/* $OpenBSD: kex.h,v 1.129 2026/03/05 05:40:36 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"
#define KEX_SNTRUP761X25519_SHA512_OLD  "sntrup761x25519-sha512@openssh.com"
#define KEX_MLKEM768X25519_SHA256       "mlkem768x25519-sha256"

#define COMP_NONE       0
#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 = 1,
        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_KEM_MLKEM768X25519_SHA256,
        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
#define KEX_HAS_EXT_INFO_IN_AUTH        0x0040
#define KEX_HAS_NEWAGENT                0x0080 /* only set in client */

/* kex->pq */
#define KEX_NOT_PQ                      0
#define KEX_IS_PQ                       1

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     ext_info_s;
        int     kex_strict;
        int     ext_info_received;
        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 */
        u_char mlkem768_client_key[crypto_kem_mlkem768_SECRETKEYBYTES]; /* KEM */
        struct sshbuf *client_pub;
};

int      kex_name_valid(const char *);
u_int    kex_type_from_name(const char *);
int      kex_hash_from_name(const char *);
int      kex_nid_from_name(const char *);
int      kex_is_pq_from_name(const char *);
int      kex_names_valid(const char *);
char    *kex_alg_list(char);
char    *kex_names_cat(const char *, const char *);
int      kex_has_any_alg(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, uint32_t, struct ssh *);
int      kex_input_ext_info(int, uint32_t, struct ssh *);
int      kex_protocol_error(int, uint32_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      kex_server_update_ext_info(struct ssh *);
void     kex_set_server_sig_algs(struct ssh *, const char *);

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_kem_mlkem768x25519_keypair(struct kex *);
int      kex_kem_mlkem768x25519_enc(struct kex *, const struct sshbuf *,
    struct sshbuf **, struct sshbuf **);
int      kex_kem_mlkem768x25519_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