tls13_key_share.c

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Author : jsing
Date : 2020-04-18 14:07:56
Hash : 501dd9a5
Message : Expose the peer ephemeral public key used for TLSv1.3 key exchange. SSL_get_server_tmp_key() provides the peer ephemeral public key used for key exchange. In the case of TLSv1.3 this is essentially the peer public key from the key share used for TLSv1.3 key exchange, hence make it availaable via SSL_get_server_tmp_key(). ok inoguchi@ tb@
lib/libssl/tls13_key_share.c
/* $OpenBSD: tls13_key_share.c,v 1.6 2020/04/18 14:07:56 jsing Exp $ */
/*
 * Copyright (c) 2020 Joel Sing <jsing@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <stdlib.h>

#include <openssl/curve25519.h>

#include "bytestring.h"
#include "ssl_locl.h"
#include "tls13_internal.h"

struct tls13_key_share {
	int nid;
	uint16_t group_id;

	EC_KEY *ecdhe;
	EC_KEY *ecdhe_peer;

	uint8_t *x25519_public;
	uint8_t *x25519_private;
	uint8_t *x25519_peer_public;
};

struct tls13_key_share *
tls13_key_share_new(uint16_t group_id)
{
	struct tls13_key_share *ks;
	int nid;

	if ((nid = tls1_ec_curve_id2nid(group_id)) == 0)
		return NULL;

	if ((ks = calloc(1, sizeof(struct tls13_key_share))) == NULL)
		return NULL;

	ks->group_id = group_id;
	ks->nid = nid;

	return ks;
}

struct tls13_key_share *
tls13_key_share_new_nid(int nid)
{
	uint16_t group_id;

	if ((group_id = tls1_ec_nid2curve_id(nid)) == 0)
		return NULL;

	return tls13_key_share_new(group_id);
}

void
tls13_key_share_free(struct tls13_key_share *ks)
{
	if (ks == NULL)
		return;

	EC_KEY_free(ks->ecdhe);
	EC_KEY_free(ks->ecdhe_peer);

	freezero(ks->x25519_public, X25519_KEY_LENGTH);
	freezero(ks->x25519_private, X25519_KEY_LENGTH);
	freezero(ks->x25519_peer_public, X25519_KEY_LENGTH);

	freezero(ks, sizeof(*ks));
}

uint16_t
tls13_key_share_group(struct tls13_key_share *ks)
{
	return ks->group_id;
}

int
tls13_key_share_peer_pkey(struct tls13_key_share *ks, EVP_PKEY *pkey)
{
	if (ks->nid == NID_X25519 && ks->x25519_peer_public != NULL) {
		if (!ssl_kex_dummy_ecdhe_x25519(pkey))
			return 0;
	} else if (ks->ecdhe_peer != NULL) {
		if (!EVP_PKEY_set1_EC_KEY(pkey, ks->ecdhe_peer))
			return 0;
	} else {
		return 0;
	}

	return 1;
}

static int
tls13_key_share_generate_ecdhe_ecp(struct tls13_key_share *ks)
{
	EC_KEY *ecdhe = NULL;
	int ret = 0;

	if (ks->ecdhe != NULL)
		goto err;

	if ((ecdhe = EC_KEY_new()) == NULL)
		goto err;
	if (!ssl_kex_generate_ecdhe_ecp(ecdhe, ks->nid))
		goto err;

	ks->ecdhe = ecdhe;
	ecdhe = NULL;

	ret = 1;

 err:
	EC_KEY_free(ecdhe);

	return ret;
}

static int
tls13_key_share_generate_x25519(struct tls13_key_share *ks)
{
	uint8_t *public = NULL, *private = NULL;
	int ret = 0;

	if (ks->x25519_public != NULL || ks->x25519_private != NULL)
		goto err;

	if ((public = calloc(1, X25519_KEY_LENGTH)) == NULL)
		goto err;
	if ((private = calloc(1, X25519_KEY_LENGTH)) == NULL)
		goto err;

