1/* ECDH key-agreement protocol
  2 *
  3 * Copyright (c) 2016, Intel Corporation
  4 * Authors: Salvator 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/ecdh.h>
 16#include <linux/scatterlist.h>
 17#include "ecc.h"
 18
 19struct ecdh_ctx {
 20	unsigned int curve_id;
 21	unsigned int ndigits;
 22	u64 private_key[ECC_MAX_DIGITS];
 23};
 24
 25static inline struct ecdh_ctx *ecdh_get_ctx(struct crypto_kpp *tfm)
 26{
 27	return kpp_tfm_ctx(tfm);
 28}
 29
 30static unsigned int ecdh_supported_curve(unsigned int curve_id)
 31{
 32	switch (curve_id) {
 33	case ECC_CURVE_NIST_P192: return 3;
 34	case ECC_CURVE_NIST_P256: return 4;
 35	default: return 0;
 36	}
 37}
 38
 39static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
 40			   unsigned int len)
 41{
 42	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
 43	struct ecdh params;
 44	unsigned int ndigits;
 45
 46	if (crypto_ecdh_decode_key(buf, len, &params) < 0)
 47		return -EINVAL;
 48
 49	ndigits = ecdh_supported_curve(params.curve_id);
 50	if (!ndigits)
 51		return -EINVAL;
 52
 53	ctx->curve_id = params.curve_id;
 54	ctx->ndigits = ndigits;
 55
 56	if (!params.key || !params.key_size)
 57		return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
 58				       ctx->private_key);
 59
 60	if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
 61			     (const u64 *)params.key, params.key_size) < 0)
 62		return -EINVAL;
 63
 64	memcpy(ctx->private_key, params.key, params.key_size);
 65
 66	return 0;
 67}
 68
 69static int ecdh_compute_value(struct kpp_request *req)
 70{
 71	struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
 72	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
 73	u64 *public_key;
 74	u64 *shared_secret = NULL;
 75	void *buf;
 76	size_t copied, nbytes, public_key_sz;
 77	int ret = -ENOMEM;
 78
 79	nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
 80	/* Public part is a point thus it has both coordinates */
 81	public_key_sz = 2 * nbytes;
 82
 83	public_key = kmalloc(public_key_sz, GFP_KERNEL);
 84	if (!public_key)
 85		return -ENOMEM;
 86
 87	if (req->src) {
 88		shared_secret = kmalloc(nbytes, GFP_KERNEL);
 89		if (!shared_secret)
 90			goto free_pubkey;
 91
 92		/* from here on it's invalid parameters */
 93		ret = -EINVAL;
 94
 95		/* must have exactly two points to be on the curve */
 96		if (public_key_sz != req->src_len)
 97			goto free_all;
 98
 99		copied = sg_copy_to_buffer(req->src,
100					   sg_nents_for_len(req->src,
101							    public_key_sz),
102					   public_key, public_key_sz);
103		if (copied != public_key_sz)
104			goto free_all;
105
106		ret = crypto_ecdh_shared_secret(ctx->curve_id, ctx->ndigits,
107						ctx->private_key, public_key,
108						shared_secret);
109
110		buf = shared_secret;
111	} else {
112		ret = ecc_make_pub_key(ctx->curve_id, ctx->ndigits,
113				       ctx->private_key, public_key);
114		buf = public_key;
115		nbytes = public_key_sz;
116	}
117
118	if (ret < 0)
119		goto free_all;
120
121	/* might want less than we've got */
122	nbytes = min_t(size_t, nbytes, req->dst_len);
123	copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst,
124								nbytes),
125				     buf, nbytes);
126	if (copied != nbytes)
127		ret = -EINVAL;
128
129	/* fall through */
130free_all:
131	kzfree(shared_secret);
132free_pubkey:
133	kfree(public_key);
134	return ret;
135}
136
137static unsigned int ecdh_max_size(struct crypto_kpp *tfm)
138{
139	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
140
141	/* Public key is made of two coordinates, add one to the left shift */
142	return ctx->ndigits << (ECC_DIGITS_TO_BYTES_SHIFT + 1);
143}
144
145static struct kpp_alg ecdh = {
146	.set_secret = ecdh_set_secret,
147	.generate_public_key = ecdh_compute_value,
148	.compute_shared_secret = ecdh_compute_value,
149	.max_size = ecdh_max_size,
150	.base = {
151		.cra_name = "ecdh",
152		.cra_driver_name = "ecdh-generic",
153		.cra_priority = 100,
154		.cra_module = THIS_MODULE,
155		.cra_ctxsize = sizeof(struct ecdh_ctx),
156	},
157};
158
159static int ecdh_init(void)
160{
161	return crypto_register_kpp(&ecdh);
162}
163
164static void ecdh_exit(void)
165{
166	crypto_unregister_kpp(&ecdh);
167}
168
169module_init(ecdh_init);
170module_exit(ecdh_exit);
171MODULE_ALIAS_CRYPTO("ecdh");
172MODULE_LICENSE("GPL");
173MODULE_DESCRIPTION("ECDH generic algorithm");