KnownHosts class is a handy tool to verify received server hostkeys
* based on the information in known_hosts files (the ones used by OpenSSH).
*
* It offers basically an in-memory database for known_hosts entries, as well as some
* helper functions. Entries from a
* It is a thread safe implementation, therefore, you need only to instantiate one
*
* 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.
*
* 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);
}
}
known_hosts file can be loaded at construction time.
* It is also possible to add more keys later (e.g., one can parse different
* known_hosts files).
* KnownHosts 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
{
private static final Logger LOGGER = Logger.getLogger(KnownHosts.class);
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;
Object key;
KnownHostsEntry(String[] patterns, Object key)
{
this.patterns = patterns;
this.key = key;
}
}
private LinkedList publicKeys = new LinkedList();
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 addHostkeyToFile() 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)) {
final RSAPublicKey rpk = RSASHA1Verify.decodeSSHRSAPublicKey(serverHostKey);
synchronized (publicKeys) {
publicKeys.add(new KnownHostsEntry(hostnames, rpk));
}
}
else if ("ssh-dss".equals(serverHostKeyAlgorithm)) {
final DSAPublicKey dpk = DSASHA1Verify.decodeSSHDSAPublicKey(serverHostKey);
synchronized (publicKeys) {
publicKeys.add(new KnownHostsEntry(hostnames, dpk));
}
}
else {
throw new IOWarningException("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)
{
SHA1 sha1 = new SHA1();
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)
{
SHA1 sha1 = new SHA1();
if (salt.length != sha1.getDigestLength())
throw new IllegalArgumentException("Salt has wrong length (" + salt.length + ")");
HMAC hmac = new HMAC(sha1, salt, salt.length);
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());
}
byte[] dig = new byte[hmac.getDigestLength()];
hmac.digest(dig);
return dig;
}
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;
}
SHA1 sha1 = new SHA1();
if (salt.length != sha1.getDigestLength())
return false;
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, Object remoteKey)
{
int result = HOSTKEY_IS_NEW;
synchronized (publicKeys)
{
Iterator i = publicKeys.iterator();
while (i.hasNext())
{
KnownHostsEntry ke = (KnownHostsEntry) 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 getAllKeys(String hostname)
{
Vector keys = new Vector();
synchronized (publicKeys)
{
Iterator i = publicKeys.iterator();
while (i.hasNext())
{
KnownHostsEntry ke = (KnownHostsEntry) 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 ssh-rsa or ssh-dss)
* an ordered list of hostkey algorithms is returned which can be passed
* to Connection.setServerHostKeyAlgorithms.
*
* @param hostname
* @return null 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();
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();
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;
}
else
{
final int indexColon = pattern.indexOf(':');
final int indexLastColon = pattern.indexOf(':');
if (indexColon > 0 && indexColon < pattern.length() - 2 && indexColon == indexLastColon)
{
final String bracketizedHost = '[' + hostname + ']';
if (pattern.startsWith(bracketizedHost))
{
if (negate)
return false;
isMatch = true;
}
}
}
}
}
return isMatch;
}
private void initialize(char[] knownHostsData) throws IOException {
final BufferedReader br = new BufferedReader(new CharArrayReader(knownHostsData));
for (String line = br.readLine(); line != null; line = br.readLine()) {
line = line.trim();
if (line.startsWith("#")) {
continue;
}
final String[] arr = line.split(" ");
if (arr.length < 3) {
continue;
}
final String serverHostKeyAlgorithm = arr[1];
if (!"ssh-rsa".equals(serverHostKeyAlgorithm) && !"ssh-dss".equals(serverHostKeyAlgorithm)) {
continue;
}
final String[] hostnames = arr[0].split(",");
final byte[] msg = Base64.decode(arr[2].toCharArray());
try {
addHostkey(hostnames, serverHostKeyAlgorithm, msg);
}
catch (IOWarningException ex) {
LOGGER.log(20, "Ignored invalid line '" + line + "'");
}
}
}
private void initialize(File knownHosts) throws IOException {
final char[] buffer = new char[512];
final CharArrayWriter charWriter = new CharArrayWriter();
knownHosts.createNewFile();
final Reader reader = new FileReader(knownHosts);
try {
while (true) {
final int readCharCount = reader.read(buffer);
if (readCharCount < 0) {
break;
}
charWriter.write(buffer, 0, readCharCount);
}
}
finally {
reader.close();
}
initialize(charWriter.toCharArray());
}
private final boolean matchKeys(Object key1, Object key2)
{
if ((key1 instanceof RSAPublicKey) && (key2 instanceof RSAPublicKey))
{
RSAPublicKey savedRSAKey = (RSAPublicKey) key1;
RSAPublicKey remoteRSAKey = (RSAPublicKey) key2;
if (savedRSAKey.getE().equals(remoteRSAKey.getE()) == false)
return false;
if (savedRSAKey.getN().equals(remoteRSAKey.getN()) == false)
return false;
return true;
}
if ((key1 instanceof DSAPublicKey) && (key2 instanceof DSAPublicKey))
{
DSAPublicKey savedDSAKey = (DSAPublicKey) key1;
DSAPublicKey remoteDSAKey = (DSAPublicKey) key2;
if (savedDSAKey.getG().equals(remoteDSAKey.getG()) == false)
return false;
if (savedDSAKey.getP().equals(remoteDSAKey.getP()) == false)
return false;
if (savedDSAKey.getQ().equals(remoteDSAKey.getQ()) == false)
return false;
if (savedDSAKey.getY().equals(remoteDSAKey.getY()) == false)
return false;
return true;
}
return false;
}
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 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 ssh-rsa or ssh-dss
* @param serverHostKey the key blob
* @return
*
* @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
{
Object remoteKey = null;
if ("ssh-rsa".equals(serverHostKeyAlgorithm))
{
remoteKey = RSASHA1Verify.decodeSSHRSAPublicKey(serverHostKey);
}
else if ("ssh-dss".equals(serverHostKeyAlgorithm))
{
remoteKey = DSASHA1Verify.decodeSSHDSAPublicKey(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)
{
Digest dig = null;
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
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()];
dig.digest(res);
return res;
}
/**
* 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.
* HOSTKEY_IS_OK: the given hostkey matches an entry for the given hostnameHOSTKEY_IS_NEW: no entries found for this hostname and this type of hostkeyHOSTKEY_HAS_CHANGED: hostname is known, but with another key of the same type
* (man-in-the-middle attack?)