/*
 * Copyright (c) 2006-2011 Christian Plattner. All rights reserved.
 * Please refer to the LICENSE.txt for licensing details.
 */

package ch.ethz.ssh2;

import java.io.BufferedReader;
import java.io.CharArrayReader;
import java.io.CharArrayWriter;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.DigestException;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;

import ch.ethz.ssh2.crypto.Base64;
import ch.ethz.ssh2.crypto.SecureRandomFix;
import ch.ethz.ssh2.crypto.digest.Digest;
import ch.ethz.ssh2.crypto.digest.HMAC;
import ch.ethz.ssh2.crypto.digest.MD5;
import ch.ethz.ssh2.crypto.digest.SHA1;

import java.security.KeyPair;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.interfaces.DSAPublicKey;
import java.security.interfaces.ECPublicKey;
import java.security.interfaces.RSAPublicKey;
import ch.ethz.ssh2.signature.DSASHA1Verify;
import ch.ethz.ssh2.signature.ECDSASHA2Verify;
import ch.ethz.ssh2.signature.RSASHA1Verify;
import ch.ethz.ssh2.util.StringEncoder;

/**
 * The <code>KnownHosts</code> class is a handy tool to verify received server hostkeys
 * based on the information in <code>known_hosts</code> files (the ones used by OpenSSH).
 * <p/>
 * It offers basically an in-memory database for known_hosts entries, as well as some
 * helper functions. Entries from a <code>known_hosts</code> file can be loaded at construction time.
 * It is also possible to add more keys later (e.g., one can parse different
 * <code>known_hosts<code> files).
 * <p/>
 * It is a thread safe implementation, therefore, you need only to instantiate one
 * <code>KnownHosts</code> for your whole application.
 *
 * @author Christian Plattner
 * @version $Id: KnownHosts.java 152 2014-04-28 11:02:23Z dkocher@sudo.ch $
 */

public class KnownHosts {
    public static final int HOSTKEY_IS_OK = 0;
    public static final int HOSTKEY_IS_NEW = 1;
    public static final int HOSTKEY_HAS_CHANGED = 2;

    private class KnownHostsEntry {
        String[] patterns;
        PublicKey key;

        KnownHostsEntry(String[] patterns, PublicKey key) {
            this.patterns = patterns;
            this.key = key;
        }
    }

    private final LinkedList<KnownHostsEntry> publicKeys = new LinkedList<KnownHosts.KnownHostsEntry>();

    public KnownHosts() {
    }

    public KnownHosts(char[] knownHostsData) throws IOException {
        initialize(knownHostsData);
    }

    public KnownHosts(String knownHosts) throws IOException {
        initialize(new File(knownHosts));
    }

    public KnownHosts(File knownHosts) throws IOException {
        initialize(knownHosts);
    }

    /**
     * Adds a single public key entry to the database. Note: this will NOT add the public key
     * to any physical file (e.g., "~/.ssh/known_hosts") - use <code>addHostkeyToFile()</code> for that purpose.
     * This method is designed to be used in a {@link ServerHostKeyVerifier}.
     *
     * @param hostnames              a list of hostname patterns - at least one most be specified. Check out the
     *                               OpenSSH sshd man page for a description of the pattern matching algorithm.
     * @param serverHostKeyAlgorithm as passed to the {@link ServerHostKeyVerifier}.
     * @param serverHostKey          as passed to the {@link ServerHostKeyVerifier}.
     * @throws IOException
     */
    public void addHostkey(String hostnames[], String serverHostKeyAlgorithm, byte[] serverHostKey) throws IOException {
        if (hostnames == null) {
            throw new IllegalArgumentException("hostnames may not be null");
        }

        if ("ssh-rsa".equals(serverHostKeyAlgorithm)) {
            RSAPublicKey rpk = RSASHA1Verify.decodeSSHRSAPublicKey(serverHostKey);

            synchronized (publicKeys) {
                publicKeys.add(new KnownHostsEntry(hostnames, rpk));
            }
        }
        else if ("ssh-dss".equals(serverHostKeyAlgorithm)) {
            DSAPublicKey dpk = DSASHA1Verify.decodeSSHDSAPublicKey(serverHostKey);

            synchronized (publicKeys) {
                publicKeys.add(new KnownHostsEntry(hostnames, dpk));
            }
        }
        else if (serverHostKeyAlgorithm.startsWith("ecdsa-sha2-")) {
            ECPublicKey epk = ECDSASHA2Verify.decodeSSHECDSAPublicKey(serverHostKey);

            synchronized (publicKeys) {
                publicKeys.add(new KnownHostsEntry(hostnames, epk));
            }
        }
        else {
            throw new IOException(String.format("Unknown host key type %s", serverHostKeyAlgorithm));
        }
    }

