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1// SPDX-License-Identifier: GPL-2.0-only2/*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) which14 * takes a 16-byte hash key H, additional authenticated data A, and a ciphertext15 * C. It formats A and C into a single byte string X, interprets X as a16 * 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 X19 * 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, the23 * 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 an26 * accelerated "ghash" when a standalone accelerated "gcm(aes)" is unavailable.27 * It is generally inappropriate to use "ghash" for other purposes, since it is28 * 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 GMAC34 * (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