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1// SPDX-License-Identifier: GPL-2.0-or-later
2/* Diffie-Hellman Key Agreement Method [RFC2631]
3 *
4 * Copyright (c) 2016, Intel Corporation
5 * Authors: Salvatore Benedetto <salvatore.benedetto@intel.com>
6 */
7
8#include <linux/module.h>
9#include <crypto/internal/kpp.h>
10#include <crypto/kpp.h>
11#include <crypto/dh.h>
12#include <linux/fips.h>
13#include <linux/mpi.h>
14
15struct dh_ctx {
16 MPI p; /* Value is guaranteed to be set. */
17 MPI q; /* Value is optional. */
18 MPI g; /* Value is guaranteed to be set. */
19 MPI xa; /* Value is guaranteed to be set. */
20};
21
22static void dh_clear_ctx(struct dh_ctx *ctx)
23{
24 mpi_free(ctx->p);
25 mpi_free(ctx->q);
26 mpi_free(ctx->g);
27 mpi_free(ctx->xa);
28 memset(ctx, 0, sizeof(*ctx));
29}
30
31/*
32 * If base is g we compute the public key
33 * ya = g^xa mod p; [RFC2631 sec 2.1.1]
34 * else if base if the counterpart public key we compute the shared secret
35 * ZZ = yb^xa mod p; [RFC2631 sec 2.1.1]
36 */
37static int _compute_val(const struct dh_ctx *ctx, MPI base, MPI val)
38{
39 /* val = base^xa mod p */
40 return mpi_powm(val, base, ctx->xa, ctx->p);
41}
42
43static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm)
44{
45 return kpp_tfm_ctx(tfm);
46}
47
48static int dh_check_params_length(unsigned int p_len)
49{
50 return (p_len < 1536) ? -EINVAL : 0;
51}
52
53static int dh_set_params(struct dh_ctx *ctx, struct dh *params)
54{
55 if (dh_check_params_length(params->p_size << 3))
56 return -EINVAL;
57
58 ctx->p = mpi_read_raw_data(params->p, params->p_size);
59 if (!ctx->p)
60 return -EINVAL;
61
62 if (params->q && params->q_size) {
63 ctx->q = mpi_read_raw_data(params->q, params->q_size);
64 if (!ctx->q)
65 return -EINVAL;
66 }
67
68 ctx->g = mpi_read_raw_data(params->g, params->g_size);
69 if (!ctx->g)
70 return -EINVAL;
71
72 return 0;
73}
74
75static int dh_set_secret(struct crypto_kpp *tfm, const void *buf,
76 unsigned int len)
77{
78 struct dh_ctx *ctx = dh_get_ctx(tfm);
79 struct dh params;
80
81 /* Free the old MPI key if any */
82 dh_clear_ctx(ctx);
83
84 if (crypto_dh_decode_key(buf, len, ¶ms) < 0)
85 goto err_clear_ctx;
86
87 if (dh_set_params(ctx, ¶ms) < 0)
88 goto err_clear_ctx;
89
90 ctx->xa = mpi_read_raw_data(params.key, params.key_size);
91 if (!ctx->xa)
92 goto err_clear_ctx;
93
94 return 0;
95
96err_clear_ctx:
97 dh_clear_ctx(ctx);
98 return -EINVAL;
99}
100
101/*
102 * SP800-56A public key verification:
103 *
104 * * If Q is provided as part of the domain paramenters, a full validation
105 * according to SP800-56A section 5.6.2.3.1 is performed.
106 *
107 * * If Q is not provided, a partial validation according to SP800-56A section
108 * 5.6.2.3.2 is performed.
109 */
110static int dh_is_pubkey_valid(struct dh_ctx *ctx, MPI y)
111{
112 if (unlikely(!ctx->p))
113 return -EINVAL;
114
115 /*
116 * Step 1: Verify that 2 <= y <= p - 2.
117 *
118 * The upper limit check is actually y < p instead of y < p - 1
119 * as the mpi_sub_ui function is yet missing.
