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1/* Diffie-Hellman Key Agreement Method [RFC2631]
2 *
3 * Copyright (c) 2016, Intel Corporation
4 * Authors: Salvatore Benedetto <salvatore.benedetto@intel.com>
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License
8 * as published by the Free Software Foundation; either version
9 * 2 of the License, or (at your option) any later version.
10 */
11
12#include <linux/module.h>
13#include <crypto/internal/kpp.h>
14#include <crypto/kpp.h>
15#include <crypto/dh.h>
16#include <linux/mpi.h>
17
18struct dh_ctx {
19 MPI p;
20 MPI g;
21 MPI xa;
22};
23
24static inline void dh_clear_params(struct dh_ctx *ctx)
25{
26 mpi_free(ctx->p);
27 mpi_free(ctx->g);
28 ctx->p = NULL;
29 ctx->g = NULL;
30}
31
32static void dh_free_ctx(struct dh_ctx *ctx)
33{
34 dh_clear_params(ctx);
35 mpi_free(ctx->xa);
36 ctx->xa = NULL;
37}
38
39/*
40 * If base is g we compute the public key
41 * ya = g^xa mod p; [RFC2631 sec 2.1.1]
42 * else if base if the counterpart public key we compute the shared secret
43 * ZZ = yb^xa mod p; [RFC2631 sec 2.1.1]
44 */
45static int _compute_val(const struct dh_ctx *ctx, MPI base, MPI val)
46{
47 /* val = base^xa mod p */
48 return mpi_powm(val, base, ctx->xa, ctx->p);
49}
50
51static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm)
52{
53 return kpp_tfm_ctx(tfm);
54}
55
56static int dh_check_params_length(unsigned int p_len)
57{
58 return (p_len < 1536) ? -EINVAL : 0;
59}
60
61static int dh_set_params(struct dh_ctx *ctx, struct dh *params)
62{
63 if (unlikely(!params->p || !params->g))
64 return -EINVAL;
65
66 if (dh_check_params_length(params->p_size << 3))
67 return -EINVAL;
68
69 ctx->p = mpi_read_raw_data(params->p, params->p_size);
70 if (!ctx->p)
71 return -EINVAL;
72
73 ctx->g = mpi_read_raw_data(params->g, params->g_size);
74 if (!ctx->g) {
75 mpi_free(ctx->p);
76 return -EINVAL;
77 }
78
79 return 0;
80}
81
82static int dh_set_secret(struct crypto_kpp *tfm, const void *buf,
83 unsigned int len)
84{
85 struct dh_ctx *ctx = dh_get_ctx(tfm);
86 struct dh params;
87
88 /* Free the old MPI key if any */
89 dh_free_ctx(ctx);
90
91 if (crypto_dh_decode_key(buf, len, ¶ms) < 0)
92 return -EINVAL;
93
94 if (dh_set_params(ctx, ¶ms) < 0)
95 return -EINVAL;
96
97 ctx->xa = mpi_read_raw_data(params.key, params.key_size);
98 if (!ctx->xa) {
99 dh_clear_params(ctx);
100 return -EINVAL;
101 }
102
103 return 0;
104}
105
106static int dh_compute_value(struct kpp_request *req)
107{
108 struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
109 struct dh_ctx *ctx = dh_get_ctx(tfm);
110 MPI base, val = mpi_alloc(0);
111 int ret = 0;
112 int sign;
113
114 if (!val)
115 return -ENOMEM;
116
117 if (unlikely(!ctx->xa)) {
118 ret = -EINVAL;
119 goto err_free_val;
120 }
121
122 if (req->src) {
123 base = mpi_read_raw_from_sgl(req->src, req->src_len);
124 if (!base) {
125 ret = -EINVAL;
126 goto err_free_val;
127 }
128 } else {
129 base = ctx->g;
130 }
131
132 ret = _compute_val(ctx, base, val);
133 if (ret)
134 goto err_free_base;
135
136 ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign);
137 if (ret)
138 goto err_free_base;
139
140 if (sign < 0)
141 ret = -EBADMSG;
142err_free_base:
143 if (req->src)
144 mpi_free(base);
145err_free_val:
146 mpi_free(val);
147 return ret;
148}
149
150static unsigned int dh_max_size(struct crypto_kpp *tfm)
151{
152 struct dh_ctx *ctx = dh_get_ctx(tfm);
153
154 return mpi_get_size(ctx->p);
155}
156
157static void dh_exit_tfm(struct crypto_kpp *tfm)
158{
159 struct dh_ctx *ctx = dh_get_ctx(tfm);
160
161 dh_free_ctx(ctx);
162}
163
164static struct kpp_alg dh = {
165 .set_secret = dh_set_secret,
166 .generate_public_key = dh_compute_value,
167 .compute_shared_secret = dh_compute_value,
168 .max_size = dh_max_size,
169 .exit = dh_exit_tfm,
170 .base = {
171 .cra_name = "dh",
172 .cra_driver_name = "dh-generic",
173 .cra_priority = 100,
174 .cra_module = THIS_MODULE,
175 .cra_ctxsize = sizeof(struct dh_ctx),
176 },
177};
178
179static int dh_init(void)
180{
181 return crypto_register_kpp(&dh);
182}
183
184static void dh_exit(void)
185{
186 crypto_unregister_kpp(&dh);
187}
188
189module_init(dh_init);
190module_exit(dh_exit);
191MODULE_ALIAS_CRYPTO("dh");
192MODULE_LICENSE("GPL");
193MODULE_DESCRIPTION("DH generic algorithm");