libzmq/src/curve_server.cpp

/* SPDX-License-Identifier: MPL-2.0 */

#include "precompiled.hpp"
#include "macros.hpp"

#ifdef ZMQ_HAVE_CURVE

#include "msg.hpp"
#include "session_base.hpp"
#include "err.hpp"
#include "curve_server.hpp"
#include "wire.hpp"
#include "secure_allocator.hpp"

zmq::curve_server_t::curve_server_t (session_base_t *session_,
                                     const std::string &peer_address_,
                                     const options_t &options_,
                                     const bool downgrade_sub_) :
    mechanism_base_t (session_, options_),
    zap_client_common_handshake_t (
      session_, peer_address_, options_, sending_ready),
    curve_mechanism_base_t (session_,
                            options_,
                            "CurveZMQMESSAGES",
                            "CurveZMQMESSAGEC",
                            downgrade_sub_)
{
    int rc;
    //  Fetch our secret key from socket options
    memcpy (_secret_key, options_.curve_secret_key, crypto_box_SECRETKEYBYTES);

    //  Generate short-term key pair
    memset (_cn_secret, 0, crypto_box_SECRETKEYBYTES);
    memset (_cn_public, 0, crypto_box_PUBLICKEYBYTES);
    rc = crypto_box_keypair (_cn_public, _cn_secret);
    zmq_assert (rc == 0);
}

zmq::curve_server_t::~curve_server_t ()
{
}

int zmq::curve_server_t::next_handshake_command (msg_t *msg_)
{
    int rc = 0;

    switch (state) {
        case sending_welcome:
            rc = produce_welcome (msg_);
            if (rc == 0)
                state = waiting_for_initiate;
            break;
        case sending_ready:
            rc = produce_ready (msg_);
            if (rc == 0)
                state = ready;
            break;
        case sending_error:
            rc = produce_error (msg_);
            if (rc == 0)
                state = error_sent;
            break;
        default:
            errno = EAGAIN;
            rc = -1;
            break;
    }
    return rc;
}

int zmq::curve_server_t::process_handshake_command (msg_t *msg_)
{
    int rc = 0;

    switch (state) {
        case waiting_for_hello:
            rc = process_hello (msg_);
            break;
        case waiting_for_initiate:
            rc = process_initiate (msg_);
            break;
        default:
            // TODO I think this is not a case reachable with a misbehaving
            // client. It is not an "invalid handshake command", but would be
            // trying to process a handshake command in an invalid state,
            // which is purely under control of this peer.
            // Therefore, it should be changed to zmq_assert (false);

            // CURVE I: invalid handshake command
            session->get_socket ()->event_handshake_failed_protocol (
              session->get_endpoint (), ZMQ_PROTOCOL_ERROR_ZMTP_UNSPECIFIED);
            errno = EPROTO;
            rc = -1;
            break;
    }
    if (rc == 0) {
        rc = msg_->close ();
        errno_assert (rc == 0);
        rc = msg_->init ();
        errno_assert (rc == 0);
    }
    return rc;
}

int zmq::curve_server_t::encode (msg_t *msg_)
{
    zmq_assert (state == ready);
    return curve_mechanism_base_t::encode (msg_);
}

int zmq::curve_server_t::decode (msg_t *msg_)
{
    zmq_assert (state == ready);
    return curve_mechanism_base_t::decode (msg_);
}

int zmq::curve_server_t::process_hello (msg_t *msg_)
{
    int rc = check_basic_command_structure (msg_);
    if (rc == -1)
        return -1;

    const size_t size = msg_->size ();
    const uint8_t *const hello = static_cast<uint8_t *> (msg_->data ());

    if (size < 6 || memcmp (hello, "\x05HELLO", 6)) {
        session->get_socket ()->event_handshake_failed_protocol (
          session->get_endpoint (), ZMQ_PROTOCOL_ERROR_ZMTP_UNEXPECTED_COMMAND);
        errno = EPROTO;
        return -1;
    }

