/*

 * This file is part of the SSH Library

 *

 * Copyright (c) 2011-2013 by Aris Adamantiadis

 * Copyright (C) 2016 g10 Code GmbH

 *

 * The SSH Library is free software; you can redistribute it and/or modify

 * it under the terms of the GNU Lesser General Public License as published by

 * the Free Software Foundation; either version 2.1 of the License, or (at your

 * option) any later version.

 *

 * The SSH Library is distributed in the hope that it will be useful, but

 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY

 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public

 * License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public License

 * along with the SSH Library; see the file COPYING.  If not, write to

 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,

 * MA 02111-1307, USA.

 */

#include "config.h"

#include "libssh/session.h"

#include "libssh/ecdh.h"

#include "libssh/dh.h"

#include "libssh/buffer.h"

#include "libssh/ssh2.h"

#include "libssh/pki.h"

#include "libssh/bignum.h"

#include "libssh/libgcrypt.h"

#ifdef HAVE_ECDH

#include <gcrypt.h>

/** @internal

 * @brief Map the given key exchange enum value to its curve name.

 */

static const char *ecdh_kex_type_to_curve(enum ssh_key_exchange_e kex_type) {

    if (kex_type == SSH_KEX_ECDH_SHA2_NISTP256) {

        return "NIST P-256";

    } else if (kex_type == SSH_KEX_ECDH_SHA2_NISTP384) {

        return "NIST P-384";

    } else if (kex_type == SSH_KEX_ECDH_SHA2_NISTP521) {

        return "NIST P-521";

    }

    return NULL;

}

/** @internal

 * @brief Starts ecdh-sha2-nistp{256,384,521} key exchange.

 */

int ssh_client_ecdh_init(ssh_session session)

{

    int rc;

    gpg_error_t err;

    ssh_string client_pubkey = NULL;

    gcry_sexp_t param = NULL;

    gcry_sexp_t key = NULL;

    const char *curve = NULL;

    curve = ecdh_kex_type_to_curve(session->next_crypto->kex_type);

    if (curve == NULL) {

        rc = SSH_ERROR;

        goto out;

    }

    rc = ssh_buffer_add_u8(session->out_buffer, SSH2_MSG_KEX_ECDH_INIT);

    if (rc < 0) {

        rc = SSH_ERROR;

        goto out;

    }

    err = gcry_sexp_build(&param,

                          NULL,

                          "(genkey(ecdh(curve %s)))",

                          curve);

    if (err) {

        rc = SSH_ERROR;

        goto out;

    }

    err = gcry_pk_genkey(&key, param);

    if (err) {

        rc = SSH_ERROR;

        goto out;

    }

    client_pubkey = ssh_sexp_extract_mpi(key,

                                         "q",

                                         GCRYMPI_FMT_USG,

                                         GCRYMPI_FMT_STD);

    if (client_pubkey == NULL) {

        rc = SSH_ERROR;

        goto out;

    }

    rc = ssh_buffer_add_ssh_string(session->out_buffer, client_pubkey);

    if (rc < 0) {

        rc = SSH_ERROR;

        goto out;

    }

    session->next_crypto->ecdh_privkey = key;

    key = NULL;

    session->next_crypto->ecdh_client_pubkey = client_pubkey;

    client_pubkey = NULL;

    /* register the packet callbacks */

    ssh_packet_set_callbacks(session, &ssh_ecdh_client_callbacks);

    session->dh_handshake_state = DH_STATE_INIT_SENT;

    rc = ssh_packet_send(session);

 out:

    gcry_sexp_release(param);

    gcry_sexp_release(key);

    SSH_STRING_FREE(client_pubkey);

    return rc;

}

int ecdh_build_k(ssh_session session)

{

    gpg_error_t err;

    gcry_sexp_t data = NULL;

    gcry_sexp_t result = NULL;

    /* We need to get the x coordinate.  Libgcrypt 1.7 and above

       offers a suitable API for that.  */

#if (GCRYPT_VERSION_NUMBER >= 0x010700)

    gcry_mpi_t s = NULL;

    gcry_mpi_point_t point;

#else

    size_t k_len = 0;

    enum ssh_key_exchange_e kex_type = session->next_crypto->kex_type;

    ssh_string s;

