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"); 185