aboutsummaryrefslogtreecommitdiff
path: root/crypto/dh.c
blob: 5659fe7f446d930973059422b1177d79f29b8451 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
/*  Diffie-Hellman Key Agreement Method [RFC2631]
 *
 * Copyright (c) 2016, Intel Corporation
 * Authors: Salvatore Benedetto <salvatore.benedetto@intel.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/module.h>
#include <crypto/internal/kpp.h>
#include <crypto/kpp.h>
#include <crypto/dh.h>
#include <linux/mpi.h>

struct dh_ctx {
	MPI p;
	MPI g;
	MPI xa;
};

static void dh_clear_ctx(struct dh_ctx *ctx)
{
	mpi_free(ctx->p);
	mpi_free(ctx->g);
	mpi_free(ctx->xa);
	memset(ctx, 0, sizeof(*ctx));
}

/*
 * If base is g we compute the public key
 *	ya = g^xa mod p; [RFC2631 sec 2.1.1]
 * else if base if the counterpart public key we compute the shared secret
 *	ZZ = yb^xa mod p; [RFC2631 sec 2.1.1]
 */
static int _compute_val(const struct dh_ctx *ctx, MPI base, MPI val)
{
	/* val = base^xa mod p */
	return mpi_powm(val, base, ctx->xa, ctx->p);
}

static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm)
{
	return kpp_tfm_ctx(tfm);
}

static int dh_check_params_length(unsigned int p_len)
{
	return (p_len < 1536) ? -EINVAL : 0;
}

static int dh_set_params(struct dh_ctx *ctx, struct dh *params)
{
	if (dh_check_params_length(params->p_size << 3))
		return -EINVAL;

	ctx->p = mpi_read_raw_data(params->p, params->p_size);
	if (!ctx->p)
		return -EINVAL;

	ctx->g = mpi_read_raw_data(params->g, params->g_size);
	if (!ctx->g)
		return -EINVAL;

	return 0;
}

static int dh_set_secret(struct crypto_kpp *tfm, const void *buf,
			 unsigned int len)
{
	struct dh_ctx *ctx = dh_get_ctx(tfm);
	struct dh params;

	/* Free the old MPI key if any */
	dh_clear_ctx(ctx);

	if (crypto_dh_decode_key(buf, len, &params) < 0)
		goto err_clear_ctx;

	if (dh_set_params(ctx, &params) < 0)
		goto err_clear_ctx;

	ctx->xa = mpi_read_raw_data(params.key, params.key_size);
	if (!ctx->xa)
		goto err_clear_ctx;

	return 0;

err_clear_ctx:
	dh_clear_ctx(ctx);
	return -EINVAL;
}

static int dh_compute_value(struct kpp_request *req)
{
	struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
	struct dh_ctx *ctx = dh_get_ctx(tfm);
	MPI base, val = mpi_alloc(0);
	int ret = 0;
	int sign;

	if (!val)
		return -ENOMEM;

	if (unlikely(!ctx->xa)) {
		ret = -EINVAL;
		goto err_free_val;
	}

	if (req->src) {
		base = mpi_read_raw_from_sgl(req->src, req->src_len);
		if (!base) {
			ret = -EINVAL;
			goto err_free_val;
		}
	} else {
		base = ctx->g;
	}

	ret = _compute_val(ctx, base, val);
	if (ret)
		goto err_free_base;

	ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign);
	if (ret)
		goto err_free_base;

	if (sign < 0)
		ret = -EBADMSG;
err_free_base:
	if (req->src)
		mpi_free(base);
err_free_val:
	mpi_free(val);
	return ret;
}

static unsigned int dh_max_size(struct crypto_kpp *tfm)
{
	struct dh_ctx *ctx = dh_get_ctx(tfm);

	return mpi_get_size(ctx->p);
}

static void dh_exit_tfm(struct crypto_kpp *tfm)
{
	struct dh_ctx *ctx = dh_get_ctx(tfm);

	dh_clear_ctx(ctx);
}

static struct kpp_alg dh = {
	.set_secret = dh_set_secret,
	.generate_public_key = dh_compute_value,
	.compute_shared_secret = dh_compute_value,
	.max_size = dh_max_size,
	.exit = dh_exit_tfm,
	.base = {
		.cra_name = "dh",
		.cra_driver_name = "dh-generic",
		.cra_priority = 100,
		.cra_module = THIS_MODULE,
		.cra_ctxsize = sizeof(struct dh_ctx),
	},
};

static int dh_init(void)
{
	return crypto_register_kpp(&dh);
}

static void dh_exit(void)
{
	crypto_unregister_kpp(&dh);
}

module_init(dh_init);
module_exit(dh_exit);
MODULE_ALIAS_CRYPTO("dh");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("DH generic algorithm");