ServerKeyDatabase.java

/*
 * Copyright (C) 2019 Thomas Wolf <thomas.wolf@paranor.ch> and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */
package org.eclipse.jgit.transport.sshd;

import java.net.InetSocketAddress;
import java.security.PublicKey;
import java.util.List;

import org.eclipse.jgit.annotations.NonNull;
import org.eclipse.jgit.transport.CredentialsProvider;

/**
 * An interface for a database of known server keys, supporting finding all
 * known keys and also deciding whether a server key is to be accepted.
 * <p>
 * Connection addresses are given as strings of the format
 * {@code [hostName]:port} if using a non-standard port (i.e., not port 22),
 * otherwise just {@code hostname}.
 * </p>
 *
 * @since 5.5
 */
public interface ServerKeyDatabase {

    /**
     * Retrieves all known host keys for the given addresses.
     *
     * @param connectAddress
     *            IP address the session tried to connect to
     * @param remoteAddress
     *            IP address as reported for the remote end point
     * @param config
     *            giving access to potentially interesting configuration
     *            settings
     * @return the list of known keys for the given addresses
     */
    @NonNull
    List<PublicKey> lookup(@NonNull String connectAddress,
            @NonNull InetSocketAddress remoteAddress,
            @NonNull Configuration config);

    /**
     * Determines whether to accept a received server host key.
     *
     * @param connectAddress
     *            IP address the session tried to connect to
     * @param remoteAddress
     *            IP address as reported for the remote end point
     * @param serverKey
     *            received from the remote end
     * @param config
     *            giving access to potentially interesting configuration
     *            settings
     * @param provider
     *            for interacting with the user, if required; may be
     *            {@code null}
     * @return {@code true} if the serverKey is accepted, {@code false}
     *         otherwise
     */
    boolean accept(@NonNull String connectAddress,
            @NonNull InetSocketAddress remoteAddress,
            @NonNull PublicKey serverKey,
            @NonNull Configuration config, CredentialsProvider provider);

    /**
     * A simple provider for ssh config settings related to host key checking.
     * An instance is created by the JGit sshd framework and passed into
     * {@link ServerKeyDatabase#lookup(String, InetSocketAddress, Configuration)}
     * and
     * {@link ServerKeyDatabase#accept(String, InetSocketAddress, PublicKey, Configuration, CredentialsProvider)}.
     */
    interface Configuration {

        /**
         * Retrieves the list of file names from the "UserKnownHostsFile" ssh
         * config.
         *
         * @return the list as configured, with ~ already replaced
         */
        List<String> getUserKnownHostsFiles();

        /**
         * Retrieves the list of file names from the "GlobalKnownHostsFile" ssh
         * config.
         *
         * @return the list as configured, with ~ already replaced
         */
        List<String> getGlobalKnownHostsFiles();

        /**
         * The possible values for the "StrictHostKeyChecking" ssh config.
         */
        enum StrictHostKeyChecking {
            /**
             * "ask"; default: ask the user whether to accept (and store) a new
             * or mismatched key.
             */
            ASK,
            /**
             * "yes", "on": never accept new or mismatched keys.
             */
            REQUIRE_MATCH,
            /**
             * "no", "off": always accept new or mismatched keys.
             */
            ACCEPT_ANY,
            /**
             * "accept-new": accept new keys, but never accept modified keys.
             */
            ACCEPT_NEW
        }

        /**
         * Obtains the value of the "StrictHostKeyChecking" ssh config.
         *
         * @return the {@link StrictHostKeyChecking}
         */
        @NonNull
        StrictHostKeyChecking getStrictHostKeyChecking();

        /**
         * Obtains the value of the "HashKnownHosts" ssh config.
         *
         * @return {@code true} if new entries should be stored with hashed host
         *         information, {@code false} otherwise
         */
        boolean getHashKnownHosts();

        /**
         * Obtains the user name used in the connection attempt.
         *
         * @return the user name
         */
        @NonNull
        String getUsername();
    }
}