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 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/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	u64 public_key[2 * ECC_MAX_DIGITS];
 24	u64 shared_secret[ECC_MAX_DIGITS];
 25};
 26
 27static inline struct ecdh_ctx *ecdh_get_ctx(struct crypto_kpp *tfm)
 28{
 29	return kpp_tfm_ctx(tfm);
 30}
 31
 32static unsigned int ecdh_supported_curve(unsigned int curve_id)
 33{
 34	switch (curve_id) {
 35	case ECC_CURVE_NIST_P192: return 3;
 36	case ECC_CURVE_NIST_P256: return 4;
 37	default: return 0;
 38	}
 39}
 40
 41static int ecdh_set_secret(struct crypto_kpp *tfm, void *buf, unsigned int len)
 42{
 43	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
 44	struct ecdh params;
 45	unsigned int ndigits;
 46
 47	if (crypto_ecdh_decode_key(buf, len, &params) < 0)
 48		return -EINVAL;
 49
 50	ndigits = ecdh_supported_curve(params.curve_id);
 51	if (!ndigits)
 52		return -EINVAL;
 53
 54	ctx->curve_id = params.curve_id;
 55	ctx->ndigits = ndigits;
 56
 57	if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
 58			     (const u8 *)params.key, params.key_size) < 0)
 59		return -EINVAL;
 60
 61	memcpy(ctx->private_key, params.key, params.key_size);
 62
 63	return 0;
 64}
 65
 66static int ecdh_compute_value(struct kpp_request *req)
 67{
 68	int ret = 0;
 69	struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
 70	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
 71	size_t copied, nbytes;
 72	void *buf;
 73
 74	nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
 75
 76	if (req->src) {
 77		copied = sg_copy_to_buffer(req->src, 1, ctx->public_key,
 78					   2 * nbytes);
 79		if (copied != 2 * nbytes)
 80			return -EINVAL;
 81
 82		ret = crypto_ecdh_shared_secret(ctx->curve_id, ctx->ndigits,
 83					 (const u8 *)ctx->private_key, nbytes,
 84					 (const u8 *)ctx->public_key, 2 * nbytes,
 85					 (u8 *)ctx->shared_secret, nbytes);
 86
 87		buf = ctx->shared_secret;
 88	} else {
 89		ret = ecdh_make_pub_key(ctx->curve_id, ctx->ndigits,
 90					(const u8 *)ctx->private_key, nbytes,
 91					(u8 *)ctx->public_key,
 92					sizeof(ctx->public_key));
 93		buf = ctx->public_key;
 94		/* Public part is a point thus it has both coordinates */
 95		nbytes *= 2;
 96	}
 97
 98	if (ret < 0)
 99		return ret;
100
101	copied = sg_copy_from_buffer(req->dst, 1, buf, nbytes);
102	if (copied != nbytes)
103		return -EINVAL;
104
105	return ret;
106}
107
108static int ecdh_max_size(struct crypto_kpp *tfm)
109{
110	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
111	int nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
112
113	/* Public key is made of two coordinates */
114	return 2 * nbytes;
115}
116
117static void no_exit_tfm(struct crypto_kpp *tfm)
118{
119	return;
120}
121
122static struct kpp_alg ecdh = {
123	.set_secret = ecdh_set_secret,
124	.generate_public_key = ecdh_compute_value,
125	.compute_shared_secret = ecdh_compute_value,
126	.max_size = ecdh_max_size,
127	.exit = no_exit_tfm,
128	.base = {
129		.cra_name = "ecdh",
130		.cra_driver_name = "ecdh-generic",
131		.cra_priority = 100,
132		.cra_module = THIS_MODULE,
133		.cra_ctxsize = sizeof(struct ecdh_ctx),
134	},
135};
136
137static int ecdh_init(void)
138{
139	return crypto_register_kpp(&ecdh);
140}
141
142static void ecdh_exit(void)
143{
144	crypto_unregister_kpp(&ecdh);
145}
146
147module_init(ecdh_init);
148module_exit(ecdh_exit);
149MODULE_ALIAS_CRYPTO("ecdh");
150MODULE_LICENSE("GPL");
151MODULE_DESCRIPTION("ECDH generic algorithm");