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/gf128mul.h> 38 #include <crypto/ghash.h> 39 #include <crypto/internal/hash.h> 40 #include <crypto/utils.h> 41 #include <linux/err.h> 42 #include <linux/kernel.h> 43 #include <linux/module.h> 44 #include <linux/string.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 do { 86 crypto_xor(dst, src, GHASH_BLOCK_SIZE); 87 gf128mul_4k_lle((be128 *)dst, ctx->gf128); 88 src += GHASH_BLOCK_SIZE; 89 srclen -= GHASH_BLOCK_SIZE; 90 } while (srclen >= GHASH_BLOCK_SIZE); 91 92 return srclen; 93 } 94 95 static void ghash_flush(struct shash_desc *desc, const u8 *src, 96 unsigned int len) 97 { 98 struct ghash_ctx *ctx = crypto_shash_ctx(desc->tfm); 99 struct ghash_desc_ctx *dctx = shash_desc_ctx(desc); 100 u8 *dst = dctx->buffer; 101 102 if (len) { 103 crypto_xor(dst, src, len); 104 gf128mul_4k_lle((be128 *)dst, ctx->gf128); 105 } 106 } 107 108 static int ghash_finup(struct shash_desc *desc, const u8 *src, 109 unsigned int len, u8 *dst) 110 { 111 struct ghash_desc_ctx *dctx = shash_desc_ctx(desc); 112 u8 *buf = dctx->buffer; 113 114 ghash_flush(desc, src, len); 115 memcpy(dst, buf, GHASH_BLOCK_SIZE); 116 117 return 0; 118 } 119 120 static void ghash_exit_tfm(struct crypto_tfm *tfm) 121 { 122 struct ghash_ctx *ctx = crypto_tfm_ctx(tfm); 123 if (ctx->gf128) 124 gf128mul_free_4k(ctx->gf128); 125 } 126 127 static struct shash_alg ghash_alg = { 128 .digestsize = GHASH_DIGEST_SIZE, 129 .init = ghash_init, 130 .update = ghash_update, 131 .finup = ghash_finup, 132 .setkey = ghash_setkey, 133 .descsize = sizeof(struct ghash_desc_ctx), 134 .base = { 135 .cra_name = "ghash", 136 .cra_driver_name = "ghash-generic", 137 .cra_priority = 100, 138 .cra_flags = CRYPTO_AHASH_ALG_BLOCK_ONLY, 139 .cra_blocksize = GHASH_BLOCK_SIZE, 140 .cra_ctxsize = sizeof(struct ghash_ctx), 141 .cra_module = THIS_MODULE, 142 .cra_exit = ghash_exit_tfm, 143 }, 144 }; 145 146 static int __init ghash_mod_init(void) 147 { 148 return crypto_register_shash(&ghash_alg); 149 } 150 151 static void __exit ghash_mod_exit(void) 152 { 153 crypto_unregister_shash(&ghash_alg); 154 } 155 156 module_init(ghash_mod_init); 157 module_exit(ghash_mod_exit); 158 159 MODULE_LICENSE("GPL"); 160 MODULE_DESCRIPTION("GHASH hash function"); 161 MODULE_ALIAS_CRYPTO("ghash"); 162 MODULE_ALIAS_CRYPTO("ghash-generic"); 163