com.trilead.ssh2

Class 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.

Field Summary

static int
HOSTKEY_HAS_CHANGED
static int
HOSTKEY_IS_NEW
static int
HOSTKEY_IS_OK

Constructor Summary

KnownHosts()
KnownHosts(File knownHosts)
KnownHosts(char[] knownHostsData)

Method Summary

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

Field Details

HOSTKEY_HAS_CHANGED

public static final int HOSTKEY_HAS_CHANGED
Field Value:
2

HOSTKEY_IS_NEW

public static final int HOSTKEY_IS_NEW
Field Value:
1

HOSTKEY_IS_OK

public static final int HOSTKEY_IS_OK
Field Value:
0

Constructor Details

KnownHosts

public KnownHosts()

KnownHosts

public KnownHosts(File knownHosts)
            throws IOException

KnownHosts

public KnownHosts(char[] knownHostsData)
            throws IOException

Method Details

addHostkey

public void addHostkey(hostnames[] ,
                       String serverHostKeyAlgorithm,
                       byte[] serverHostKey)
            throws IOException
Parameters:
serverHostKeyAlgorithm - as passed to the ServerHostKeyVerifier.
serverHostKey - as passed to the ServerHostKeyVerifier.

addHostkeyToFile

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

addHostkeys

public void addHostkeys(File knownHosts)
            throws IOException
Parses the given known_hosts file and adds entries to the database.
Parameters:
knownHosts -

addHostkeys

public void addHostkeys(char[] knownHostsData)
            throws IOException
Parses the given known_hosts data and adds entries to the database.
Parameters:
knownHostsData -

createBubblebabbleFingerprint

public static final String createBubblebabbleFingerprint(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

createHashedHostname

public static final String createHashedHostname(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="

createHexFingerprint

public static final String createHexFingerprint(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

getPreferredServerHostkeyAlgorithmOrder

public String[] getPreferredServerHostkeyAlgorithmOrder(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(String hostname,
                         String serverHostKeyAlgorithm,
                         byte[] serverHostKey)
            throws 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?)