xref: /kernel/linux/linux-5.10/crypto/ecdh.c (revision 8c2ecf20) 
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, &params) < 0 ||
43	    params.key_size > sizeof(ctx->private_key))
44		return -EINVAL;
45
46	ndigits = ecdh_supported_curve(params.curve_id);
47	if (!ndigits)
48		return -EINVAL;
49
50	ctx->curve_id = params.curve_id;
51	ctx->ndigits = ndigits;
52
53	if (!params.key || !params.key_size)
54		return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
55				       ctx->private_key);
56
57	memcpy(ctx->private_key, params.key, params.key_size);
58
59	if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
60			     ctx->private_key, params.key_size) < 0) {
61		memzero_explicit(ctx->private_key, params.key_size);
62		return -EINVAL;
63	}
64	return 0;
65}
66
67static int ecdh_compute_value(struct kpp_request *req)
68{
69	struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
70	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
71	u64 *public_key;
72	u64 *shared_secret = NULL;
73	void *buf;
74	size_t copied, nbytes, public_key_sz;
75	int ret = -ENOMEM;
76
77	nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
78	/* Public part is a point thus it has both coordinates */
79	public_key_sz = 2 * nbytes;
80
81	public_key = kmalloc(public_key_sz, GFP_KERNEL);
82	if (!public_key)
83		return -ENOMEM;
84
85	if (req->src) {
86		shared_secret = kmalloc(nbytes, GFP_KERNEL);
87		if (!shared_secret)
88			goto free_pubkey;
89
90		/* from here on it's invalid parameters */
91		ret = -EINVAL;
92
93		/* must have exactly two points to be on the curve */
94		if (public_key_sz != req->src_len)
95			goto free_all;
96
97		copied = sg_copy_to_buffer(req->src,
98					   sg_nents_for_len(req->src,
99							    public_key_sz),
100					   public_key, public_key_sz);
101		if (copied != public_key_sz)
102			goto free_all;
103
104		ret = crypto_ecdh_shared_secret(ctx->curve_id, ctx->ndigits,
105						ctx->private_key, public_key,
106						shared_secret);
107
108		buf = shared_secret;
109	} else {
110		ret = ecc_make_pub_key(ctx->curve_id, ctx->ndigits,
111				       ctx->private_key, public_key);
112		buf = public_key;
113		nbytes = public_key_sz;
114	}
115
116	if (ret < 0)
117		goto free_all;
118
119	/* might want less than we've got */
120	nbytes = min_t(size_t, nbytes, req->dst_len);
121	copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst,
122								nbytes),
123				     buf, nbytes);
124	if (copied != nbytes)
125		ret = -EINVAL;
126
127	/* fall through */
128free_all:
129	kfree_sensitive(shared_secret);
130free_pubkey:
131	kfree(public_key);
132	return ret;
133}
134
135static unsigned int ecdh_max_size(struct crypto_kpp *tfm)
136{
137	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
138
139	/* Public key is made of two coordinates, add one to the left shift */
140	return ctx->ndigits << (ECC_DIGITS_TO_BYTES_SHIFT + 1);
141}
142
143static struct kpp_alg ecdh = {
144	.set_secret = ecdh_set_secret,
145	.generate_public_key = ecdh_compute_value,
146	.compute_shared_secret = ecdh_compute_value,
147	.max_size = ecdh_max_size,
148	.base = {
149		.cra_name = "ecdh",
150		.cra_driver_name = "ecdh-generic",
151		.cra_priority = 100,
152		.cra_module = THIS_MODULE,
153		.cra_ctxsize = sizeof(struct ecdh_ctx),
154	},
155};
156
157static int ecdh_init(void)
158{
159	return crypto_register_kpp(&ecdh);
160}
161
162static void ecdh_exit(void)
163{
164	crypto_unregister_kpp(&ecdh);
165}
166
167subsys_initcall(ecdh_init);
168module_exit(ecdh_exit);
169MODULE_ALIAS_CRYPTO("ecdh");
170MODULE_LICENSE("GPL");
171MODULE_DESCRIPTION("ECDH generic algorithm");
172