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
  46 static 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
  55 static 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
  78 static 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
 115 static 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
 131 static 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
 143 static 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
 150 static 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
 168 static int __init ghash_mod_init(void)
 169 {
 170         return crypto_register_shash(&ghash_alg);
 171 }
 172
 173 static void __exit ghash_mod_exit(void)
 174 {
 175         crypto_unregister_shash(&ghash_alg);
 176 }
 177
 178 subsys_initcall(ghash_mod_init);
 179 module_exit(ghash_mod_exit);
 180
 181 MODULE_LICENSE("GPL");
 182 MODULE_DESCRIPTION("GHASH hash function");
 183 MODULE_ALIAS_CRYPTO("ghash");
 184 MODULE_ALIAS_CRYPTO("ghash-generic");