ssh-ecdsa.c

/* $OpenBSD: ssh-ecdsa.c,v 1.25 2022/10/28 00:44:44 djm Exp $ */
/*
 * Copyright (c) 2000 Markus Friedl.  All rights reserved.
 * Copyright (c) 2010 Damien Miller.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"

#if defined(WITH_OPENSSL) && defined(OPENSSL_HAS_ECC)

#include <sys/types.h>

#include <openssl/bn.h>
#include <openssl/ec.h>
#include <openssl/ecdsa.h>
#include <openssl/evp.h>

#include <string.h>

#include "sshbuf.h"
#include "ssherr.h"
#include "digest.h"
#define SSHKEY_INTERNAL
#include "sshkey.h"

#include "openbsd-compat/openssl-compat.h"

static u_int
ssh_ecdsa_size(const struct sshkey *key)
{
	switch (key->ecdsa_nid) {
	case NID_X9_62_prime256v1:
		return 256;
	case NID_secp384r1:
		return 384;
#ifdef OPENSSL_HAS_NISTP521
	case NID_secp521r1:
		return 521;
#endif
	default:
		return 0;
	}
}

static void
ssh_ecdsa_cleanup(struct sshkey *k)
{
	EC_KEY_free(k->ecdsa);
	k->ecdsa = NULL;
}

static int
ssh_ecdsa_equal(const struct sshkey *a, const struct sshkey *b)
{
	const EC_GROUP *grp_a, *grp_b;
	const EC_POINT *pub_a, *pub_b;

	if (a->ecdsa == NULL || b->ecdsa == NULL)
		return 0;
	if ((grp_a = EC_KEY_get0_group(a->ecdsa)) == NULL ||
	    (grp_b = EC_KEY_get0_group(b->ecdsa)) == NULL)
		return 0;
	if ((pub_a = EC_KEY_get0_public_key(a->ecdsa)) == NULL ||
	    (pub_b = EC_KEY_get0_public_key(b->ecdsa)) == NULL)
		return 0;
	if (EC_GROUP_cmp(grp_a, grp_b, NULL) != 0)
		return 0;
	if (EC_POINT_cmp(grp_a, pub_a, pub_b, NULL) != 0)
		return 0;

	return 1;
}

static int
ssh_ecdsa_serialize_public(const struct sshkey *key, struct sshbuf *b,
    enum sshkey_serialize_rep opts)
{
	int r;

	if (key->ecdsa == NULL)
		return SSH_ERR_INVALID_ARGUMENT;
	if ((r = sshbuf_put_cstring(b,
	    sshkey_curve_nid_to_name(key->ecdsa_nid))) != 0 ||
	    (r = sshbuf_put_eckey(b, key->ecdsa)) != 0)
		return r;

	return 0;
}

static int
ssh_ecdsa_serialize_private(const struct sshkey *key, struct sshbuf *b,
    enum sshkey_serialize_rep opts)
{
	int r;

	if (!sshkey_is_cert(key)) {
		if ((r = ssh_ecdsa_serialize_public(key, b, opts)) != 0)
			return r;
	}
	if ((r = sshbuf_put_bignum2(b,
	    EC_KEY_get0_private_key(key->ecdsa))) != 0)
		return r;
	return 0;
}

static int
ssh_ecdsa_generate(struct sshkey *k, int bits)
{
	EC_KEY *private;

	if ((k->ecdsa_nid = sshkey_ecdsa_bits_to_nid(bits)) == -1)
		return SSH_ERR_KEY_LENGTH;
	if ((private = EC_KEY_new_by_curve_name(k->ecdsa_nid)) == NULL)
		return SSH_ERR_ALLOC_FAIL;
	if (EC_KEY_generate_key(private) != 1) {
		EC_KEY_free(private);
		return SSH_ERR_LIBCRYPTO_ERROR;
	}
	EC_KEY_set_asn1_flag(private, OPENSSL_EC_NAMED_CURVE);
	k->ecdsa = private;
	return 0;
}

static int
ssh_ecdsa_copy_public(const struct sshkey *from, struct sshkey *to)
{
	to->ecdsa_nid = from->ecdsa_nid;
	if ((to->ecdsa = EC_KEY_new_by_curve_name(from->ecdsa_nid)) == NULL)
		return SSH_ERR_ALLOC_FAIL;
	if (EC_KEY_set_public_key(to->ecdsa,
	    EC_KEY_get0_public_key(from->ecdsa)) != 1)
		return SSH_ERR_LIBCRYPTO_ERROR; /* caller will free k->ecdsa */
	return 0;
}