    /**
     * Parses the given known_hosts data and adds entries to the database.
     *
     * @param knownHostsData
     * @throws IOException
     */
    public void addHostkeys(char[] knownHostsData) throws IOException {
        initialize(knownHostsData);
    }

    /**
     * Parses the given known_hosts file and adds entries to the database.
     *
     * @param knownHosts
     * @throws IOException
     */
    public void addHostkeys(File knownHosts) throws IOException {
        initialize(knownHosts);
    }

    /**
     * Generate the hashed representation of the given hostname. Useful for adding entries
     * with hashed hostnames to a known_hosts file. (see -H option of OpenSSH key-gen).
     *
     * @param hostname
     * @return the hashed representation, e.g., "|1|cDhrv7zwEUV3k71CEPHnhHZezhA=|Xo+2y6rUXo2OIWRAYhBOIijbJMA="
     */
    public static String createHashedHostname(String hostname) throws IOException {
        SHA1 sha1 = new SHA1();
        byte[] salt = new byte[sha1.getDigestLength()];
        new SecureRandomFix().nextBytes(salt);
        byte[] hash;

        try {
            hash = hmacSha1Hash(salt, hostname);
        }
        catch (IOException e) {
            throw new IOException(e);
        }

        String base64_salt = new String(Base64.encode(salt));
        String base64_hash = new String(Base64.encode(hash));
        return String.format("|1|%s|%s", base64_salt, base64_hash);
    }

    private static byte[] hmacSha1Hash(byte[] salt, String hostname) throws IOException {
        SHA1 sha1 = new SHA1();

        if (salt.length != sha1.getDigestLength()) {
            throw new IllegalArgumentException("Salt has wrong length (" + salt.length + ")");
        }

        try {
            HMAC hmac = new HMAC(sha1, salt, salt.length);
            hmac.update(StringEncoder.GetBytes(hostname));
            byte[] dig = new byte[hmac.getDigestLength()];
            hmac.digest(dig);
            return dig;
        }
        catch (DigestException e) {
            throw new IOException(e);
        }
    }

    private boolean checkHashed(String entry, String hostname) {
        if (entry.startsWith("|1|") == false) {
            return false;
        }

        int delim_idx = entry.indexOf('|', 3);

        if (delim_idx == -1) {
            return false;
        }

        String salt_base64 = entry.substring(3, delim_idx);
        String hash_base64 = entry.substring(delim_idx + 1);
        byte[] salt;
        byte[] hash;

        try {
            salt = Base64.decode(salt_base64.toCharArray());
            hash = Base64.decode(hash_base64.toCharArray());
        }
        catch (IOException e) {
            return false;
        }

        SHA1 sha1 = new SHA1();

        if (salt.length != sha1.getDigestLength()) {
            return false;
        }

        byte[] dig = new byte[0];

        try {
            dig = hmacSha1Hash(salt, hostname);
        }
        catch (IOException e) {
            return false;
        }

        for (int i = 0; i < dig.length; i++) {
            if (dig[i] != hash[i]) {
                return false;
            }
        }

        return true;
    }

    private int checkKey(String remoteHostname, PublicKey remoteKey) {
        int result = HOSTKEY_IS_NEW;

        synchronized (publicKeys) {
            for (KnownHostsEntry ke : publicKeys) {
                if (hostnameMatches(ke.patterns, remoteHostname) == false) {
                    continue;
                }

                boolean res = matchKeys(ke.key, remoteKey);

                if (res == true) {
                    return HOSTKEY_IS_OK;
                }

                result = HOSTKEY_HAS_CHANGED;
            }
        }

        return result;
    }

    private List<Object> getAllKeys(String hostname) {
        List<Object> keys = new ArrayList<Object>();