    if (size != 200) {
        session->get_socket ()->event_handshake_failed_protocol (
          session->get_endpoint (),
          ZMQ_PROTOCOL_ERROR_ZMTP_MALFORMED_COMMAND_HELLO);
        errno = EPROTO;
        return -1;
    }

    const uint8_t major = hello[6];
    const uint8_t minor = hello[7];

    if (major != 1 || minor != 0) {
        // CURVE I: client HELLO has unknown version number
        session->get_socket ()->event_handshake_failed_protocol (
          session->get_endpoint (),
          ZMQ_PROTOCOL_ERROR_ZMTP_MALFORMED_COMMAND_HELLO);
        errno = EPROTO;
        return -1;
    }

    //  Save client's short-term public key (C')
    memcpy (_cn_client, hello + 80, 32);

    uint8_t hello_nonce[crypto_box_NONCEBYTES];
    std::vector<uint8_t, secure_allocator_t<uint8_t> > hello_plaintext (
      crypto_box_ZEROBYTES + 64);
    uint8_t hello_box[crypto_box_BOXZEROBYTES + 80];

    memcpy (hello_nonce, "CurveZMQHELLO---", 16);
    memcpy (hello_nonce + 16, hello + 112, 8);
    set_peer_nonce (get_uint64 (hello + 112));

    memset (hello_box, 0, crypto_box_BOXZEROBYTES);
    memcpy (hello_box + crypto_box_BOXZEROBYTES, hello + 120, 80);

    //  Open Box [64 * %x0](C'->S)
    rc = crypto_box_open (&hello_plaintext[0], hello_box, sizeof hello_box,
                          hello_nonce, _cn_client, _secret_key);
    if (rc != 0) {
        // CURVE I: cannot open client HELLO -- wrong server key?
        session->get_socket ()->event_handshake_failed_protocol (
          session->get_endpoint (), ZMQ_PROTOCOL_ERROR_ZMTP_CRYPTOGRAPHIC);
        errno = EPROTO;
        return -1;
    }

    state = sending_welcome;
    return rc;
}

int zmq::curve_server_t::produce_welcome (msg_t *msg_)
{
    uint8_t cookie_nonce[crypto_secretbox_NONCEBYTES];
    std::vector<uint8_t, secure_allocator_t<uint8_t> > cookie_plaintext (
      crypto_secretbox_ZEROBYTES + 64);
    uint8_t cookie_ciphertext[crypto_secretbox_BOXZEROBYTES + 80];

    //  Create full nonce for encryption
    //  8-byte prefix plus 16-byte random nonce
    memset (cookie_nonce, 0, crypto_secretbox_NONCEBYTES);
    memcpy (cookie_nonce, "COOKIE--", 8);
    randombytes (cookie_nonce + 8, 16);

    //  Generate cookie = Box [C' + s'](t)
    std::fill (cookie_plaintext.begin (),
               cookie_plaintext.begin () + crypto_secretbox_ZEROBYTES, 0);
    memcpy (&cookie_plaintext[crypto_secretbox_ZEROBYTES], _cn_client, 32);
    memcpy (&cookie_plaintext[crypto_secretbox_ZEROBYTES + 32], _cn_secret, 32);

    //  Generate fresh cookie key
    memset (_cookie_key, 0, crypto_secretbox_KEYBYTES);
    randombytes (_cookie_key, crypto_secretbox_KEYBYTES);

    //  Encrypt using symmetric cookie key
    int rc =
      crypto_secretbox (cookie_ciphertext, &cookie_plaintext[0],
                        cookie_plaintext.size (), cookie_nonce, _cookie_key);
    zmq_assert (rc == 0);

    uint8_t welcome_nonce[crypto_box_NONCEBYTES];
    std::vector<uint8_t, secure_allocator_t<uint8_t> > welcome_plaintext (
      crypto_box_ZEROBYTES + 128);
    uint8_t welcome_ciphertext[crypto_box_BOXZEROBYTES + 144];