120 */
121 if (mpi_cmp_ui(y, 1) < 1 || mpi_cmp(y, ctx->p) >= 0)
122 return -EINVAL;
123
124 /* Step 2: Verify that 1 = y^q mod p */
125 if (ctx->q) {
126 MPI val = mpi_alloc(0);
127 int ret;
128
129 if (!val)
130 return -ENOMEM;
131
132 ret = mpi_powm(val, y, ctx->q, ctx->p);
133
134 if (ret) {
135 mpi_free(val);
136 return ret;
137 }
138
139 ret = mpi_cmp_ui(val, 1);
140
141 mpi_free(val);
142
143 if (ret != 0)
144 return -EINVAL;
145 }
146
147 return 0;
148}
149
150static int dh_compute_value(struct kpp_request *req)
151{
152 struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
153 struct dh_ctx *ctx = dh_get_ctx(tfm);
154 MPI base, val = mpi_alloc(0);
155 int ret = 0;
156 int sign;
157
158 if (!val)
159 return -ENOMEM;
160
161 if (unlikely(!ctx->xa)) {
162 ret = -EINVAL;
163 goto err_free_val;
164 }
165
166 if (req->src) {
167 base = mpi_read_raw_from_sgl(req->src, req->src_len);
168 if (!base) {
169 ret = -EINVAL;
170 goto err_free_val;
171 }
172 ret = dh_is_pubkey_valid(ctx, base);
173 if (ret)
174 goto err_free_base;
175 } else {
176 base = ctx->g;
177 }
178
179 ret = _compute_val(ctx, base, val);
180 if (ret)
181 goto err_free_base;
182
183 if (fips_enabled) {
184 /* SP800-56A rev3 5.7.1.1 check: Validation of shared secret */
185 if (req->src) {
186 MPI pone;
187
188 /* z <= 1 */
189 if (mpi_cmp_ui(val, 1) < 1) {
190 ret = -EBADMSG;
191 goto err_free_base;
192 }
193
194 /* z == p - 1 */
195 pone = mpi_alloc(0);
196
197 if (!pone) {
198 ret = -ENOMEM;
199 goto err_free_base;
200 }
201
202 ret = mpi_sub_ui(pone, ctx->p, 1);
203 if (!ret && !mpi_cmp(pone, val))
204 ret = -EBADMSG;
205
206 mpi_free(pone);
207
208 if (ret)
209 goto err_free_base;
210
211 /* SP800-56A rev 3 5.6.2.1.3 key check */
212 } else {
213 if (dh_is_pubkey_valid(ctx, val)) {
214 ret = -EAGAIN;
215 goto err_free_val;
216 }
217 }
218 }
219
220 ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign);
221 if (ret)
222 goto err_free_base;
223
224 if (sign < 0)
225 ret = -EBADMSG;
226err_free_base:
227 if (req->src)
228 mpi_free(base);
229err_free_val:
230 mpi_free(val);
231 return ret;
232}
233
234static unsigned int dh_max_size(struct crypto_kpp *tfm)
235{
236 struct dh_ctx *ctx = dh_get_ctx(tfm);
237
238 return mpi_get_size(ctx->p);
239}
240
241static void dh_exit_tfm(struct crypto_kpp *tfm)
242{
243 struct dh_ctx *ctx = dh_get_ctx(tfm);
244
245 dh_clear_ctx(ctx);
246}
247
248static struct kpp_alg dh = {
249 .set_secret = dh_set_secret,
250 .generate_public_key = dh_compute_value,
251 .compute_shared_secret = dh_compute_value,
252 .max_size = dh_max_size,
253 .exit = dh_exit_tfm,
254 .base = {
255 .cra_name = "dh",
256 .cra_driver_name = "dh-generic",
257 .cra_priority = 100,
258 .cra_module = THIS_MODULE,
259 .cra_ctxsize = sizeof(struct dh_ctx),
260 },
261};
262
263static int dh_init(void)
264{
265 return crypto_register_kpp(&dh);
266}
267
268static void dh_exit(void)
269{
270 crypto_unregister_kpp(&dh);
271}
272
273subsys_initcall(dh_init);
274module_exit(dh_exit);
275MODULE_ALIAS_CRYPTO("dh");
276MODULE_LICENSE("GPL");
277MODULE_DESCRIPTION("DH generic algorithm");