xref: /linux/crypto/dh.c (revision 507e190946297c34a27d9366b0661d5e506fdd03)
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 
18 struct dh_ctx {
19 	MPI p;
20 	MPI g;
21 	MPI xa;
22 };
23 
24 static 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 
32 static 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  */
45 static 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 
51 static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm)
52 {
53 	return kpp_tfm_ctx(tfm);
54 }
55 
56 static int dh_check_params_length(unsigned int p_len)
57 {
58 	return (p_len < 1536) ? -EINVAL : 0;
59 }
60 
61 static 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 
82 static 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, &params) < 0)
92 		return -EINVAL;
93 
94 	if (dh_set_params(ctx, &params) < 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 
106 static 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;
142 err_free_base:
143 	if (req->src)
144 		mpi_free(base);
145 err_free_val:
146 	mpi_free(val);
147 	return ret;
148 }
149 
150 static 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 
157 static 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 
164 static 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 
179 static int dh_init(void)
180 {
181 	return crypto_register_kpp(&dh);
182 }
183 
184 static void dh_exit(void)
185 {
186 	crypto_unregister_kpp(&dh);
187 }
188 
189 module_init(dh_init);
190 module_exit(dh_exit);
191 MODULE_ALIAS_CRYPTO("dh");
192 MODULE_LICENSE("GPL");
193 MODULE_DESCRIPTION("DH generic algorithm");
194