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                 crypto_shash_set_flags(tfm, CRYPTO_TFM_RES_BAD_KEY_LEN);
  63                 return -EINVAL;
  64         }
  65
  66         if (ctx->gf128)
  67                 gf128mul_free_4k(ctx->gf128);
  68
  69         BUILD_BUG_ON(sizeof(k) != GHASH_BLOCK_SIZE);
  70         memcpy(&k, key, GHASH_BLOCK_SIZE); /* avoid violating alignment rules */
  71         ctx->gf128 = gf128mul_init_4k_lle(&k);
  72         memzero_explicit(&k, GHASH_BLOCK_SIZE);
  73
  74         if (!ctx->gf128)
  75                 return -ENOMEM;
  76
  77         return 0;
  78 }
  79
  80 static int ghash_update(struct shash_desc *desc,
  81                          const u8 *src, unsigned int srclen)
  82 {
  83         struct ghash_desc_ctx *dctx = shash_desc_ctx(desc);
  84         struct ghash_ctx *ctx = crypto_shash_ctx(desc->tfm);
  85         u8 *dst = dctx->buffer;
  86
  87         if (dctx->bytes) {
  88                 int n = min(srclen, dctx->bytes);
  89                 u8 *pos = dst + (GHASH_BLOCK_SIZE - dctx->bytes);
  90
  91                 dctx->bytes -= n;
  92                 srclen -= n;
  93
  94                 while (n--)
  95                         *pos++ ^= *src++;
  96
  97                 if (!dctx->bytes)
  98                         gf128mul_4k_lle((be128 *)dst, ctx->gf128);
  99         }
 100
 101         while (srclen >= GHASH_BLOCK_SIZE) {
 102                 crypto_xor(dst, src, GHASH_BLOCK_SIZE);
 103                 gf128mul_4k_lle((be128 *)dst, ctx->gf128);
 104                 src += GHASH_BLOCK_SIZE;
 105                 srclen -= GHASH_BLOCK_SIZE;
 106         }
 107
 108         if (srclen) {
 109                 dctx->bytes = GHASH_BLOCK_SIZE - srclen;
 110                 while (srclen--)
 111                         *dst++ ^= *src++;
 112         }
 113
 114         return 0;
 115 }
 116
 117 static void ghash_flush(struct ghash_ctx *ctx, struct ghash_desc_ctx *dctx)
 118 {
 119         u8 *dst = dctx->buffer;
 120
 121         if (dctx->bytes) {
 122                 u8 *tmp = dst + (GHASH_BLOCK_SIZE - dctx->bytes);
 123
 124                 while (dctx->bytes--)
 125                         *tmp++ ^= 0;
 126
 127                 gf128mul_4k_lle((be128 *)dst, ctx->gf128);
 128         }
 129
 130         dctx->bytes = 0;
 131 }
 132
 133 static int ghash_final(struct shash_desc *desc, u8 *dst)
 134 {
 135         struct ghash_desc_ctx *dctx = shash_desc_ctx(desc);
 136         struct ghash_ctx *ctx = crypto_shash_ctx(desc->tfm);
 137         u8 *buf = dctx->buffer;
 138
 139         ghash_flush(ctx, dctx);
 140         memcpy(dst, buf, GHASH_BLOCK_SIZE);
 141
 142         return 0;
 143 }
 144
 145 static void ghash_exit_tfm(struct crypto_tfm *tfm)
 146 {
 147         struct ghash_ctx *ctx = crypto_tfm_ctx(tfm);
 148         if (ctx->gf128)
 149                 gf128mul_free_4k(ctx->gf128);
 150 }
 151
 152 static struct shash_alg ghash_alg = {
 153         .digestsize     = GHASH_DIGEST_SIZE,
 154         .init           = ghash_init,
 155         .update         = ghash_update,
 156         .final          = ghash_final,
 157         .setkey         = ghash_setkey,
 158         .descsize       = sizeof(struct ghash_desc_ctx),
 159         .base           = {
 160                 .cra_name               = "ghash",
 161                 .cra_driver_name        = "ghash-generic",
 162                 .cra_priority           = 100,
 163                 .cra_blocksize          = GHASH_BLOCK_SIZE,
 164                 .cra_ctxsize            = sizeof(struct ghash_ctx),
 165                 .cra_module             = THIS_MODULE,
 166                 .cra_exit               = ghash_exit_tfm,
 167         },
 168 };
 169
 170 static int __init ghash_mod_init(void)
 171 {
 172         return crypto_register_shash(&ghash_alg);
 173 }
 174
 175 static void __exit ghash_mod_exit(void)
 176 {
 177         crypto_unregister_shash(&ghash_alg);
 178 }
 179
 180 subsys_initcall(ghash_mod_init);
 181 module_exit(ghash_mod_exit);
 182
 183 MODULE_LICENSE("GPL");
 184 MODULE_DESCRIPTION("GHASH hash function");
 185 MODULE_ALIAS_CRYPTO("ghash");
 186 MODULE_ALIAS_CRYPTO("ghash-generic");