ch.ethz.ssh2
Class KnownHosts

java.lang.Object
  ch.ethz.ssh2.KnownHosts

public class KnownHosts
extends java.lang.Object

The 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 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).

It is a thread safe implementation, therefore, you need only to instantiate one KnownHosts for your whole application.

Version:

2.50, 03/15/10

Author:

Christian Plattner

Field Summary

static int	HOSTKEY_HAS_CHANGED
static int	HOSTKEY_IS_NEW
static int	HOSTKEY_IS_OK

Constructor Summary

KnownHosts()

KnownHosts(char[] knownHostsData)

KnownHosts(java.io.File knownHosts)

Method Summary

void	addHostkey(java.lang.String[] hostnames, java.lang.String serverHostKeyAlgorithm, byte[] serverHostKey) Adds a single public key entry to the database.
void	addHostkeys(char[] knownHostsData) Parses the given known_hosts data and adds entries to the database.
void	addHostkeys(java.io.File knownHosts) Parses the given known_hosts file and adds entries to the database.
static void	addHostkeyToFile(java.io.File knownHosts, java.lang.String[] hostnames, java.lang.String serverHostKeyAlgorithm, byte[] serverHostKey) Adds a single public key entry to the a known_hosts file.
static java.lang.String	createBubblebabbleFingerprint(java.lang.String keytype, byte[] publickey) Convert a ssh2 key-blob into a human readable bubblebabble fingerprint.
static java.lang.String	createHashedHostname(java.lang.String hostname) Generate the hashed representation of the given hostname.
static java.lang.String	createHexFingerprint(java.lang.String keytype, byte[] publickey) Convert a ssh2 key-blob into a human readable hex fingerprint.
java.lang.String[]	getPreferredServerHostkeyAlgorithmOrder(java.lang.String hostname) Try to find the preferred order of hostkey algorithms for the given hostname.
int	verifyHostkey(java.lang.String hostname, java.lang.String serverHostKeyAlgorithm, byte[] serverHostKey) Checks the internal hostkey database for the given hostkey.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

HOSTKEY_IS_OK

public static final int HOSTKEY_IS_OK

See Also:

Constant Field Values

HOSTKEY_IS_NEW

public static final int HOSTKEY_IS_NEW

See Also:

Constant Field Values

HOSTKEY_HAS_CHANGED

public static final int HOSTKEY_HAS_CHANGED

See Also:

Constant Field Values

Constructor Detail

KnownHosts

public KnownHosts()

KnownHosts

public KnownHosts(char[] knownHostsData)
           throws java.io.IOException

Throws:

java.io.IOException

KnownHosts

public KnownHosts(java.io.File knownHosts)
           throws java.io.IOException

Throws:

java.io.IOException

Method Detail

addHostkey

public void addHostkey(java.lang.String[] hostnames,
                       java.lang.String serverHostKeyAlgorithm,
                       byte[] serverHostKey)
                throws java.io.IOException

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 ServerHostKeyVerifier.

Parameters:

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.

serverHostKeyAlgorithm - as passed to the ServerHostKeyVerifier.

serverHostKey - as passed to the ServerHostKeyVerifier.

Throws:

java.io.IOException

addHostkeys

public void addHostkeys(char[] knownHostsData)
                 throws java.io.IOException

Parses the given known_hosts data and adds entries to the database.

Parameters:

knownHostsData -

Throws:

java.io.IOException

addHostkeys

public void addHostkeys(java.io.File knownHosts)
                 throws java.io.IOException

Parses the given known_hosts file and adds entries to the database.

Parameters:

knownHosts -

Throws:

java.io.IOException

createHashedHostname

public static final java.lang.String createHashedHostname(java.lang.String hostname)

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).

Parameters:

hostname -

Returns:

the hashed representation, e.g., "|1|cDhrv7zwEUV3k71CEPHnhHZezhA=|Xo+2y6rUXo2OIWRAYhBOIijbJMA="

getPreferredServerHostkeyAlgorithmOrder

public java.lang.String[] getPreferredServerHostkeyAlgorithmOrder(java.lang.String hostname)

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.

Parameters:

hostname -

Returns:

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).

verifyHostkey

public int verifyHostkey(java.lang.String hostname,
                         java.lang.String serverHostKeyAlgorithm,
                         byte[] serverHostKey)
                  throws java.io.IOException

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.

Parameters:

hostname - the server's hostname, will be matched with all hostname patterns

serverHostKeyAlgorithm - type of hostkey, either ssh-rsa or ssh-dss

serverHostKey - the key blob

Returns:

• HOSTKEY_IS_OK: the given hostkey matches an entry for the given hostname
• HOSTKEY_IS_NEW: no entries found for this hostname and this type of hostkey
• HOSTKEY_HAS_CHANGED: hostname is known, but with another key of the same type (man-in-the-middle attack?)

Throws:

java.io.IOException - if the supplied key blob cannot be parsed or does not match the given hostkey type.

addHostkeyToFile

public static final void addHostkeyToFile(java.io.File knownHosts,
                                          java.lang.String[] hostnames,
                                          java.lang.String serverHostKeyAlgorithm,
                                          byte[] serverHostKey)
                                   throws java.io.IOException

Adds a single public key entry to the a known_hosts file. This method is designed to be used in a ServerHostKeyVerifier.

Parameters:

knownHosts - the file where the publickey entry will be appended.

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.

serverHostKeyAlgorithm - as passed to the ServerHostKeyVerifier.

serverHostKey - as passed to the ServerHostKeyVerifier.

Throws:

java.io.IOException

createHexFingerprint

public static final java.lang.String createHexFingerprint(java.lang.String keytype,
                                                          byte[] publickey)

Convert a ssh2 key-blob into a human readable hex fingerprint. Generated fingerprints are identical to those generated by OpenSSH.

Example fingerprint: d0:cb:76:19:99:5a:03:fc:73:10:70:93:f2:44:63:47.

Parameters:

keytype - either "ssh-rsa" or "ssh-dss"

publickey - key blob

Returns:

Hex fingerprint

createBubblebabbleFingerprint

public static final java.lang.String createBubblebabbleFingerprint(java.lang.String keytype,
                                                                   byte[] publickey)

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.

Parameters:

keytype - either "ssh-rsa" or "ssh-dss"

publickey - key data

Returns:

Bubblebabble fingerprint