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Update/replace the experimental post-quantim hybrid key exchange
method based on Streamlined NTRU Prime (coupled with X25519).

The previous sntrup4591761x25519-sha512@tinyssh.org method is
replaced with sntrup761x25519-sha512@openssh.com. Per the authors,
sntrup4591761 was replaced almost two years ago by sntrup761.

The sntrup761 implementaion, like sntrup4591761 before it, is public
domain code extracted from the SUPERCOP cryptography benchmark
suite (https://bench.cr.yp.to/supercop.html).

Thanks for Daniel J Bernstein for guidance on algorithm selection.
Patch from Tobias Heider; feedback & ok markus@ and myself

(note this both the updated method and the one that it replaced are
disabled by default)

/* $OpenBSD: kex.h,v 1.112 2020/12/29 00:59:15 djm Exp $ */

/*
 * Copyright (c) 2000, 2001 Markus Friedl.  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.
 */
#ifndef KEX_H
#define KEX_H

#include "mac.h"
#include "crypto_api.h"

#ifdef WITH_OPENSSL
#include <openssl/bn.h>
#include <openssl/dh.h>
#include <openssl/ec.h>
#include <openssl/ecdsa.h>
#else /* OPENSSL */
#define BIGNUM		void
#define DH		void
#define EC_KEY		void
#define EC_GROUP	void
#endif /* WITH_OPENSSL */

#define KEX_COOKIE_LEN	16

#define	KEX_DH1				"diffie-hellman-group1-sha1"
#define	KEX_DH14_SHA1			"diffie-hellman-group14-sha1"
#define	KEX_DH14_SHA256			"diffie-hellman-group14-sha256"
#define	KEX_DH16_SHA512			"diffie-hellman-group16-sha512"
#define	KEX_DH18_SHA512			"diffie-hellman-group18-sha512"
#define	KEX_DHGEX_SHA1			"diffie-hellman-group-exchange-sha1"
#define	KEX_DHGEX_SHA256		"diffie-hellman-group-exchange-sha256"
#define	KEX_ECDH_SHA2_NISTP256		"ecdh-sha2-nistp256"
#define	KEX_ECDH_SHA2_NISTP384		"ecdh-sha2-nistp384"
#define	KEX_ECDH_SHA2_NISTP521		"ecdh-sha2-nistp521"
#define	KEX_CURVE25519_SHA256		"curve25519-sha256"
#define	KEX_CURVE25519_SHA256_OLD	"curve25519-sha256@libssh.org"
#define	KEX_SNTRUP761X25519_SHA512	"sntrup761x25519-sha512@openssh.com"

#define COMP_NONE	0
/* pre-auth compression (COMP_ZLIB) is only supported in the client */
#define COMP_ZLIB	1
#define COMP_DELAYED	2

#define CURVE25519_SIZE 32

enum kex_init_proposals {
	PROPOSAL_KEX_ALGS,
	PROPOSAL_SERVER_HOST_KEY_ALGS,
	PROPOSAL_ENC_ALGS_CTOS,
	PROPOSAL_ENC_ALGS_STOC,
	PROPOSAL_MAC_ALGS_CTOS,
	PROPOSAL_MAC_ALGS_STOC,
	PROPOSAL_COMP_ALGS_CTOS,
	PROPOSAL_COMP_ALGS_STOC,
	PROPOSAL_LANG_CTOS,
	PROPOSAL_LANG_STOC,
	PROPOSAL_MAX
};

enum kex_modes {
	MODE_IN,
	MODE_OUT,
	MODE_MAX
};

enum kex_exchange {
	KEX_DH_GRP1_SHA1,
	KEX_DH_GRP14_SHA1,
	KEX_DH_GRP14_SHA256,
	KEX_DH_GRP16_SHA512,
	KEX_DH_GRP18_SHA512,
	KEX_DH_GEX_SHA1,
	KEX_DH_GEX_SHA256,
	KEX_ECDH_SHA2,
	KEX_C25519_SHA256,
	KEX_KEM_SNTRUP761X25519_SHA512,
	KEX_MAX
};

#define KEX_INIT_SENT	0x0001
#define KEX_INITIAL	0x0002

struct sshenc {
	char	*name;
	const struct sshcipher *cipher;
	int	enabled;
	u_int	key_len;
	u_int	iv_len;
	u_int	block_size;
	u_char	*key;
	u_char	*iv;
};
struct sshcomp {
	u_int	type;
	int	enabled;
	char	*name;
};
struct newkeys {
	struct sshenc	enc;
	struct sshmac	mac;
	struct sshcomp  comp;
};

struct ssh;