#endif

    ssh_string pubkey_raw;

    gcry_sexp_t pubkey = NULL;

    ssh_string privkey = NULL;

    int rc = SSH_ERROR;

    const char *curve = NULL;

    curve = ecdh_kex_type_to_curve(session->next_crypto->kex_type);

    if (curve == NULL) {

        goto out;

    }

    pubkey_raw = session->server

        ? session->next_crypto->ecdh_client_pubkey

        : session->next_crypto->ecdh_server_pubkey;

    err = gcry_sexp_build(&pubkey,

                          NULL,

                          "(key-data(public-key(ecdh(curve %s)(q %b))))",

                          curve,

                          ssh_string_len(pubkey_raw),

                          ssh_string_data(pubkey_raw));

    if (err) {

        goto out;

    }

    privkey = ssh_sexp_extract_mpi(session->next_crypto->ecdh_privkey,

                                   "d",

                                   GCRYMPI_FMT_USG,

                                   GCRYMPI_FMT_STD);

    if (privkey == NULL) {

        goto out;

    }

    err = gcry_sexp_build(&data, NULL,

                          "(data(flags raw)(value %b))",

                          ssh_string_len(privkey),

                          ssh_string_data(privkey));

    if (err) {

        goto out;

    }

    err = gcry_pk_encrypt(&result, data, pubkey);

    if (err) {

        goto out;

    }

#if (GCRYPT_VERSION_NUMBER >= 0x010700)

    err = gcry_sexp_extract_param(result, "", "s", &s, NULL);

    if (err) {

        goto out;

    }

    point = gcry_mpi_point_new(0);

    if (point == NULL) {

        gcry_mpi_release(s);

        goto out;

    }

    err = gcry_mpi_ec_decode_point(point, s, NULL);

    gcry_mpi_release(s);

    if (err) {

        goto out;

    }

    session->next_crypto->shared_secret = gcry_mpi_new(0);

    gcry_mpi_point_snatch_get(session->next_crypto->shared_secret,

                              NULL, NULL, point);

#else

    s = ssh_sexp_extract_mpi(result, "s", GCRYMPI_FMT_USG, GCRYMPI_FMT_USG);

    if (s == NULL) {

        goto out;

    }

    if (kex_type == SSH_KEX_ECDH_SHA2_NISTP256) {

        k_len = 65;

    } else if (kex_type == SSH_KEX_ECDH_SHA2_NISTP384) {

        k_len = 97;

    } else if (kex_type == SSH_KEX_ECDH_SHA2_NISTP521) {

        k_len = 133;

    } else {

        ssh_string_burn(s);

        SSH_STRING_FREE(s);

        goto out;

    }

    if (ssh_string_len(s) != k_len) {

        ssh_string_burn(s);

        SSH_STRING_FREE(s);

        goto out;

    }

    err = gcry_mpi_scan(&session->next_crypto->shared_secret,

                        GCRYMPI_FMT_USG,

                        (const char *)ssh_string_data(s) + 1,

                        k_len / 2,

                        NULL);

    ssh_string_burn(s);

    SSH_STRING_FREE(s);

    if (err) {

        goto out;

    }

#endif

    rc = SSH_OK;

    gcry_sexp_release(session->next_crypto->ecdh_privkey);

    session->next_crypto->ecdh_privkey = NULL;

#ifdef DEBUG_CRYPTO

    ssh_log_hexdump("Session server cookie",

                   session->next_crypto->server_kex.cookie, 16);

    ssh_log_hexdump("Session client cookie",

                   session->next_crypto->client_kex.cookie, 16);

    ssh_print_bignum("Shared secret key", session->next_crypto->shared_secret);

#endif

 out:

    gcry_sexp_release(pubkey);

    gcry_sexp_release(data);

    gcry_sexp_release(result);

    ssh_string_burn(privkey);

    SSH_STRING_FREE(privkey);

    return rc;

}

#ifdef WITH_SERVER

/** @brief Handle a SSH_MSG_KEXDH_INIT packet (server) and send a

 * SSH_MSG_KEXDH_REPLY

 */

SSH_PACKET_CALLBACK(ssh_packet_server_ecdh_init){

    gpg_error_t err;

    /* ECDH keys */

    ssh_string q_c_string;

    ssh_string q_s_string;

    gcry_sexp_t param = NULL;

    gcry_sexp_t key = NULL;