        synchronized (publicKeys) {
            for (KnownHostsEntry ke : publicKeys) {
                if (hostnameMatches(ke.patterns, hostname) == false) {
                    continue;
                }

                keys.add(ke.key);
            }
        }

        return keys;
    }

    /**
     * Try to find the preferred order of hostkey algorithms for the given hostname.
     * Based on the type of hostkey that is present in the internal database
     * (i.e., either <code>ssh-rsa</code> or <code>ssh-dss</code>)
     * an ordered list of hostkey algorithms is returned which can be passed
     * to <code>Connection.setServerHostKeyAlgorithms</code>.
     *
     * @param hostname
     * @return <code>null</code> if no key for the given hostname is present or
     * there are keys of multiple types present for the given hostname. Otherwise,
     * an array with hostkey algorithms is returned (i.e., an array of length 2).
     */
    public String[] getPreferredServerHostkeyAlgorithmOrder(String hostname) {
        String[] algos = recommendHostkeyAlgorithms(hostname);

        if (algos != null) {
            return algos;
        }

        InetAddress[] ipAdresses;

        try {
            ipAdresses = InetAddress.getAllByName(hostname);
        }
        catch (UnknownHostException e) {
            return null;
        }

        for (int i = 0; i < ipAdresses.length; i++) {
            algos = recommendHostkeyAlgorithms(ipAdresses[i].getHostAddress());

            if (algos != null) {
                return algos;
            }
        }

        return null;
    }

    private boolean hostnameMatches(String[] hostpatterns, String hostname) {
        boolean isMatch = false;
        boolean negate;
        hostname = hostname.toLowerCase();

        for (int k = 0; k < hostpatterns.length; k++) {
            if (hostpatterns[k] == null) {
                continue;
            }

            String pattern;

            /* In contrast to OpenSSH we also allow negated hash entries (as well as hashed
                            * entries in lines with multiple entries).
                            */

            if ((hostpatterns[k].length() > 0) && (hostpatterns[k].charAt(0) == '!')) {
                pattern = hostpatterns[k].substring(1);
                negate = true;
            }
            else {
                pattern = hostpatterns[k];
                negate = false;
            }

            /* Optimize, no need to check this entry */

            if ((isMatch) && (negate == false)) {
                continue;
            }

            /* Now compare */

            if (pattern.charAt(0) == '|') {
                if (checkHashed(pattern, hostname)) {
                    if (negate) {
                        return false;
                    }

                    isMatch = true;
                }
            }
            else {
                pattern = pattern.toLowerCase();

                if ((pattern.indexOf('?') != -1) || (pattern.indexOf('*') != -1)) {
                    if (pseudoRegex(pattern.toCharArray(), 0, hostname.toCharArray(), 0)) {
                        if (negate) {
                            return false;
                        }

                        isMatch = true;
                    }
                }
                else if (pattern.compareTo(hostname) == 0) {
                    if (negate) {
                        return false;
                    }

                    isMatch = true;
                }
            }
        }

        return isMatch;
    }

    private void initialize(char[] knownHostsData) throws IOException {
        BufferedReader br = new BufferedReader(new CharArrayReader(knownHostsData));

        while (true) {
            String line = br.readLine();

            if (line == null) {
                break;
            }

            line = line.trim();

            if (line.startsWith("#")) {
                continue;
            }

            String[] arr = line.split(" ");

            if (arr.length >= 3) {
                if ((arr[1].compareTo("ssh-rsa") == 0) ||
                        (arr[1].compareTo("ssh-dss") == 0) ||
                        (arr[1].startsWith("ecdsa-sha2-"))) {
                    String[] hostnames = arr[0].split(",");
                    byte[] msg = Base64.decode(arr[2].toCharArray());

                    try {
                        addHostkey(hostnames, arr[1], msg);
                    }
                    catch (IOException e) {
                        continue;
                    }
                }
            }
        }
    }

    private void initialize(File knownHosts) throws IOException {
        char[] buff = new char[512];
        CharArrayWriter cw = new CharArrayWriter();
        knownHosts.createNewFile();
        FileReader fr = new FileReader(knownHosts);

        while (true) {
            int len = fr.read(buff);