    //  Create full nonce for encryption
    //  8-byte prefix plus 16-byte random nonce
    memset (welcome_nonce, 0, crypto_box_NONCEBYTES);
    memcpy (welcome_nonce, "WELCOME-", 8);
    randombytes (welcome_nonce + 8, crypto_box_NONCEBYTES - 8);

    //  Create 144-byte Box [S' + cookie](S->C')
    std::fill (welcome_plaintext.begin (),
               welcome_plaintext.begin () + crypto_box_ZEROBYTES, 0);
    memcpy (&welcome_plaintext[crypto_box_ZEROBYTES], _cn_public, 32);
    memcpy (&welcome_plaintext[crypto_box_ZEROBYTES + 32], cookie_nonce + 8,
            16);
    memcpy (&welcome_plaintext[crypto_box_ZEROBYTES + 48],
            cookie_ciphertext + crypto_secretbox_BOXZEROBYTES, 80);

    rc = crypto_box (welcome_ciphertext, &welcome_plaintext[0],
                     welcome_plaintext.size (), welcome_nonce, _cn_client,
                     _secret_key);

    //  TODO I think we should change this back to zmq_assert (rc == 0);
    //  as it was before https://github.com/zeromq/libzmq/pull/1832
    //  The reason given there was that secret_key might be 0ed.
    //  But if it were, we would never get this far, since we could
    //  not have opened the client's hello box with a 0ed key.

    if (rc == -1)
        return -1;

    rc = msg_->init_size (168);
    errno_assert (rc == 0);

    uint8_t *const welcome = static_cast<uint8_t *> (msg_->data ());
    memcpy (welcome, "\x07WELCOME", 8);
    memcpy (welcome + 8, welcome_nonce + 8, 16);
    memcpy (welcome + 24, welcome_ciphertext + crypto_box_BOXZEROBYTES, 144);

    return 0;
}

int zmq::curve_server_t::process_initiate (msg_t *msg_)
{
    int rc = check_basic_command_structure (msg_);
    if (rc == -1)
        return -1;

    const size_t size = msg_->size ();
    const uint8_t *initiate = static_cast<uint8_t *> (msg_->data ());

    if (size < 9 || memcmp (initiate, "\x08INITIATE", 9)) {
        session->get_socket ()->event_handshake_failed_protocol (
          session->get_endpoint (), ZMQ_PROTOCOL_ERROR_ZMTP_UNEXPECTED_COMMAND);
        errno = EPROTO;
        return -1;
    }

    if (size < 257) {
        session->get_socket ()->event_handshake_failed_protocol (
          session->get_endpoint (),
          ZMQ_PROTOCOL_ERROR_ZMTP_MALFORMED_COMMAND_INITIATE);
        errno = EPROTO;
        return -1;
    }

    uint8_t cookie_nonce[crypto_secretbox_NONCEBYTES];
    uint8_t cookie_plaintext[crypto_secretbox_ZEROBYTES + 64];
    uint8_t cookie_box[crypto_secretbox_BOXZEROBYTES + 80];

    //  Open Box [C' + s'](t)
    memset (cookie_box, 0, crypto_secretbox_BOXZEROBYTES);
    memcpy (cookie_box + crypto_secretbox_BOXZEROBYTES, initiate + 25, 80);

    memcpy (cookie_nonce, "COOKIE--", 8);
    memcpy (cookie_nonce + 8, initiate + 9, 16);

    rc = crypto_secretbox_open (cookie_plaintext, cookie_box, sizeof cookie_box,
                                cookie_nonce, _cookie_key);
    if (rc != 0) {
        // CURVE I: cannot open client INITIATE cookie
        session->get_socket ()->event_handshake_failed_protocol (
          session->get_endpoint (), ZMQ_PROTOCOL_ERROR_ZMTP_CRYPTOGRAPHIC);
        errno = EPROTO;
        return -1;
    }

