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 Licence
8 * as published by the Free Software Foundation; either version
9 * 2 of the Licence, 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
dh_clear_ctx(struct dh_ctx * ctx)24 static void dh_clear_ctx(struct dh_ctx *ctx)
25 {
26 mpi_free(ctx->p);
27 mpi_free(ctx->g);
28 mpi_free(ctx->xa);
29 memset(ctx, 0, sizeof(*ctx));
30 }
31
32 /*
33 * If base is g we compute the public key
34 * ya = g^xa mod p; [RFC2631 sec 2.1.1]
35 * else if base if the counterpart public key we compute the shared secret
36 * ZZ = yb^xa mod p; [RFC2631 sec 2.1.1]
37 */
_compute_val(const struct dh_ctx * ctx,MPI base,MPI val)38 static int _compute_val(const struct dh_ctx *ctx, MPI base, MPI val)
39 {
40 /* val = base^xa mod p */
41 return mpi_powm(val, base, ctx->xa, ctx->p);
42 }
43
dh_get_ctx(struct crypto_kpp * tfm)44 static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm)
45 {
46 return kpp_tfm_ctx(tfm);
47 }
48
dh_check_params_length(unsigned int p_len)49 static int dh_check_params_length(unsigned int p_len)
50 {
51 return (p_len < 1536) ? -EINVAL : 0;
52 }
53
dh_set_params(struct dh_ctx * ctx,struct dh * params)54 static int dh_set_params(struct dh_ctx *ctx, struct dh *params)
55 {
56 if (unlikely(!params->p || !params->g))
57 return -EINVAL;
58
59 if (dh_check_params_length(params->p_size << 3))
60 return -EINVAL;
61
62 ctx->p = mpi_read_raw_data(params->p, params->p_size);
63 if (!ctx->p)
64 return -EINVAL;
65
66 ctx->g = mpi_read_raw_data(params->g, params->g_size);
67 if (!ctx->g)
68 return -EINVAL;
69
70 return 0;
71 }
72
dh_set_secret(struct crypto_kpp * tfm,void * buf,unsigned int len)73 static int dh_set_secret(struct crypto_kpp *tfm, void *buf, unsigned int len)
74 {
75 struct dh_ctx *ctx = dh_get_ctx(tfm);
76 struct dh params;
77
78 /* Free the old MPI key if any */
79 dh_clear_ctx(ctx);
80
81 if (crypto_dh_decode_key(buf, len, ¶ms) < 0)
82 goto err_clear_ctx;
83
84 if (dh_set_params(ctx, ¶ms) < 0)
85 goto err_clear_ctx;
86
87 ctx->xa = mpi_read_raw_data(params.key, params.key_size);
88 if (!ctx->xa)
89 goto err_clear_ctx;
90
91 return 0;
92
93 err_clear_ctx:
94 dh_clear_ctx(ctx);
95 return -EINVAL;
96 }
97
dh_compute_value(struct kpp_request * req)98 static int dh_compute_value(struct kpp_request *req)
99 {
100 struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
101 struct dh_ctx *ctx = dh_get_ctx(tfm);
102 MPI base, val = mpi_alloc(0);
103 int ret = 0;
104 int sign;
105
106 if (!val)
107 return -ENOMEM;
108
109 if (unlikely(!ctx->xa)) {
110 ret = -EINVAL;
111 goto err_free_val;
112 }
113
114 if (req->src) {
115 base = mpi_read_raw_from_sgl(req->src, req->src_len);
116 if (!base) {
117 ret = EINVAL;
118 goto err_free_val;
119 }
120 } else {
121 base = ctx->g;
122 }
123
124 ret = _compute_val(ctx, base, val);
125 if (ret)
126 goto err_free_base;
127
128 ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign);
129 if (ret)
130 goto err_free_base;
131
132 if (sign < 0)
133 ret = -EBADMSG;
134 err_free_base:
135 if (req->src)
136 mpi_free(base);
137 err_free_val:
138 mpi_free(val);
139 return ret;
140 }
141
dh_max_size(struct crypto_kpp * tfm)142 static int dh_max_size(struct crypto_kpp *tfm)
143 {
144 struct dh_ctx *ctx = dh_get_ctx(tfm);
145
146 return mpi_get_size(ctx->p);
147 }
148
dh_exit_tfm(struct crypto_kpp * tfm)149 static void dh_exit_tfm(struct crypto_kpp *tfm)
150 {
151 struct dh_ctx *ctx = dh_get_ctx(tfm);
152
153 dh_clear_ctx(ctx);
154 }
155
156 static struct kpp_alg dh = {
157 .set_secret = dh_set_secret,
158 .generate_public_key = dh_compute_value,
159 .compute_shared_secret = dh_compute_value,
160 .max_size = dh_max_size,
161 .exit = dh_exit_tfm,
162 .base = {
163 .cra_name = "dh",
164 .cra_driver_name = "dh-generic",
165 .cra_priority = 100,
166 .cra_module = THIS_MODULE,
167 .cra_ctxsize = sizeof(struct dh_ctx),
168 },
169 };
170
dh_init(void)171 static int dh_init(void)
172 {
173 return crypto_register_kpp(&dh);
174 }
175
dh_exit(void)176 static void dh_exit(void)
177 {
178 crypto_unregister_kpp(&dh);
179 }
180
181 module_init(dh_init);
182 module_exit(dh_exit);
183 MODULE_ALIAS_CRYPTO("dh");
184 MODULE_LICENSE("GPL");
185 MODULE_DESCRIPTION("DH generic algorithm");
186