            if (len < 0) {
                break;
            }

            cw.write(buff, 0, len);
        }

        fr.close();
        initialize(cw.toCharArray());
    }

    private final boolean matchKeys(PublicKey key1, PublicKey key2) {
        return key1.equals(key2);
    }

    private boolean pseudoRegex(char[] pattern, int i, char[] match, int j) {
        /* This matching logic is equivalent to the one present in OpenSSH 4.1 */
        while (true) {
            /* Are we at the end of the pattern? */
            if (pattern.length == i) {
                return (match.length == j);
            }

            if (pattern[i] == '*') {
                i++;

                if (pattern.length == i) {
                    return true;
                }

                if ((pattern[i] != '*') && (pattern[i] != '?')) {
                    while (true) {
                        if ((pattern[i] == match[j]) && pseudoRegex(pattern, i + 1, match, j + 1)) {
                            return true;
                        }

                        j++;

                        if (match.length == j) {
                            return false;
                        }
                    }
                }

                while (true) {
                    if (pseudoRegex(pattern, i, match, j)) {
                        return true;
                    }

                    j++;

                    if (match.length == j) {
                        return false;
                    }
                }
            }

            if (match.length == j) {
                return false;
            }

            if ((pattern[i] != '?') && (pattern[i] != match[j])) {
                return false;
            }

            i++;
            j++;
        }
    }

    private String[] recommendHostkeyAlgorithms(String hostname) {
        String preferredAlgo = null;
        List<Object> keys = getAllKeys(hostname);

        for (Object key : keys) {
            String thisAlgo;

            if (key instanceof RSAPublicKey) {
                thisAlgo = "ssh-rsa";
            }
            else if (key instanceof DSAPublicKey) {
                thisAlgo = "ssh-dss";
            }
            else if (key instanceof ECPublicKey) {
                ECPublicKey ecPub = (ECPublicKey) key;
                String keyType = ECDSASHA2Verify.getCurveName(ecPub.getParams().getCurve().getField().getFieldSize());
                thisAlgo = ECDSASHA2Verify.ECDSA_SHA2_PREFIX + keyType;
            }
            else {
                continue;
            }

            if (preferredAlgo != null) {
                /* If we find different key types, then return null */
                if (preferredAlgo.compareTo(thisAlgo) != 0) {
                    return null;
                }
            }
            else {
                preferredAlgo = thisAlgo;
            }
        }

        /* If we did not find anything that we know of, return null */

        if (preferredAlgo == null) {
            return null;
        }

        /* Now put the preferred algo to the start of the array.
                   * You may ask yourself why we do it that way - basically, we could just
                   * return only the preferred algorithm: since we have a saved key of that
                   * type (sent earlier from the remote host), then that should work out.
                   * However, imagine that the server is (for whatever reasons) not offering
                   * that type of hostkey anymore (e.g., "ssh-rsa" was disabled and
                   * now "ssh-dss" is being used). If we then do not let the server send us
                   * a fresh key of the new type, then we shoot ourself into the foot:
                   * the connection cannot be established and hence the user cannot decide
                   * if he/she wants to accept the new key.
                   */

        if (preferredAlgo.equals("ssh-rsa")) {
            return new String[] {"ssh-rsa", "ssh-dss", "ecdsa-sha2-nistp256"};
        }

        return new String[] {"ssh-dss", "ssh-rsa", "ecdsa-sha2-nistp256"};
    }

    /**
     * Checks the internal hostkey database for the given hostkey.
     * If no matching key can be found, then the hostname is resolved to an IP address
     * and the search is repeated using that IP address.
     *
     * @param hostname               the server's hostname, will be matched with all hostname patterns
     * @param serverHostKeyAlgorithm type of hostkey, either <code>ssh-rsa</code> or <code>ssh-dss</code>
     * @param serverHostKey          the key blob
     * @return <ul>
     * <li><code>HOSTKEY_IS_OK</code>: the given hostkey matches an entry for the given hostname</li>
     * <li><code>HOSTKEY_IS_NEW</code>: no entries found for this hostname and this type of hostkey</li>
     * <li><code>HOSTKEY_HAS_CHANGED</code>: hostname is known, but with another key of the same type
     * (man-in-the-middle attack?)</li>
     * </ul>
     * @throws IOException if the supplied key blob cannot be parsed or does not match the given hostkey type.
     */
    public int verifyHostkey(String hostname, String serverHostKeyAlgorithm, byte[] serverHostKey) throws IOException {
        PublicKey remoteKey;