static int
ssh_ecdsa_deserialize_public(const char *ktype, struct sshbuf *b,
    struct sshkey *key)
{
	int r;
	char *curve = NULL;

	if ((key->ecdsa_nid = sshkey_ecdsa_nid_from_name(ktype)) == -1)
		return SSH_ERR_INVALID_ARGUMENT;
	if ((r = sshbuf_get_cstring(b, &curve, NULL)) != 0)
		goto out;
	if (key->ecdsa_nid != sshkey_curve_name_to_nid(curve)) {
		r = SSH_ERR_EC_CURVE_MISMATCH;
		goto out;
	}
	EC_KEY_free(key->ecdsa);
	key->ecdsa = NULL;
	if ((key->ecdsa = EC_KEY_new_by_curve_name(key->ecdsa_nid)) == NULL) {
		r = SSH_ERR_LIBCRYPTO_ERROR;
		goto out;
	}
	if ((r = sshbuf_get_eckey(b, key->ecdsa)) != 0)
		goto out;
	if (sshkey_ec_validate_public(EC_KEY_get0_group(key->ecdsa),
	    EC_KEY_get0_public_key(key->ecdsa)) != 0) {
		r = SSH_ERR_KEY_INVALID_EC_VALUE;
		goto out;
	}
	/* success */
	r = 0;
#ifdef DEBUG_PK
	sshkey_dump_ec_point(EC_KEY_get0_group(key->ecdsa),
	    EC_KEY_get0_public_key(key->ecdsa));
#endif
 out:
	free(curve);
	if (r != 0) {
		EC_KEY_free(key->ecdsa);
		key->ecdsa = NULL;
	}
	return r;
}

static int
ssh_ecdsa_deserialize_private(const char *ktype, struct sshbuf *b,
    struct sshkey *key)
{
	int r;
	BIGNUM *exponent = NULL;

	if (!sshkey_is_cert(key)) {
		if ((r = ssh_ecdsa_deserialize_public(ktype, b, key)) != 0)
			return r;
	}
	if ((r = sshbuf_get_bignum2(b, &exponent)) != 0)
		goto out;
	if (EC_KEY_set_private_key(key->ecdsa, exponent) != 1) {
		r = SSH_ERR_LIBCRYPTO_ERROR;
		goto out;
	}
	if ((r = sshkey_ec_validate_private(key->ecdsa)) != 0)
		goto out;
	/* success */
	r = 0;
 out:
	BN_clear_free(exponent);
	return r;
}

/* ARGSUSED */
static int
ssh_ecdsa_sign(struct sshkey *key,
    u_char **sigp, size_t *lenp,
    const u_char *data, size_t dlen,
    const char *alg, const char *sk_provider, const char *sk_pin, u_int compat)
{
	ECDSA_SIG *esig = NULL;
	const BIGNUM *sig_r, *sig_s;
	int hash_alg;
	u_char digest[SSH_DIGEST_MAX_LENGTH];
	size_t len, hlen;
	struct sshbuf *b = NULL, *bb = NULL;
	int ret = SSH_ERR_INTERNAL_ERROR;

	if (lenp != NULL)
		*lenp = 0;
	if (sigp != NULL)
		*sigp = NULL;

	if (key == NULL || key->ecdsa == NULL ||
	    sshkey_type_plain(key->type) != KEY_ECDSA)
		return SSH_ERR_INVALID_ARGUMENT;

	if ((hash_alg = sshkey_ec_nid_to_hash_alg(key->ecdsa_nid)) == -1 ||
	    (hlen = ssh_digest_bytes(hash_alg)) == 0)
		return SSH_ERR_INTERNAL_ERROR;
	if ((ret = ssh_digest_memory(hash_alg, data, dlen,
	    digest, sizeof(digest))) != 0)
		goto out;

	if ((esig = ECDSA_do_sign(digest, hlen, key->ecdsa)) == NULL) {
		ret = SSH_ERR_LIBCRYPTO_ERROR;
		goto out;
	}

