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(t: 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(g: &k); |
70 | memzero_explicit(s: &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(tfm: 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(a: (be128 *)dst, t: ctx->gf128); |
97 | } |
98 | |
99 | while (srclen >= GHASH_BLOCK_SIZE) { |
100 | crypto_xor(dst, src, GHASH_BLOCK_SIZE); |
101 | gf128mul_4k_lle(a: (be128 *)dst, t: 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(a: (be128 *)dst, t: 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(tfm: 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(t: 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(alg: &ghash_alg); |
171 | } |
172 | |
173 | static void __exit ghash_mod_exit(void) |
174 | { |
175 | crypto_unregister_shash(alg: &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 | |