/*

 * sntrup761.c - SNTRUP761x25519 ECDH functions for key exchange

 * sntrup761x25519-sha512@openssh.com - based on curve25519.c.

 *

 * This file is part of the SSH Library

 *

 * Copyright (c) 2013      by Aris Adamantiadis <aris@badcode.be>

 * Copyright (c) 2023 Simon Josefsson <simon@josefsson.org>

 * Copyright (c) 2025 Jakub Jelen <jjelen@redhat.com>

 *

 * 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, version 2.1 of the License.

 *

 * 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/sntrup761.h"

#ifdef HAVE_SNTRUP761

#include "libssh/bignum.h"

#include "libssh/buffer.h"

#include "libssh/crypto.h"

#include "libssh/dh.h"

#include "libssh/pki.h"

#include "libssh/priv.h"

#include "libssh/session.h"

#include "libssh/ssh2.h"

void crypto_hash_sha512(unsigned char *out,

                        const unsigned char *in,

                        unsigned long long inlen)

{

    sha512(in, inlen, out);

}

#ifndef HAVE_LIBGCRYPT

static void crypto_random(void *ctx, size_t length, uint8_t *dst)

{

    int *err = ctx;

    *err = ssh_get_random(dst, length, 1);

}

#endif /* HAVE_LIBGCRYPT */

static SSH_PACKET_CALLBACK(ssh_packet_client_sntrup761x25519_reply);

static ssh_packet_callback dh_client_callbacks[] = {

    ssh_packet_client_sntrup761x25519_reply,

};

static struct ssh_packet_callbacks_struct ssh_sntrup761x25519_client_callbacks =

    {

        .start = SSH2_MSG_KEX_ECDH_REPLY,

        .n_callbacks = 1,

        .callbacks = dh_client_callbacks,

        .user = NULL,

};

static int ssh_sntrup761x25519_init(ssh_session session)

{

    int rc;

    rc = ssh_curve25519_init(session);

    if (rc != SSH_OK) {

        return rc;

    }

    if (!session->server) {

#ifdef HAVE_LIBGCRYPT

        gcry_error_t err;

        err = gcry_kem_keypair(GCRY_KEM_SNTRUP761,

                               session->next_crypto->sntrup761_client_pubkey,

                               SNTRUP761_PUBLICKEY_SIZE,

                               session->next_crypto->sntrup761_privkey,

                               SNTRUP761_SECRETKEY_SIZE);

        if (err) {

            SSH_LOG(SSH_LOG_TRACE,

                    "Failed to generate sntrup761 key: %s",

                    gpg_strerror(err));

            return SSH_ERROR;

        }

#else

        sntrup761_keypair(session->next_crypto->sntrup761_client_pubkey,

                          session->next_crypto->sntrup761_privkey,

                          &rc,

                          crypto_random);

        if (rc != 1) {

            SSH_LOG(SSH_LOG_TRACE,

                    "Failed to generate sntrup761 key: PRNG failure");

            return SSH_ERROR;

        }

#endif /* HAVE_LIBGCRYPT */

    }

    return SSH_OK;

}

/** @internal

 * @brief Starts sntrup761x25519-sha512@openssh.com key exchange

 */

int ssh_client_sntrup761x25519_init(ssh_session session)

{

    int rc;

    rc = ssh_sntrup761x25519_init(session);

    if (rc != SSH_OK) {

        return rc;

    }

    rc = ssh_buffer_pack(session->out_buffer,

                         "bdPP",

                         SSH2_MSG_KEX_ECDH_INIT,

                         CURVE25519_PUBKEY_SIZE + SNTRUP761_PUBLICKEY_SIZE,

                         (size_t)SNTRUP761_PUBLICKEY_SIZE,

                         session->next_crypto->sntrup761_client_pubkey,

                         (size_t)CURVE25519_PUBKEY_SIZE,

                         session->next_crypto->curve25519_client_pubkey);

    if (rc != SSH_OK) {

        ssh_set_error_oom(session);

        return SSH_ERROR;

    }

    /* register the packet callbacks */

    ssh_packet_set_callbacks(session, &ssh_sntrup761x25519_client_callbacks);

    session->dh_handshake_state = DH_STATE_INIT_SENT;

    rc = ssh_packet_send(session);

    return rc;

}

void ssh_client_sntrup761x25519_remove_callbacks(ssh_session session)