	if ((bb = sshbuf_new()) == NULL || (b = sshbuf_new()) == NULL) {
		ret = SSH_ERR_ALLOC_FAIL;
		goto out;
	}
	ECDSA_SIG_get0(esig, &sig_r, &sig_s);
	if ((ret = sshbuf_put_bignum2(bb, sig_r)) != 0 ||
	    (ret = sshbuf_put_bignum2(bb, sig_s)) != 0)
		goto out;
	if ((ret = sshbuf_put_cstring(b, sshkey_ssh_name_plain(key))) != 0 ||
	    (ret = sshbuf_put_stringb(b, bb)) != 0)
		goto out;
	len = sshbuf_len(b);
	if (sigp != NULL) {
		if ((*sigp = malloc(len)) == NULL) {
			ret = SSH_ERR_ALLOC_FAIL;
			goto out;
		}
		memcpy(*sigp, sshbuf_ptr(b), len);
	}
	if (lenp != NULL)
		*lenp = len;
	ret = 0;
 out:
	explicit_bzero(digest, sizeof(digest));
	sshbuf_free(b);
	sshbuf_free(bb);
	ECDSA_SIG_free(esig);
	return ret;
}

/* ARGSUSED */
static int
ssh_ecdsa_verify(const struct sshkey *key,
    const u_char *sig, size_t siglen,
    const u_char *data, size_t dlen, const char *alg, u_int compat,
    struct sshkey_sig_details **detailsp)
{
	ECDSA_SIG *esig = NULL;
	BIGNUM *sig_r = NULL, *sig_s = NULL;
	int hash_alg;
	u_char digest[SSH_DIGEST_MAX_LENGTH];
	size_t hlen;
	int ret = SSH_ERR_INTERNAL_ERROR;
	struct sshbuf *b = NULL, *sigbuf = NULL;
	char *ktype = NULL;

	if (key == NULL || key->ecdsa == NULL ||
	    sshkey_type_plain(key->type) != KEY_ECDSA ||
	    sig == NULL || siglen == 0)
		return SSH_ERR_INVALID_ARGUMENT;

	if ((hash_alg = sshkey_ec_nid_to_hash_alg(key->ecdsa_nid)) == -1 ||
	    (hlen = ssh_digest_bytes(hash_alg)) == 0)
		return SSH_ERR_INTERNAL_ERROR;

	/* fetch signature */
	if ((b = sshbuf_from(sig, siglen)) == NULL)
		return SSH_ERR_ALLOC_FAIL;
	if (sshbuf_get_cstring(b, &ktype, NULL) != 0 ||
	    sshbuf_froms(b, &sigbuf) != 0) {
		ret = SSH_ERR_INVALID_FORMAT;
		goto out;
	}
	if (strcmp(sshkey_ssh_name_plain(key), ktype) != 0) {
		ret = SSH_ERR_KEY_TYPE_MISMATCH;
		goto out;
	}
	if (sshbuf_len(b) != 0) {
		ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
		goto out;
	}

	/* parse signature */
	if (sshbuf_get_bignum2(sigbuf, &sig_r) != 0 ||
	    sshbuf_get_bignum2(sigbuf, &sig_s) != 0) {
		ret = SSH_ERR_INVALID_FORMAT;
		goto out;
	}
	if ((esig = ECDSA_SIG_new()) == NULL) {
		ret = SSH_ERR_ALLOC_FAIL;
		goto out;
	}
	if (!ECDSA_SIG_set0(esig, sig_r, sig_s)) {
		ret = SSH_ERR_LIBCRYPTO_ERROR;
		goto out;
	}
	sig_r = sig_s = NULL; /* transferred */

	if (sshbuf_len(sigbuf) != 0) {
		ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
		goto out;
	}
	if ((ret = ssh_digest_memory(hash_alg, data, dlen,
	    digest, sizeof(digest))) != 0)
		goto out;

	switch (ECDSA_do_verify(digest, hlen, esig, key->ecdsa)) {
	case 1:
		ret = 0;
		break;
	case 0:
		ret = SSH_ERR_SIGNATURE_INVALID;
		goto out;
	default:
		ret = SSH_ERR_LIBCRYPTO_ERROR;
		goto out;
	}

 out:
	explicit_bzero(digest, sizeof(digest));
	sshbuf_free(sigbuf);
	sshbuf_free(b);
	ECDSA_SIG_free(esig);
	BN_clear_free(sig_r);
	BN_clear_free(sig_s);
	free(ktype);
	return ret;
}