        if ("ssh-rsa".equals(serverHostKeyAlgorithm)) {
            remoteKey = RSASHA1Verify.decodeSSHRSAPublicKey(serverHostKey);
        }
        else if ("ssh-dss".equals(serverHostKeyAlgorithm)) {
            remoteKey = DSASHA1Verify.decodeSSHDSAPublicKey(serverHostKey);
        }
        else if (serverHostKeyAlgorithm.startsWith("ecdsa-sha2-")) {
            remoteKey = ECDSASHA2Verify.decodeSSHECDSAPublicKey(serverHostKey);
        }
        else {
            throw new IllegalArgumentException("Unknown hostkey type " + serverHostKeyAlgorithm);
        }

        int result = checkKey(hostname, remoteKey);

        if (result == HOSTKEY_IS_OK) {
            return result;
        }

        InetAddress[] ipAdresses;

        try {
            ipAdresses = InetAddress.getAllByName(hostname);
        }
        catch (UnknownHostException e) {
            return result;
        }

        for (int i = 0; i < ipAdresses.length; i++) {
            int newresult = checkKey(ipAdresses[i].getHostAddress(), remoteKey);

            if (newresult == HOSTKEY_IS_OK) {
                return newresult;
            }

            if (newresult == HOSTKEY_HAS_CHANGED) {
                result = HOSTKEY_HAS_CHANGED;
            }
        }

        return result;
    }

    /**
     * Adds a single public key entry to the a known_hosts file.
     * This method is designed to be used in a {@link ServerHostKeyVerifier}.
     *
     * @param knownHosts             the file where the publickey entry will be appended.
     * @param hostnames              a list of hostname patterns - at least one most be specified. Check out the
     *                               OpenSSH sshd man page for a description of the pattern matching algorithm.
     * @param serverHostKeyAlgorithm as passed to the {@link ServerHostKeyVerifier}.
     * @param serverHostKey          as passed to the {@link ServerHostKeyVerifier}.
     * @throws IOException
     */
    public static void addHostkeyToFile(File knownHosts, String[] hostnames, String serverHostKeyAlgorithm,
                                        byte[] serverHostKey) throws IOException {
        if ((hostnames == null) || (hostnames.length == 0)) {
            throw new IllegalArgumentException("Need at least one hostname specification");
        }

        if ((serverHostKeyAlgorithm == null) || (serverHostKey == null)) {
            throw new IllegalArgumentException();
        }

        CharArrayWriter writer = new CharArrayWriter();

        for (int i = 0; i < hostnames.length; i++) {
            if (i != 0) {
                writer.write(',');
            }

            writer.write(hostnames[i]);
        }

        writer.write(' ');
        writer.write(serverHostKeyAlgorithm);
        writer.write(' ');
        writer.write(Base64.encode(serverHostKey));
        writer.write("\n");
        char[] entry = writer.toCharArray();
        RandomAccessFile raf = new RandomAccessFile(knownHosts, "rw");
        long len = raf.length();

        if (len > 0) {
            raf.seek(len - 1);
            int last = raf.read();

            if (last != '\n') {
                raf.write('\n');
            }
        }

        raf.write(StringEncoder.GetBytes(new String(entry)));
        raf.close();
    }

    /**
     * Generates a "raw" fingerprint of a hostkey.
     *
     * @param type    either "md5" or "sha1"
     * @param keyType either "ssh-rsa" or "ssh-dss" or "ecdsa-sha2..."
     * @param hostkey the hostkey
     * @return the raw fingerprint
     */
    static private byte[] rawFingerPrint(String type, String keyType, byte[] hostkey) throws IOException {
        Digest dig;

        if ("md5".equals(type)) {
            dig = new MD5();
        }
        else if ("sha1".equals(type)) {
            dig = new SHA1();
        }
        else {
            throw new IllegalArgumentException("Unknown hash type " + type);
        }

