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refactor activation of rekeying

This makes automatic rekeying internal to the packet code (previously
the server and client loops needed to assist). In doing to it makes
application of rekey limits more accurate by accounting for packets
about to be sent as well as packets queued during rekeying events
themselves.

Based on a patch from dtucker@ which was in turn based on a patch
Aleksander Adamowski in bz#2521; ok markus@

/* $OpenBSD: kex.h,v 1.76 2016/02/08 10:57:07 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 "buffer.h" /* XXX for typedef */
#include "key.h" /* XXX for typedef */

#ifdef WITH_LEAKMALLOC
#include "leakmalloc.h"
#endif

#define KEX_COOKIE_LEN	16

#define	KEX_DH1			"diffie-hellman-group1-sha1"
#define	KEX_DH14		"diffie-hellman-group14-sha1"
#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@libssh.org"

#define COMP_NONE	0
#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_GEX_SHA1,
	KEX_DH_GEX_SHA256,
	KEX_ECDH_SHA2,
	KEX_C25519_SHA256,
	KEX_MAX
};

#define KEX_INIT_SENT	0x0001

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;
	int	rsa_sha2;
	int	ext_info_c;
	struct sshbuf *my;
	struct sshbuf *peer;
	sig_atomic_t done;
	u_int	flags;
	int	hash_alg;
	int	ec_nid;
	char	*client_version_string;
	char	*server_version_string;
	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 sshkey *, struct sshkey *, u_char **, size_t *,
	    const u_char *, size_t, const char *, u_int);
	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 */
	u_char c25519_client_pubkey[CURVE25519_SIZE]; /* 25519 */
};

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

int	 kex_new(struct ssh *, char *[PROPOSAL_MAX], struct kex **);
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_send_kexinit(struct ssh *);
int	 kex_input_kexinit(int, u_int32_t, void *);
int	 kex_input_ext_info(int, u_int32_t, void *);
int	 kex_derive_keys(struct ssh *, u_char *, u_int, const struct sshbuf *);
int	 kex_derive_keys_bn(struct ssh *, u_char *, u_int, const BIGNUM *);
int	 kex_send_newkeys(struct ssh *);
int	 kex_start_rekex(struct ssh *);

int	 kexdh_client(struct ssh *);
int	 kexdh_server(struct ssh *);
int	 kexgex_client(struct ssh *);
int	 kexgex_server(struct ssh *);
int	 kexecdh_client(struct ssh *);
int	 kexecdh_server(struct ssh *);
int	 kexc25519_client(struct ssh *);
int	 kexc25519_server(struct ssh *);

int	 kex_dh_hash(const char *, const char *,
    const u_char *, size_t, const u_char *, size_t, const u_char *, size_t,
    const BIGNUM *, const BIGNUM *, const BIGNUM *, u_char *, size_t *);

int	 kexgex_hash(int, const char *, const char *,
    const u_char *, size_t, const u_char *, size_t, const u_char *, size_t,
    int, int, int,
    const BIGNUM *, const BIGNUM *, const BIGNUM *,
    const BIGNUM *, const BIGNUM *,
    u_char *, size_t *);

int kex_ecdh_hash(int, const EC_GROUP *, const char *, const char *,
    const u_char *, size_t, const u_char *, size_t, const u_char *, size_t,
    const EC_POINT *, const EC_POINT *, const BIGNUM *, u_char *, size_t *);

int	 kex_c25519_hash(int, const char *, const char *, const char *, size_t,
    const char *, size_t, const u_char *, size_t, const u_char *, const u_char *,
    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
derive_ssh1_session_id(BIGNUM *, BIGNUM *, u_int8_t[8], u_int8_t[16]);

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

#endif