/* NB. not static; used by ECDSA-SK */
const struct sshkey_impl_funcs sshkey_ecdsa_funcs = {
	/* .size = */		ssh_ecdsa_size,
	/* .alloc = */		NULL,
	/* .cleanup = */	ssh_ecdsa_cleanup,
	/* .equal = */		ssh_ecdsa_equal,
	/* .ssh_serialize_public = */ ssh_ecdsa_serialize_public,
	/* .ssh_deserialize_public = */ ssh_ecdsa_deserialize_public,
	/* .ssh_serialize_private = */ ssh_ecdsa_serialize_private,
	/* .ssh_deserialize_private = */ ssh_ecdsa_deserialize_private,
	/* .generate = */	ssh_ecdsa_generate,
	/* .copy_public = */	ssh_ecdsa_copy_public,
	/* .sign = */		ssh_ecdsa_sign,
	/* .verify = */		ssh_ecdsa_verify,
};

const struct sshkey_impl sshkey_ecdsa_nistp256_impl = {
	/* .name = */		"ecdsa-sha2-nistp256",
	/* .shortname = */	"ECDSA",
	/* .sigalg = */		NULL,
	/* .type = */		KEY_ECDSA,
	/* .nid = */		NID_X9_62_prime256v1,
	/* .cert = */		0,
	/* .sigonly = */	0,
	/* .keybits = */	0,
	/* .funcs = */		&sshkey_ecdsa_funcs,
};

const struct sshkey_impl sshkey_ecdsa_nistp256_cert_impl = {
	/* .name = */		"ecdsa-sha2-nistp256-cert-v01@openssh.com",
	/* .shortname = */	"ECDSA-CERT",
	/* .sigalg = */		NULL,
	/* .type = */		KEY_ECDSA_CERT,
	/* .nid = */		NID_X9_62_prime256v1,
	/* .cert = */		1,
	/* .sigonly = */	0,
	/* .keybits = */	0,
	/* .funcs = */		&sshkey_ecdsa_funcs,
};

const struct sshkey_impl sshkey_ecdsa_nistp384_impl = {
	/* .name = */		"ecdsa-sha2-nistp384",
	/* .shortname = */	"ECDSA",
	/* .sigalg = */		NULL,
	/* .type = */		KEY_ECDSA,
	/* .nid = */		NID_secp384r1,
	/* .cert = */		0,
	/* .sigonly = */	0,
	/* .keybits = */	0,
	/* .funcs = */		&sshkey_ecdsa_funcs,
};

const struct sshkey_impl sshkey_ecdsa_nistp384_cert_impl = {
	/* .name = */		"ecdsa-sha2-nistp384-cert-v01@openssh.com",
	/* .shortname = */	"ECDSA-CERT",
	/* .sigalg = */		NULL,
	/* .type = */		KEY_ECDSA_CERT,
	/* .nid = */		NID_secp384r1,
	/* .cert = */		1,
	/* .sigonly = */	0,
	/* .keybits = */	0,
	/* .funcs = */		&sshkey_ecdsa_funcs,
};

#ifdef OPENSSL_HAS_NISTP521
const struct sshkey_impl sshkey_ecdsa_nistp521_impl = {
	/* .name = */		"ecdsa-sha2-nistp521",
	/* .shortname = */	"ECDSA",
	/* .sigalg = */		NULL,
	/* .type = */		KEY_ECDSA,
	/* .nid = */		NID_secp521r1,
	/* .cert = */		0,
	/* .sigonly = */	0,
	/* .keybits = */	0,
	/* .funcs = */		&sshkey_ecdsa_funcs,
};

const struct sshkey_impl sshkey_ecdsa_nistp521_cert_impl = {
	/* .name = */		"ecdsa-sha2-nistp521-cert-v01@openssh.com",
	/* .shortname = */	"ECDSA-CERT",
	/* .sigalg = */		NULL,
	/* .type = */		KEY_ECDSA_CERT,
	/* .nid = */		NID_secp521r1,
	/* .cert = */		1,
	/* .sigonly = */	0,
	/* .keybits = */	0,
	/* .funcs = */		&sshkey_ecdsa_funcs,
};
#endif

#endif /* WITH_OPENSSL && OPENSSL_HAS_ECC */