	X25519_keypair(public, private);

	ks->x25519_public = public;
	ks->x25519_private = private;
	public = NULL;
	private = NULL;

	ret = 1;

 err:
	freezero(public, X25519_KEY_LENGTH);
	freezero(private, X25519_KEY_LENGTH);

	return ret;
}

int
tls13_key_share_generate(struct tls13_key_share *ks)
{
	if (ks->nid == NID_X25519)
		return tls13_key_share_generate_x25519(ks);

	return tls13_key_share_generate_ecdhe_ecp(ks);
}

static int
tls13_key_share_public_ecdhe_ecp(struct tls13_key_share *ks, CBB *cbb)
{
	if (ks->ecdhe == NULL)
		return 0;

	return ssl_kex_public_ecdhe_ecp(ks->ecdhe, cbb);
}

static int
tls13_key_share_public_x25519(struct tls13_key_share *ks, CBB *cbb)
{
	if (ks->x25519_public == NULL)
		return 0;

	return CBB_add_bytes(cbb, ks->x25519_public, X25519_KEY_LENGTH);
}

int
tls13_key_share_public(struct tls13_key_share *ks, CBB *cbb)
{
	CBB key_exchange;

	if (!CBB_add_u16(cbb, ks->group_id))
		goto err;
	if (!CBB_add_u16_length_prefixed(cbb, &key_exchange))
		goto err;

	if (ks->nid == NID_X25519) {
		if (!tls13_key_share_public_x25519(ks, &key_exchange))
			goto err;
	} else {
		if (!tls13_key_share_public_ecdhe_ecp(ks, &key_exchange))
			goto err;
	}

	if (!CBB_flush(cbb))
		goto err;

	return 1;

 err:
	return 0;
}

static int
tls13_key_share_peer_public_ecdhe_ecp(struct tls13_key_share *ks, CBS *cbs)
{
	EC_KEY *ecdhe = NULL;
	int ret = 0;

	if (ks->ecdhe_peer != NULL)
		goto err;

	if ((ecdhe = EC_KEY_new()) == NULL)
		goto err;
	if (!ssl_kex_peer_public_ecdhe_ecp(ecdhe, ks->nid, cbs))
		goto err;

	ks->ecdhe_peer = ecdhe;
	ecdhe = NULL;

	ret = 1;

 err:
	EC_KEY_free(ecdhe);

	return ret;
}

static int
tls13_key_share_peer_public_x25519(struct tls13_key_share *ks, CBS *cbs)
{
	size_t out_len;

	if (ks->x25519_peer_public != NULL)
		return 0;

	if (CBS_len(cbs) != X25519_KEY_LENGTH)
		return 0;

	return CBS_stow(cbs, &ks->x25519_peer_public, &out_len);
}

int
tls13_key_share_peer_public(struct tls13_key_share *ks, uint16_t group,
    CBS *cbs)
{
	if (ks->group_id != group)
		return 0;

	if (ks->nid == NID_X25519) {
		if (!tls13_key_share_peer_public_x25519(ks, cbs))
			return 0;
	} else {
		if (!tls13_key_share_peer_public_ecdhe_ecp(ks, cbs))
			return 0;
	}

	return 1;
}

static int
tls13_key_share_derive_ecdhe_ecp(struct tls13_key_share *ks,
    uint8_t **shared_key, size_t *shared_key_len)
{
	if (ks->ecdhe == NULL || ks->ecdhe_peer == NULL)
		return 0;

	return ssl_kex_derive_ecdhe_ecp(ks->ecdhe, ks->ecdhe_peer,
	    shared_key, shared_key_len);
}

static int
tls13_key_share_derive_x25519(struct tls13_key_share *ks,
    uint8_t **shared_key, size_t *shared_key_len)
{
	uint8_t *sk = NULL;
	int ret = 0;

	if (ks->x25519_private == NULL || ks->x25519_peer_public == NULL)
		goto err;

	if ((sk = calloc(1, X25519_KEY_LENGTH)) == NULL)
		goto err;
	if (!X25519(sk, ks->x25519_private, ks->x25519_peer_public))
		goto err;

	*shared_key = sk;
	*shared_key_len = X25519_KEY_LENGTH;
	sk = NULL;

	ret = 1;

 err:
	freezero(sk, X25519_KEY_LENGTH);

	return ret;
}

int
tls13_key_share_derive(struct tls13_key_share *ks, uint8_t **shared_key,
    size_t *shared_key_len)
{
	if (*shared_key != NULL)
		return 0;

	*shared_key_len = 0;

	if (ks->nid == NID_X25519)
		return tls13_key_share_derive_x25519(ks, shared_key,
		    shared_key_len);

	return tls13_key_share_derive_ecdhe_ecp(ks, shared_key,
	    shared_key_len);
}
IABSD.fr/src/lib/libssl/tls13_key_share.c

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IABSD.fr/src /lib/libssl/tls13_key_share.c