{

    ssh_packet_remove_callbacks(session, &ssh_sntrup761x25519_client_callbacks);

}

static int ssh_sntrup761x25519_build_k(ssh_session session)

{

    unsigned char ssk[SNTRUP761_SIZE + CURVE25519_PUBKEY_SIZE];

    unsigned char *k = ssk + SNTRUP761_SIZE;

    unsigned char hss[SHA512_DIGEST_LEN];

    int rc;

    rc = ssh_curve25519_create_k(session, k);

    if (rc != SSH_OK) {

        return SSH_ERROR;

    }

#ifdef DEBUG_CRYPTO

    ssh_log_hexdump("Curve25519 shared secret", k, CURVE25519_PUBKEY_SIZE);

#endif

#ifdef HAVE_LIBGCRYPT

    if (session->server) {

        gcry_error_t err;

        err = gcry_kem_encap(GCRY_KEM_SNTRUP761,

                             session->next_crypto->sntrup761_client_pubkey,

                             SNTRUP761_PUBLICKEY_SIZE,

                             session->next_crypto->sntrup761_ciphertext,

                             SNTRUP761_CIPHERTEXT_SIZE,

                             ssk,

                             SNTRUP761_SIZE,

                             NULL,

                             0);

        if (err) {

            SSH_LOG(SSH_LOG_TRACE,

                    "Failed to encapsulate sntrup761 shared secret: %s",

                    gpg_strerror(err));

            return SSH_ERROR;

        }

    } else {

        gcry_error_t err;

        err = gcry_kem_decap(GCRY_KEM_SNTRUP761,

                             session->next_crypto->sntrup761_privkey,

                             SNTRUP761_SECRETKEY_SIZE,

                             session->next_crypto->sntrup761_ciphertext,

                             SNTRUP761_CIPHERTEXT_SIZE,

                             ssk,

                             SNTRUP761_SIZE,

                             NULL,

                             0);

        if (err) {

            SSH_LOG(SSH_LOG_TRACE,

                    "Failed to decapsulate sntrup761 shared secret: %s",

                    gpg_strerror(err));

            return SSH_ERROR;

        }

    }

#else

    if (session->server) {

        sntrup761_enc(session->next_crypto->sntrup761_ciphertext,

                      ssk,

                      session->next_crypto->sntrup761_client_pubkey,

                      &rc,

                      crypto_random);

        if (rc != 1) {

            return SSH_ERROR;

        }

    } else {

        sntrup761_dec(ssk,

                      session->next_crypto->sntrup761_ciphertext,

                      session->next_crypto->sntrup761_privkey);

    }

#endif /* HAVE_LIBGCRYPT */

#ifdef DEBUG_CRYPTO

    ssh_log_hexdump("server cipher text",

                    session->next_crypto->sntrup761_ciphertext,

                    SNTRUP761_CIPHERTEXT_SIZE);

    ssh_log_hexdump("kem key", ssk, SNTRUP761_SIZE);

#endif

    sha512(ssk, sizeof ssk, hss);

    bignum_bin2bn(hss, sizeof hss, &session->next_crypto->shared_secret);

    if (session->next_crypto->shared_secret == NULL) {

        return SSH_ERROR;

    }

#ifdef DEBUG_CRYPTO

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

#endif

    return 0;

}

/** @internal

 * @brief parses a SSH_MSG_KEX_ECDH_REPLY packet and sends back

 * a SSH_MSG_NEWKEYS

 */

static SSH_PACKET_CALLBACK(ssh_packet_client_sntrup761x25519_reply)

{

    ssh_string q_s_string = NULL;

    ssh_string pubkey_blob = NULL;

    ssh_string signature = NULL;

    int rc;

    (void)type;

    (void)user;

    ssh_client_sntrup761x25519_remove_callbacks(session);

    pubkey_blob = ssh_buffer_get_ssh_string(packet);

    if (pubkey_blob == NULL) {

        ssh_set_error(session, SSH_FATAL, "No public key in packet");

        goto error;

    }

    rc = ssh_dh_import_next_pubkey_blob(session, pubkey_blob);

    SSH_STRING_FREE(pubkey_blob);

    if (rc != 0) {

        ssh_set_error(session, SSH_FATAL, "Failed to import next public key");

        goto error;