    //  Check cookie plain text is as expected [C' + s']
    if (memcmp (cookie_plaintext + crypto_secretbox_ZEROBYTES, _cn_client, 32)
        || memcmp (cookie_plaintext + crypto_secretbox_ZEROBYTES + 32,
                   _cn_secret, 32)) {
        // TODO this case is very hard to test, as it would require a modified
        //  client that knows the server's secret temporary cookie key

        // CURVE I: client INITIATE cookie is not valid
        session->get_socket ()->event_handshake_failed_protocol (
          session->get_endpoint (), ZMQ_PROTOCOL_ERROR_ZMTP_CRYPTOGRAPHIC);
        errno = EPROTO;
        return -1;
    }

    const size_t clen = (size - 113) + crypto_box_BOXZEROBYTES;

    uint8_t initiate_nonce[crypto_box_NONCEBYTES];
    std::vector<uint8_t, secure_allocator_t<uint8_t> > initiate_plaintext (
      crypto_box_ZEROBYTES + clen);
    std::vector<uint8_t> initiate_box (crypto_box_BOXZEROBYTES + clen);

    //  Open Box [C + vouch + metadata](C'->S')
    std::fill (initiate_box.begin (),
               initiate_box.begin () + crypto_box_BOXZEROBYTES, 0);
    memcpy (&initiate_box[crypto_box_BOXZEROBYTES], initiate + 113,
            clen - crypto_box_BOXZEROBYTES);

    memcpy (initiate_nonce, "CurveZMQINITIATE", 16);
    memcpy (initiate_nonce + 16, initiate + 105, 8);
    set_peer_nonce (get_uint64 (initiate + 105));

    const uint8_t *client_key = &initiate_plaintext[crypto_box_ZEROBYTES];

    rc = crypto_box_open (&initiate_plaintext[0], &initiate_box[0], clen,
                          initiate_nonce, _cn_client, _cn_secret);
    if (rc != 0) {
        // CURVE I: cannot open client INITIATE
        session->get_socket ()->event_handshake_failed_protocol (
          session->get_endpoint (), ZMQ_PROTOCOL_ERROR_ZMTP_CRYPTOGRAPHIC);
        errno = EPROTO;
        return -1;
    }

    uint8_t vouch_nonce[crypto_box_NONCEBYTES];
    std::vector<uint8_t, secure_allocator_t<uint8_t> > vouch_plaintext (
      crypto_box_ZEROBYTES + 64);
    uint8_t vouch_box[crypto_box_BOXZEROBYTES + 80];

    //  Open Box Box [C',S](C->S') and check contents
    memset (vouch_box, 0, crypto_box_BOXZEROBYTES);
    memcpy (vouch_box + crypto_box_BOXZEROBYTES,
            &initiate_plaintext[crypto_box_ZEROBYTES + 48], 80);

    memset (vouch_nonce, 0, crypto_box_NONCEBYTES);
    memcpy (vouch_nonce, "VOUCH---", 8);
    memcpy (vouch_nonce + 8, &initiate_plaintext[crypto_box_ZEROBYTES + 32],
            16);

    rc = crypto_box_open (&vouch_plaintext[0], vouch_box, sizeof vouch_box,
                          vouch_nonce, client_key, _cn_secret);
    if (rc != 0) {
        // CURVE I: cannot open client INITIATE vouch
        session->get_socket ()->event_handshake_failed_protocol (
          session->get_endpoint (), ZMQ_PROTOCOL_ERROR_ZMTP_CRYPTOGRAPHIC);
        errno = EPROTO;
        return -1;
    }

    //  What we decrypted must be the client's short-term public key
    if (memcmp (&vouch_plaintext[crypto_box_ZEROBYTES], _cn_client, 32)) {
        // TODO this case is very hard to test, as it would require a modified
        //  client that knows the server's secret short-term key

        // CURVE I: invalid handshake from client (public key)
        session->get_socket ()->event_handshake_failed_protocol (
          session->get_endpoint (), ZMQ_PROTOCOL_ERROR_ZMTP_KEY_EXCHANGE);
        errno = EPROTO;
        return -1;
    }

