seems unlikely, since it's been unused for a long time), there would be a lot of work needed to get it working correctly. But it would probably be much better to go back to the drawing board and just define different return values, like -EINVAL if the key is invalid for the algorithm vs. -EKEYREJECTED if the key was rejected by a policy like "no weak keys". That would be much simpler, less error-prone, and easier to test. So just remove this flag. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Horia Geantă <horia.geanta@nxp.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2019-12-31 03:19:36 +00:00
if (keylen != GHASH_BLOCK_SIZE)
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");