    }

    q_s_string = ssh_buffer_get_ssh_string(packet);

    if (q_s_string == NULL) {

        ssh_set_error(session, SSH_FATAL, "No sntrup761x25519 Q_S in packet");

        goto error;

    }

    if (ssh_string_len(q_s_string) != (SNTRUP761_CIPHERTEXT_SIZE + CURVE25519_PUBKEY_SIZE)) {

        ssh_set_error(session,

                      SSH_FATAL,

                      "Incorrect size for server sntrup761x25519 ciphertext+key: %d",

                      (int)ssh_string_len(q_s_string));

        SSH_STRING_FREE(q_s_string);

        goto error;

    }

    memcpy(session->next_crypto->sntrup761_ciphertext,

           ssh_string_data(q_s_string),

           SNTRUP761_CIPHERTEXT_SIZE);

    memcpy(session->next_crypto->curve25519_server_pubkey,

           (char *)ssh_string_data(q_s_string) + SNTRUP761_CIPHERTEXT_SIZE,

           CURVE25519_PUBKEY_SIZE);

    SSH_STRING_FREE(q_s_string);

    signature = ssh_buffer_get_ssh_string(packet);

    if (signature == NULL) {

        ssh_set_error(session, SSH_FATAL, "No signature in packet");

        goto error;

    }

    session->next_crypto->dh_server_signature = signature;

    signature = NULL; /* ownership changed */

    /* TODO: verify signature now instead of waiting for NEWKEYS */

    if (ssh_sntrup761x25519_build_k(session) < 0) {

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

        goto error;

    }

    /* Send the MSG_NEWKEYS */

    if (ssh_buffer_add_u8(session->out_buffer, SSH2_MSG_NEWKEYS) < 0) {

        goto error;

    }

    rc = ssh_packet_send(session);

    if (rc == SSH_ERROR) {

        goto error;

    }

    SSH_LOG(SSH_LOG_DEBUG, "SSH_MSG_NEWKEYS sent");

    session->dh_handshake_state = DH_STATE_NEWKEYS_SENT;

    return SSH_PACKET_USED;

error:

    session->session_state = SSH_SESSION_STATE_ERROR;

    return SSH_PACKET_USED;

}

#ifdef WITH_SERVER

static SSH_PACKET_CALLBACK(ssh_packet_server_sntrup761x25519_init);

static ssh_packet_callback dh_server_callbacks[] = {

    ssh_packet_server_sntrup761x25519_init,

};

static struct ssh_packet_callbacks_struct ssh_sntrup761x25519_server_callbacks =

    {

        .start = SSH2_MSG_KEX_ECDH_INIT,

        .n_callbacks = 1,

        .callbacks = dh_server_callbacks,

        .user = NULL,

};

/** @internal

 * @brief sets up the sntrup761x25519-sha512@openssh.com kex callbacks

 */

void ssh_server_sntrup761x25519_init(ssh_session session)

{

    /* register the packet callbacks */

    ssh_packet_set_callbacks(session, &ssh_sntrup761x25519_server_callbacks);

}

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

 * SSH_MSG_KEXDH_REPLY

 */

static SSH_PACKET_CALLBACK(ssh_packet_server_sntrup761x25519_init)

{

    /* ECDH/SNTRUP761 keys */

    ssh_string q_c_string = NULL;

    ssh_string q_s_string = NULL;

    ssh_string server_pubkey_blob = NULL;

    /* SSH host keys (rsa, ed25519 and ecdsa) */

    ssh_key privkey = NULL;

    enum ssh_digest_e digest = SSH_DIGEST_AUTO;

    ssh_string sig_blob = NULL;

    int rc;

    (void)type;

    (void)user;

    ssh_packet_remove_callbacks(session, &ssh_sntrup761x25519_server_callbacks);

    /* 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 sntrup761x25519 Q_C in packet");

        goto error;

    }

    if (ssh_string_len(q_c_string) != (SNTRUP761_PUBLICKEY_SIZE + CURVE25519_PUBKEY_SIZE)) {

        ssh_set_error(session,

                      SSH_FATAL,

                      "Incorrect size for server sntrup761x25519 public key: %zu",

                      ssh_string_len(q_c_string));

        goto error;