    //  Precompute connection secret from client key
    rc = crypto_box_beforenm (get_writable_precom_buffer (), _cn_client,
                              _cn_secret);
    zmq_assert (rc == 0);

    //  Given this is a backward-incompatible change, it's behind a socket
    //  option disabled by default.
    if (zap_required () || !options.zap_enforce_domain) {
        //  Use ZAP protocol (RFC 27) to authenticate the user.
        rc = session->zap_connect ();
        if (rc == 0) {
            send_zap_request (client_key);
            state = waiting_for_zap_reply;

            //  TODO actually, it is quite unlikely that we can read the ZAP
            //  reply already, but removing this has some strange side-effect
            //  (probably because the pipe's in_active flag is true until a read
            //  is attempted)
            if (-1 == receive_and_process_zap_reply ())
                return -1;
        } else if (!options.zap_enforce_domain) {
            //  This supports the Stonehouse pattern (encryption without
            //  authentication) in legacy mode (domain set but no handler).
            state = sending_ready;
        } else {
            session->get_socket ()->event_handshake_failed_no_detail (
              session->get_endpoint (), EFAULT);
            return -1;
        }
    } else {
        //  This supports the Stonehouse pattern (encryption without authentication).
        state = sending_ready;
    }

    return parse_metadata (&initiate_plaintext[crypto_box_ZEROBYTES + 128],
                           clen - crypto_box_ZEROBYTES - 128);
}

int zmq::curve_server_t::produce_ready (msg_t *msg_)
{
    const size_t metadata_length = basic_properties_len ();
    uint8_t ready_nonce[crypto_box_NONCEBYTES];

    std::vector<uint8_t, secure_allocator_t<uint8_t> > ready_plaintext (
      crypto_box_ZEROBYTES + metadata_length);

    //  Create Box [metadata](S'->C')
    std::fill (ready_plaintext.begin (),
               ready_plaintext.begin () + crypto_box_ZEROBYTES, 0);
    uint8_t *ptr = &ready_plaintext[crypto_box_ZEROBYTES];

    ptr += add_basic_properties (ptr, metadata_length);
    const size_t mlen = ptr - &ready_plaintext[0];

    memcpy (ready_nonce, "CurveZMQREADY---", 16);
    put_uint64 (ready_nonce + 16, get_and_inc_nonce ());

    std::vector<uint8_t> ready_box (crypto_box_BOXZEROBYTES + 16
                                    + metadata_length);

    int rc = crypto_box_afternm (&ready_box[0], &ready_plaintext[0], mlen,
                                 ready_nonce, get_precom_buffer ());
    zmq_assert (rc == 0);

    rc = msg_->init_size (14 + mlen - crypto_box_BOXZEROBYTES);
    errno_assert (rc == 0);

    uint8_t *ready = static_cast<uint8_t *> (msg_->data ());

    memcpy (ready, "\x05READY", 6);
    //  Short nonce, prefixed by "CurveZMQREADY---"
    memcpy (ready + 6, ready_nonce + 16, 8);
    //  Box [metadata](S'->C')
    memcpy (ready + 14, &ready_box[crypto_box_BOXZEROBYTES],
            mlen - crypto_box_BOXZEROBYTES);

    return 0;
}

int zmq::curve_server_t::produce_error (msg_t *msg_) const
{
    const size_t expected_status_code_length = 3;
    zmq_assert (status_code.length () == 3);
    const int rc = msg_->init_size (6 + 1 + expected_status_code_length);
    zmq_assert (rc == 0);
    char *msg_data = static_cast<char *> (msg_->data ());
    memcpy (msg_data, "\5ERROR", 6);
    msg_data[6] = expected_status_code_length;
    memcpy (msg_data + 7, status_code.c_str (), expected_status_code_length);
    return 0;
}

void zmq::curve_server_t::send_zap_request (const uint8_t *key_)
{
    zap_client_t::send_zap_request ("CURVE", 5, key_,
                                    crypto_box_PUBLICKEYBYTES);
}

#endif