LXR linux/crypto/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/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