    }

    memcpy(session->next_crypto->sntrup761_client_pubkey,

           ssh_string_data(q_c_string),

           SNTRUP761_PUBLICKEY_SIZE);

    memcpy(session->next_crypto->curve25519_client_pubkey,

           ((char *)ssh_string_data(q_c_string)) + SNTRUP761_PUBLICKEY_SIZE,

           CURVE25519_PUBKEY_SIZE);

    SSH_STRING_FREE(q_c_string);

#ifdef DEBUG_CRYPTO

    ssh_log_hexdump("client public key sntrup761",

                    session->next_crypto->sntrup761_client_pubkey,

                    SNTRUP761_PUBLICKEY_SIZE);

    ssh_log_hexdump("client public key c25519",

                    session->next_crypto->curve25519_client_pubkey,

                    CURVE25519_PUBKEY_SIZE);

#endif

    /* Build server's key pair */

    rc = ssh_sntrup761x25519_init(session);

    if (rc != SSH_OK) {

        ssh_set_error(session, SSH_FATAL, "Failed to generate sntrup761 keys");

        goto error;

    }

    rc = ssh_buffer_add_u8(session->out_buffer, SSH2_MSG_KEX_ECDH_REPLY);

    if (rc < 0) {

        ssh_set_error_oom(session);

        goto error;

    }

    /* build k and session_id */

    rc = ssh_sntrup761x25519_build_k(session);

    if (rc < 0) {

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

        goto error;

    }

    /* privkey is not allocated */

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

    if (rc == SSH_ERROR) {

        goto error;

    }

    rc = ssh_make_sessionid(session);

    if (rc != SSH_OK) {

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

        goto error;

    }

    rc = ssh_dh_get_next_server_publickey_blob(session, &server_pubkey_blob);

    if (rc != 0) {

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

        goto error;

    }

    /* add host's public key */

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

    SSH_STRING_FREE(server_pubkey_blob);

    if (rc < 0) {

        ssh_set_error_oom(session);

        goto error;

    }

    /* add ecdh public key */

    rc = ssh_buffer_add_u32(session->out_buffer,

                            ntohl(SNTRUP761_CIPHERTEXT_SIZE

                                  + CURVE25519_PUBKEY_SIZE));

    if (rc < 0) {

        ssh_set_error_oom(session);

        goto error;

    }

    rc = ssh_buffer_add_data(session->out_buffer,

                             session->next_crypto->sntrup761_ciphertext,

                             SNTRUP761_CIPHERTEXT_SIZE);

    if (rc < 0) {

        ssh_set_error_oom(session);

        goto error;

    }

    rc = ssh_buffer_add_data(session->out_buffer,

                             session->next_crypto->curve25519_server_pubkey,

                             CURVE25519_PUBKEY_SIZE);

    if (rc < 0) {

        ssh_set_error_oom(session);

        goto error;

    }

#ifdef DEBUG_CRYPTO

    ssh_log_hexdump("server public key c25519",

                    session->next_crypto->curve25519_server_pubkey,

                    CURVE25519_PUBKEY_SIZE);

#endif

    /* add signature blob */

    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");

        goto error;

    }

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

    SSH_STRING_FREE(sig_blob);

    if (rc < 0) {

        ssh_set_error_oom(session);

        goto error;

    }

#ifdef DEBUG_CRYPTO

    ssh_log_hexdump("ECDH_REPLY:",

                    ssh_buffer_get(session->out_buffer),

                    ssh_buffer_get_len(session->out_buffer));

#endif

    SSH_LOG(SSH_LOG_DEBUG, "SSH_MSG_KEX_ECDH_REPLY sent");

    rc = ssh_packet_send(session);

    if (rc == SSH_ERROR) {

        return SSH_ERROR;

    }

    /* Send the MSG_NEWKEYS */

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

    if (rc < 0) {

        goto error;

    }

    session->dh_handshake_state = DH_STATE_NEWKEYS_SENT;

    rc = ssh_packet_send(session);

    if (rc == SSH_ERROR) {

        goto error;

    }

    SSH_LOG(SSH_LOG_DEBUG, "SSH_MSG_NEWKEYS sent");

    return SSH_PACKET_USED;

error:

    SSH_STRING_FREE(q_c_string);

    SSH_STRING_FREE(q_s_string);

    ssh_buffer_reinit(session->out_buffer);

    session->session_state = SSH_SESSION_STATE_ERROR;

    return SSH_PACKET_USED;

}

#endif /* WITH_SERVER */

#endif /* HAVE_SNTRUP761 */