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1// SPDX-License-Identifier: GPL-2.0-or-later
2/* ECDH key-agreement protocol
3 *
4 * Copyright (c) 2016, Intel Corporation
5 * Authors: Salvator 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/ecdh.h>
12#include <linux/scatterlist.h>
13#include "ecc.h"
14
15struct ecdh_ctx {
16 unsigned int curve_id;
17 unsigned int ndigits;
18 u64 private_key[ECC_MAX_DIGITS];
19};
20
21static inline struct ecdh_ctx *ecdh_get_ctx(struct crypto_kpp *tfm)
22{
23 return kpp_tfm_ctx(tfm);
24}
25
26static unsigned int ecdh_supported_curve(unsigned int curve_id)
27{
28 switch (curve_id) {
29 case ECC_CURVE_NIST_P192: return ECC_CURVE_NIST_P192_DIGITS;
30 case ECC_CURVE_NIST_P256: return ECC_CURVE_NIST_P256_DIGITS;
31 default: return 0;
32 }
33}
34
35static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
36 unsigned int len)
37{
38 struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
39 struct ecdh params;
40 unsigned int ndigits;
41
42 if (crypto_ecdh_decode_key(buf, len, ¶ms) < 0)
43 return -EINVAL;
44
45 ndigits = ecdh_supported_curve(params.curve_id);
46 if (!ndigits)
47 return -EINVAL;
48
49 ctx->curve_id = params.curve_id;
50 ctx->ndigits = ndigits;
51
52 if (!params.key || !params.key_size)
53 return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
54 ctx->private_key);
55
56 if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
57 (const u64 *)params.key, params.key_size) < 0)
58 return -EINVAL;
59
60 memcpy(ctx->private_key, params.key, params.key_size);
61
62 return 0;
63}
64
65static int ecdh_compute_value(struct kpp_request *req)
66{
67 struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
68 struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
69 u64 *public_key;
70 u64 *shared_secret = NULL;
71 void *buf;
72 size_t copied, nbytes, public_key_sz;
73 int ret = -ENOMEM;
74
75 nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
76 /* Public part is a point thus it has both coordinates */
77 public_key_sz = 2 * nbytes;
78
79 public_key = kmalloc(public_key_sz, GFP_KERNEL);
80 if (!public_key)
81 return -ENOMEM;
82
83 if (req->src) {
84 shared_secret = kmalloc(nbytes, GFP_KERNEL);
85 if (!shared_secret)
86 goto free_pubkey;
87
88 /* from here on it's invalid parameters */
89 ret = -EINVAL;
90
91 /* must have exactly two points to be on the curve */
92 if (public_key_sz != req->src_len)
93 goto free_all;
94
95 copied = sg_copy_to_buffer(req->src,
96 sg_nents_for_len(req->src,
97 public_key_sz),
98 public_key, public_key_sz);
99 if (copied != public_key_sz)
100 goto free_all;
101
102 ret = crypto_ecdh_shared_secret(ctx->curve_id, ctx->ndigits,
103 ctx->private_key, public_key,
104 shared_secret);
105
106 buf = shared_secret;
107 } else {
108 ret = ecc_make_pub_key(ctx->curve_id, ctx->ndigits,
109 ctx->private_key, public_key);
110 buf = public_key;
111 nbytes = public_key_sz;
112 }
113
114 if (ret < 0)
115 goto free_all;
116
117 /* might want less than we've got */
118 nbytes = min_t(size_t, nbytes, req->dst_len);
119 copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst,
120 nbytes),
121 buf, nbytes);
122 if (copied != nbytes)
123 ret = -EINVAL;
124
125 /* fall through */
126free_all:
127 kzfree(shared_secret);
128free_pubkey:
129 kfree(public_key);
130 return ret;
131}
132
133static unsigned int ecdh_max_size(struct crypto_kpp *tfm)
134{
135 struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
136
137 /* Public key is made of two coordinates, add one to the left shift */
138 return ctx->ndigits << (ECC_DIGITS_TO_BYTES_SHIFT + 1);
139}
140
141static struct kpp_alg ecdh = {
142 .set_secret = ecdh_set_secret,
143 .generate_public_key = ecdh_compute_value,
144 .compute_shared_secret = ecdh_compute_value,
145 .max_size = ecdh_max_size,
146 .base = {
147 .cra_name = "ecdh",
148 .cra_driver_name = "ecdh-generic",
149 .cra_priority = 100,
150 .cra_module = THIS_MODULE,
151 .cra_ctxsize = sizeof(struct ecdh_ctx),
152 },
153};
154
155static int ecdh_init(void)
156{
157 return crypto_register_kpp(&ecdh);
158}
159
160static void ecdh_exit(void)
161{
162 crypto_unregister_kpp(&ecdh);
163}
164
165subsys_initcall(ecdh_init);
166module_exit(ecdh_exit);
167MODULE_ALIAS_CRYPTO("ecdh");
168MODULE_LICENSE("GPL");
169MODULE_DESCRIPTION("ECDH generic algorithm");