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		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");