Class PreSharedKey

  extended by javax.crypto.spec.SecretKeySpec
      extended by iaik.security.ssl.PreSharedKey
All Implemented Interfaces:
java.io.Serializable, java.security.Key, java.security.spec.KeySpec, javax.crypto.SecretKey

public class PreSharedKey
extends javax.crypto.spec.SecretKeySpec

Pre-shared key to be used by PSK cipher suites according to RFC 4279.

A pre-shared key is a symmetric key shared between client and server in advance. It is used for authentication when a PSK cipher suite is selected.
Although this class is implemented as JCE SecretKey a PreSharedKey object typically will not be used with JCE Cipher or Mac engines. Pre shared keys are required by PSK cipher suites to build the premaster secret. An application that wants to run a PSK cipher suite has to tell iSaSiLk which pre-shared key have to be used for peer authentication. Using SecretKey instance for pre-shared keys allows an application to use Java KeyStores for securely storing a pre-shared key. However, it may be appropriate to limit the exposure of pre-shared keys over times (see security considerations of the TLS-PSK specification).

When client and server agree on a psk cipher suite, the client has to tell the server which pre-shared key (psk) shall be used by sending the psk identity within the ClientKeyExchange message. If the server has a pre-shared key for the received identity the handshake can continue, otherwise the handshake will fail. Before receiving the psk identity in the ClientKeyExchange message, the server may use the ServerKeyExchange message to send a psk identity hint to help the client to select a proper pre-shared key. However, the TLS-PSK specification recommends that an identity hint should not be sent by the server and that it must be ignored by the client (except for a special profile makes some other recommendation).

iSaSiLk wraps pre-shared keys into PSKCredentials. Each PSKCredential binds a pre-shared key to a psk identity. Optionally a PSKCredential may also contain a psk identity hint for the pre-shared key and identification information of the peer to which to authenticate with the pre-shared key of the credential.
PSKCredentials are maintained by the PSKManager who is responsible for providing the right pre-shared key when going into a TLS connection with some particular peer. On the server side, the PSKManager searches for the psk by means of the psk identity received from the client. On the client side, the PSKManager needs to know the remote peer id to search for the right pre-shared key. You may write and plug-in your own PSKManager; however, in general you may not take care about PSKManager details at all and only use the SSLContext addPSKCredential, setPSKCredential methods to add/set PSKCredentials for being used for psk cipher suite based TLS authentication. To, for instance, tell iSaSiLk to use a pre-shared key with identity "pskclient.iaik.tugraz.at" for communicating with a server named "pskserver.iaik.tugraz.at" you may create and add a PSKCredential in the following way:

 // psk identity
 String identity = "pskclient.iaik.tugraz.at";
 // server name (remote peer id)
 String serverName = "pskserver.iaik.tugraz.at";
 // the pre-shared key
 PreSharedKey psk = ...;
 // create PSKCredential
 PSKCredential pskCredential = new PSKCredential(identity, psk);
 // set remote peer id
 // create client context
 SSLClientContext context = new SSLClientContext();
 // add PSKCredential
 // enable PSK cipher suites
 CipherSuiteList suites = new CipherSuiteList();
When calling method addPSKCredential iSaSiLk forwards the given PSKCredential to the internal PSKManager. When then connecting to the server with the remote peer id specified in the credential just added, the PSKManager returns this credential and iSaSiLk can use it for authenticating the TLS session with this server.

In the sample above we have enabled all psk based cipher suites by calling suites.add(CipherSuite.CS_ALL_PSK);. However, you also can enable one specific cipher suite only (e.g. CipherSuite.TLS_PSK_WITH_3DES_EDE_CBC_SHA) or any of the three defined sets of psk based cipher suites:

  1. Cipher suites that use symmetric key operations for authentication only:
  2. Cipher suites that use a Diffie-Hellman key exchange authenticated with a pre-shared key:
  3. Cipher suites Cipher suites that use a RSA public key authentication of the server and pre-shared key authentication of the client:

See Also:
PSKCredential, PSKManager, SSLContext.addPSKCredential(PSKCredential), SSLContext.setPSKCredential(PSKCredential), SSLContext.getPSKCredential(byte[], SSLTransport), Serialized Form

Constructor Summary
PreSharedKey(byte[] psk)
          Creates a PreSharedKey object from given key material.
Method Summary
 void destroyCriticalData()
          Destroys the critical data of this object.
 boolean equals(java.lang.Object obj)
          Compares two pre shared keys.
 java.lang.String getAlgorithm()
          Returns the name ("PSK") of the key algorithm for this key.
 byte[] getEncoded()
          Returns a copy of the key material as byte array.
 java.lang.String getFormat()
          Returns the format name ("RAW").
 int hashCode()
          Returns a hash code value for this object.
 java.lang.String toString()
          Returns a string representation of this PreSharedKey.
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail


public PreSharedKey(byte[] psk)
Creates a PreSharedKey object from given key material.

psk - the key material as byte array
Method Detail


public byte[] getEncoded()
Returns a copy of the key material as byte array.

Specified by:
getEncoded in interface java.security.Key
getEncoded in class javax.crypto.spec.SecretKeySpec
a copy of the key material as byte array


public java.lang.String getAlgorithm()
Returns the name ("PSK") of the key algorithm for this key.

Specified by:
getAlgorithm in interface java.security.Key
getAlgorithm in class javax.crypto.spec.SecretKeySpec


public java.lang.String getFormat()
Returns the format name ("RAW").

Specified by:
getFormat in interface java.security.Key
getFormat in class javax.crypto.spec.SecretKeySpec


public void destroyCriticalData()
Destroys the critical data of this object.


public boolean equals(java.lang.Object obj)
Compares two pre shared keys.

equals in class javax.crypto.spec.SecretKeySpec
obj - an object to be compared with this key
true if the object to be compared has the same value; false otherwise


public int hashCode()
Returns a hash code value for this object.

hashCode in class javax.crypto.spec.SecretKeySpec
a hash code value for this object


public java.lang.String toString()
Returns a string representation of this PreSharedKey.

toString in class java.lang.Object
a string giving some information about this secret key

This Javadoc may contain text parts from text parts from IETF Internet Standard specifications (see copyright note).

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