struct kex {
	u_char	*session_id;
	size_t	session_id_len;
	struct newkeys	*newkeys[MODE_MAX];
	u_int	we_need;
	u_int	dh_need;
	int	server;
	char	*name;
	char	*hostkey_alg;
	int	hostkey_type;
	int	hostkey_nid;
	u_int	kex_type;
	char	*server_sig_algs;
	int	ext_info_c;
	struct sshbuf *my;
	struct sshbuf *peer;
	struct sshbuf *client_version;
	struct sshbuf *server_version;
	sig_atomic_t done;
	u_int	flags;
	int	hash_alg;
	int	ec_nid;
	char	*failed_choice;
	int	(*verify_host_key)(struct sshkey *, struct ssh *);
	struct sshkey *(*load_host_public_key)(int, int, struct ssh *);
	struct sshkey *(*load_host_private_key)(int, int, struct ssh *);
	int	(*host_key_index)(struct sshkey *, int, struct ssh *);
	int	(*sign)(struct ssh *, struct sshkey *, struct sshkey *,
	    u_char **, size_t *, const u_char *, size_t, const char *);
	int	(*kex[KEX_MAX])(struct ssh *);
	/* kex specific state */
	DH	*dh;			/* DH */
	u_int	min, max, nbits;	/* GEX */
	EC_KEY	*ec_client_key;		/* ECDH */
	const EC_GROUP *ec_group;	/* ECDH */
	u_char c25519_client_key[CURVE25519_SIZE]; /* 25519 + KEM */
	u_char c25519_client_pubkey[CURVE25519_SIZE]; /* 25519 */
	u_char sntrup761_client_key[crypto_kem_sntrup761_SECRETKEYBYTES]; /* KEM */
	struct sshbuf *client_pub;
};

int	 kex_names_valid(const char *);
char	*kex_alg_list(char);
char	*kex_names_cat(const char *, const char *);
int	 kex_assemble_names(char **, const char *, const char *);

int	 kex_exchange_identification(struct ssh *, int, const char *);

struct kex *kex_new(void);
int	 kex_ready(struct ssh *, char *[PROPOSAL_MAX]);
int	 kex_setup(struct ssh *, char *[PROPOSAL_MAX]);
void	 kex_free_newkeys(struct newkeys *);
void	 kex_free(struct kex *);

int	 kex_buf2prop(struct sshbuf *, int *, char ***);
int	 kex_prop2buf(struct sshbuf *, char *proposal[PROPOSAL_MAX]);
void	 kex_prop_free(char **);
int	 kex_load_hostkey(struct ssh *, struct sshkey **, struct sshkey **);
int	 kex_verify_host_key(struct ssh *, struct sshkey *);

int	 kex_send_kexinit(struct ssh *);
int	 kex_input_kexinit(int, u_int32_t, struct ssh *);
int	 kex_input_ext_info(int, u_int32_t, struct ssh *);
int	 kex_derive_keys(struct ssh *, u_char *, u_int, const struct sshbuf *);
int	 kex_send_newkeys(struct ssh *);
int	 kex_start_rekex(struct ssh *);

int	 kexgex_client(struct ssh *);
int	 kexgex_server(struct ssh *);
int	 kex_gen_client(struct ssh *);
int	 kex_gen_server(struct ssh *);

int	 kex_dh_keypair(struct kex *);
int	 kex_dh_enc(struct kex *, const struct sshbuf *, struct sshbuf **,
    struct sshbuf **);
int	 kex_dh_dec(struct kex *, const struct sshbuf *, struct sshbuf **);

int	 kex_ecdh_keypair(struct kex *);
int	 kex_ecdh_enc(struct kex *, const struct sshbuf *, struct sshbuf **,
    struct sshbuf **);
int	 kex_ecdh_dec(struct kex *, const struct sshbuf *, struct sshbuf **);

int	 kex_c25519_keypair(struct kex *);
int	 kex_c25519_enc(struct kex *, const struct sshbuf *, struct sshbuf **,
    struct sshbuf **);
int	 kex_c25519_dec(struct kex *, const struct sshbuf *, struct sshbuf **);

int	 kex_kem_sntrup761x25519_keypair(struct kex *);
int	 kex_kem_sntrup761x25519_enc(struct kex *, const struct sshbuf *,
    struct sshbuf **, struct sshbuf **);
int	 kex_kem_sntrup761x25519_dec(struct kex *, const struct sshbuf *,
    struct sshbuf **);

int	 kex_dh_keygen(struct kex *);
int	 kex_dh_compute_key(struct kex *, BIGNUM *, struct sshbuf *);

int	 kexgex_hash(int, const struct sshbuf *, const struct sshbuf *,
    const struct sshbuf *, const struct sshbuf *, const struct sshbuf *,
    int, int, int,
    const BIGNUM *, const BIGNUM *, const BIGNUM *,
    const BIGNUM *, const u_char *, size_t,
    u_char *, size_t *);

void	kexc25519_keygen(u_char key[CURVE25519_SIZE], u_char pub[CURVE25519_SIZE])
	__attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE)))
	__attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE)));
int	kexc25519_shared_key(const u_char key[CURVE25519_SIZE],
    const u_char pub[CURVE25519_SIZE], struct sshbuf *out)
	__attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE)))
	__attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE)));
int	kexc25519_shared_key_ext(const u_char key[CURVE25519_SIZE],
    const u_char pub[CURVE25519_SIZE], struct sshbuf *out, int)
	__attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE)))
	__attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE)));

#if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH)
void	dump_digest(const char *, const u_char *, int);
#endif

#endif