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1edb00c58f
openssh/kex.h
djm@openbsd.org 1edb00c58f
upstream: implement "strict key exchange" in ssh and sshd 
This adds a protocol extension to improve the integrity of the SSH
transport protocol, particular in and around the initial key exchange
(KEX) phase.

Full details of the extension are in the PROTOCOL file.

with markus@

OpenBSD-Commit-ID: 2a66ac962f0a630d7945fee54004ed9e9c439f14
2023-12-19 01:51:11 +11:00

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/* $OpenBSD: kex.h,v 1.120 2023/12/18 14:45:17 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/ecdsa.h>
# ifdef OPENSSL_HAS_ECC
# include <openssl/ec.h>
# else /* OPENSSL_HAS_ECC */
# define EC_KEY void
# define EC_GROUP void
# define EC_POINT void
# endif /* OPENSSL_HAS_ECC */
#else /* WITH_OPENSSL */
# define DH void
# define BIGNUM void
# define EC_KEY void
# define EC_GROUP void
# define EC_POINT 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
};
/* kex->flags */
#define KEX_INIT_SENT 0x0001
#define KEX_INITIAL 0x0002
#define KEX_HAS_PUBKEY_HOSTBOUND 0x0004
#define KEX_RSA_SHA2_256_SUPPORTED 0x0008 /* only set in server for now */
#define KEX_RSA_SHA2_512_SUPPORTED 0x0010 /* only set in server for now */
#define KEX_HAS_PING 0x0020
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 sshbuf;
struct kex {
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;
int kex_strict;
struct sshbuf *my;
struct sshbuf *peer;
struct sshbuf *client_version;
struct sshbuf *server_version;
struct sshbuf *session_id;
struct sshbuf *initial_sig;
struct sshkey *initial_hostkey;
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 *);
void kex_proposal_populate_entries(struct ssh *, char *prop[PROPOSAL_MAX],
const char *, const char *, const char *, const char *, const char *);
void kex_proposal_free_entries(char *prop[PROPOSAL_MAX]);
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_protocol_error(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
#if !defined(WITH_OPENSSL) || !defined(OPENSSL_HAS_ECC)
# undef EC_KEY
# undef EC_GROUP
# undef EC_POINT
#endif
#endif
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