    /* SSH host keys (rsa,dsa,ecdsa) */

    ssh_key privkey;

    enum ssh_digest_e digest = SSH_DIGEST_AUTO;

    ssh_string sig_blob = NULL;

    ssh_string pubkey_blob = NULL;

    int rc = SSH_ERROR;

    const char *curve = NULL;

    (void)type;

    (void)user;

    ssh_packet_remove_callbacks(session, &ssh_ecdh_server_callbacks);

    curve = ecdh_kex_type_to_curve(session->next_crypto->kex_type);

    if (curve == NULL) {

        goto out;

    }

    /* Extract the client pubkey from the init packet */

    q_c_string = ssh_buffer_get_ssh_string(packet);

    if (q_c_string == NULL) {

        ssh_set_error(session, SSH_FATAL, "No Q_C ECC point in packet");

        goto out;

    }

    session->next_crypto->ecdh_client_pubkey = q_c_string;

    /* Build server's keypair */

    err = gcry_sexp_build(&param, NULL, "(genkey(ecdh(curve %s) (flags transient-key)))",

                          curve);

    if (err) {

        goto out;

    }

    err = gcry_pk_genkey(&key, param);

    if (err)

        goto out;

    q_s_string = ssh_sexp_extract_mpi(key,

                                      "q",

                                      GCRYMPI_FMT_USG,

                                      GCRYMPI_FMT_STD);

    if (q_s_string == NULL) {

        goto out;

    }

    session->next_crypto->ecdh_privkey = key;

    key = NULL;

    session->next_crypto->ecdh_server_pubkey = q_s_string;

    /* build k and session_id */

    rc = ecdh_build_k(session);

    if (rc != SSH_OK) {

        ssh_set_error(session, SSH_FATAL, "Cannot build k number");

        goto out;

    }

    /* privkey is not allocated */

    rc = ssh_get_key_params(session, &privkey, &digest);

    if (rc != SSH_OK) {

        goto out;

    }

    rc = ssh_make_sessionid(session);

    if (rc != SSH_OK) {

        ssh_set_error(session, SSH_FATAL, "Could not create a session id");

        goto out;

    }

    sig_blob = ssh_srv_pki_do_sign_sessionid(session, privkey, digest);

    if (sig_blob == NULL) {

        ssh_set_error(session, SSH_FATAL, "Could not sign the session id");

        rc = SSH_ERROR;

        goto out;

    }

    rc = ssh_dh_get_next_server_publickey_blob(session, &pubkey_blob);

    if (rc != SSH_OK) {

        ssh_set_error(session, SSH_FATAL, "Could not export server public key");

        SSH_STRING_FREE(sig_blob);

        goto out;

    }

    rc = ssh_buffer_pack(session->out_buffer,

                         "bSSS",

                         SSH2_MSG_KEXDH_REPLY,

                         pubkey_blob, /* host's pubkey */

                         q_s_string, /* ecdh public key */

                         sig_blob); /* signature blob */

    SSH_STRING_FREE(sig_blob);

    SSH_STRING_FREE(pubkey_blob);

    if (rc != SSH_OK) {

        ssh_set_error_oom(session);

        goto out;

    }

    SSH_LOG(SSH_LOG_PROTOCOL, "SSH_MSG_KEXDH_REPLY sent");

    rc = ssh_packet_send(session);

    if (rc != SSH_OK) {

        goto out;

    }

    /* Send the MSG_NEWKEYS */

    rc = ssh_buffer_add_u8(session->out_buffer, SSH2_MSG_NEWKEYS);

    if (rc != SSH_OK) {

        goto out;

    }

    session->dh_handshake_state = DH_STATE_NEWKEYS_SENT;

    rc = ssh_packet_send(session);

    SSH_LOG(SSH_LOG_PROTOCOL, "SSH_MSG_NEWKEYS sent");

 out:

    gcry_sexp_release(param);

    gcry_sexp_release(key);

    if (rc == SSH_ERROR) {

        ssh_buffer_reinit(session->out_buffer);

        session->session_state = SSH_SESSION_STATE_ERROR;

    }

    return SSH_PACKET_USED;

}

#endif /* WITH_SERVER */

#endif /* HAVE_ECDH */