        if ("ssh-rsa".equals(keyType)) {
        }
        else if ("ssh-dss".equals(keyType)) {
        }
        else if (keyType.startsWith("ecdsa-sha2-")) {
        }
        else {
            throw new IllegalArgumentException("Unknown key type " + keyType);
        }

        if (hostkey == null) {
            throw new IllegalArgumentException("hostkey is null");
        }

        dig.update(hostkey);
        byte[] res = new byte[dig.getDigestLength()];

        try {
            dig.digest(res);
        }
        catch (DigestException e) {
            throw new IOException(e);
        }

        return res;
    }

    /**
     * Convert a raw fingerprint to hex representation (XX:YY:ZZ...).
     *
     * @param fingerprint raw fingerprint
     * @return the hex representation
     */
    static private String rawToHexFingerprint(byte[] fingerprint) {
        final char[] alpha = "0123456789abcdef".toCharArray();
        StringBuilder sb = new StringBuilder();

        for (int i = 0; i < fingerprint.length; i++) {
            if (i != 0) {
                sb.append(':');
            }

            int b = fingerprint[i] & 0xff;
            sb.append(alpha[b >> 4]);
            sb.append(alpha[b & 15]);
        }

        return sb.toString();
    }

    /**
     * Convert a raw fingerprint to bubblebabble representation.
     *
     * @param raw raw fingerprint
     * @return the bubblebabble representation
     */
    static private String rawToBubblebabbleFingerprint(byte[] raw) {
        final char[] v = "aeiouy".toCharArray();
        final char[] c = "bcdfghklmnprstvzx".toCharArray();
        StringBuilder sb = new StringBuilder();
        int seed = 1;
        int rounds = (raw.length / 2) + 1;
        sb.append('x');

        for (int i = 0; i < rounds; i++) {
            if (((i + 1) < rounds) || ((raw.length) % 2 != 0)) {
                sb.append(v[(((raw[2 * i] >> 6) & 3) + seed) % 6]);
                sb.append(c[(raw[2 * i] >> 2) & 15]);
                sb.append(v[((raw[2 * i] & 3) + (seed / 6)) % 6]);

                if ((i + 1) < rounds) {
                    sb.append(c[(((raw[(2 * i) + 1])) >> 4) & 15]);
                    sb.append('-');
                    sb.append(c[(((raw[(2 * i) + 1]))) & 15]);
                    // As long as seed >= 0, seed will be >= 0 afterwards
                    seed = ((seed * 5) + (((raw[2 * i] & 0xff) * 7) + (raw[(2 * i) + 1] & 0xff))) % 36;
                }
            }
            else {
                sb.append(v[seed % 6]); // seed >= 0, therefore index positive
                sb.append('x');
                sb.append(v[seed / 6]);
            }
        }

        sb.append('x');
        return sb.toString();
    }

    /**
     * Convert a ssh2 key-blob into a human readable hex fingerprint.
     * Generated fingerprints are identical to those generated by OpenSSH.
     * <p/>
     * Example fingerprint: d0:cb:76:19:99:5a:03:fc:73:10:70:93:f2:44:63:47.
     *
     * @param keytype   either "ssh-rsa" or "ssh-dss" or "ecdsa-sha2..."
     * @param publickey key blob
     * @return Hex fingerprint
     */
    public static String createHexFingerprint(String keytype, byte[] publickey) throws IOException {
        byte[] raw = rawFingerPrint("md5", keytype, publickey);
        return rawToHexFingerprint(raw);
    }

    /**
     * Convert a ssh2 key-blob into a human readable bubblebabble fingerprint.
     * The used bubblebabble algorithm (taken from OpenSSH) generates fingerprints
     * that are easier to remember for humans.
     * <p/>
     * Example fingerprint: xofoc-bubuz-cazin-zufyl-pivuk-biduk-tacib-pybur-gonar-hotat-lyxux.
     *
     * @param keytype   either "ssh-rsa" or "ssh-dss"
     * @param publickey key data
     * @return Bubblebabble fingerprint
     */
    public static String createBubblebabbleFingerprint(String keytype, byte[] publickey) throws IOException {
        byte[] raw = rawFingerPrint("sha1", keytype, publickey);
        return rawToBubblebabbleFingerprint(raw);
    }
}