aboutsummaryrefslogtreecommitdiffstats
path: root/app/src/main/java/com/trilead/ssh2/KnownHosts.java
blob: ec022ff375235976279608dc89358a8f1b29525c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
package com.trilead.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.io.UnsupportedEncodingException;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.InvalidKeyException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.interfaces.DSAPublicKey;
import java.security.interfaces.ECPublicKey;
import java.security.interfaces.RSAPublicKey;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Locale;
import java.util.Vector;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

import com.trilead.ssh2.crypto.Base64;
import com.trilead.ssh2.signature.DSASHA1Verify;
import com.trilead.ssh2.signature.ECDSASHA2Verify;
import com.trilead.ssh2.signature.RSASHA1Verify;


/**
 * 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, plattner@trilead.com
 * @version $Id: KnownHosts.java,v 1.2 2008/04/01 12:38:09 cplattne Exp $
 */

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 LinkedList<KnownHostsEntry> publicKeys = new LinkedList<KnownHostsEntry>();

	public KnownHosts()
	{
	}

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

	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(ECDSASHA2Verify.ECDSA_SHA2_PREFIX))
		{
			ECPublicKey epk = ECDSASHA2Verify.decodeSSHECDSAPublicKey(serverHostKey);

			synchronized (publicKeys) {
				publicKeys.add(new KnownHostsEntry(hostnames, epk));
			}
		}
		else
			throw new IOException("Unknwon host key type (" + 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 final String createHashedHostname(String hostname)
	{
		MessageDigest sha1;
		try {
			sha1 = MessageDigest.getInstance("SHA1");
		} catch (NoSuchAlgorithmException e) {
			throw new RuntimeException("VM doesn't support SHA1", e);
		}

		byte[] salt = new byte[sha1.getDigestLength()];

		new SecureRandom().nextBytes(salt);

		byte[] hash = hmacSha1Hash(salt, hostname);

		String base64_salt = new String(Base64.encode(salt));
		String base64_hash = new String(Base64.encode(hash));

		return new String("|1|" + base64_salt + "|" + base64_hash);
	}

	private static final byte[] hmacSha1Hash(byte[] salt, String hostname)
	{
		Mac hmac;
		try {
			hmac = Mac.getInstance("HmacSHA1");
			if (salt.length != hmac.getMacLength())
				throw new IllegalArgumentException("Salt has wrong length (" + salt.length + ")");
			hmac.init(new SecretKeySpec(salt, "HmacSHA1"));
		} catch (NoSuchAlgorithmException e) {
			throw new RuntimeException("Unable to HMAC-SHA1", e);
		} catch (InvalidKeyException e) {
			throw new RuntimeException("Unable to create SecretKey", e);
		}

		try
		{
			hmac.update(hostname.getBytes("ISO-8859-1"));
		}catch(UnsupportedEncodingException ignore)
		{
			/* Actually, ISO-8859-1 is supported by all correct
			 * Java implementations. But... you never know. */
			hmac.update(hostname.getBytes());
		}

		return hmac.doFinal();
	}

	private final 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 = null;
		byte[] hash = null;

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

		try {
			MessageDigest sha1 = MessageDigest.getInstance("SHA1");
			if (salt.length != sha1.getDigestLength())
				return false;
		} catch (NoSuchAlgorithmException e) {
			throw new RuntimeException("VM does not support SHA1", e);
		}

		byte[] dig = hmacSha1Hash(salt, hostname);

		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)
		{
			Iterator<KnownHostsEntry> i = publicKeys.iterator();

			while (i.hasNext())
			{
				KnownHostsEntry ke = i.next();

				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 Vector<PublicKey> getAllKeys(String hostname)
	{
		Vector<PublicKey> keys = new Vector<PublicKey>();

		synchronized (publicKeys)
		{
			Iterator<KnownHostsEntry> i = publicKeys.iterator();

			while (i.hasNext())
			{
				KnownHostsEntry ke = i.next();

				if (hostnameMatches(ke.patterns, hostname) == false)
					continue;

				keys.addElement(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 = null;

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

		hostname = hostname.toLowerCase(Locale.US);

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

			String pattern = null;

			/* 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(Locale.US);

				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))
				{
					String[] hostnames = arr[0].split(",");

					byte[] msg = Base64.decode(arr[2].toCharArray());

					addHostkey(hostnames, arr[1], msg);
				}
			}
		}
	}

	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 final 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;

		Vector<PublicKey> keys = getAllKeys(hostname);

		for (int i = 0; i < keys.size(); i++)
		{
			String thisAlgo = null;

			if (keys.elementAt(i) instanceof RSAPublicKey)
				thisAlgo = "ssh-rsa";
			else if (keys.elementAt(i) instanceof DSAPublicKey)
				thisAlgo = "ssh-dss";
			else
				continue;

			if (preferredAlgo != null)
			{
				/* If we find different key types, then return null */

				if (preferredAlgo.compareTo(thisAlgo) != 0)
					return null;

				/* OK, we found the same algo again, optimize */

				continue;
			}
		}

		/* 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" };

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

	/**
	 * 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 = null;

		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 = null;

		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 final 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(new String(entry).getBytes("ISO-8859-1"));
		raf.close();
	}

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

		try {
			if ("md5".equals(type))
			{
				dig = MessageDigest.getInstance("MD5");
			}
			else if ("sha1".equals(type))
			{
				dig = MessageDigest.getInstance("SHA1");
			}
			else
			{
				throw new IllegalArgumentException("Unknown hash type " + type);
			}
		} catch (NoSuchAlgorithmException e) {
			throw new IllegalArgumentException("Unknown hash type " + type);
		}

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

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

		dig.update(hostkey);
		return dig.digest();
	}

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

		StringBuffer sb = new StringBuffer();

		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 final private String rawToBubblebabbleFingerprint(byte[] raw)
	{
		final char[] v = "aeiouy".toCharArray();
		final char[] c = "bcdfghklmnprstvzx".toCharArray();

		StringBuffer sb = new StringBuffer();

		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"
	 * @param publickey key blob
	 * @return Hex fingerprint
	 */
	public final static String createHexFingerprint(String keytype, byte[] publickey)
	{
		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 final static String createBubblebabbleFingerprint(String keytype, byte[] publickey)
	{
		byte[] raw = rawFingerPrint("sha1", keytype, publickey);
		return rawToBubblebabbleFingerprint(raw);
	}
}