PskKeyManager

public abstract class PskKeyManager
extends Object implements KeyManager

Provider of key material for pre-shared key (PSK) key exchange used in TLS-PSK cipher suites.

Overview of TLS-PSK

TLS-PSK is a set of TLS/SSL cipher suites which rely on a symmetric pre-shared key (PSK) to secure the TLS/SSL connection and mutually authenticate its peers. These cipher suites may be a more natural fit compared to conventional public key based cipher suites in some scenarios where communication between peers is bootstrapped via a separate step (for example, a pairing step) and requires both peers to authenticate each other. In such scenarios a symmetric key (PSK) can be exchanged during the bootstrapping step, removing the need to generate and exchange public key pairs and X.509 certificates.

When a TLS-PSK cipher suite is used, both peers have to use the same key for the TLS/SSL handshake to succeed. Thus, both peers are implicitly authenticated by a successful handshake. This removes the need to use a TrustManager in conjunction with this KeyManager.

Supporting multiple keys

A peer may have multiple keys to choose from. To help choose the right key, during the handshake the server can provide a PSK identity hint to the client, and the client can provide a PSK identity to the server. The contents of these two pieces of information are specific to application-level protocols.

NOTE: Both the PSK identity hint and the PSK identity are transmitted in cleartext. Moreover, these data are received and processed prior to peer having been authenticated. Thus, they must not contain or leak key material or other sensitive information, and should be treated (e.g., parsed) with caution, as untrusted data.

The high-level flow leading to peers choosing a key during TLS/SSL handshake is as follows:

1. Server receives a handshake request from client.
2. Server replies, optionally providing a PSK identity hint to client.
3. Client chooses the key.
4. Client provides a PSK identity of the chosen key to server.
5. Server chooses the key.

In the flow above, either peer can signal that they do not have a suitable key, in which case the the handshake will be aborted immediately. This may enable a network attacker who does not know the key to learn which PSK identity hints or PSK identities are supported. If this is a concern then a randomly generated key should be used in the scenario where no key is available. This will lead to the handshake aborting later, due to key mismatch -- same as in the scenario where a key is available -- making it appear to the attacker that all PSK identity hints and PSK identities are supported.

Maximum sizes

The maximum supported sizes are as follows:

• 256 bytes for keys (see MAX_KEY_LENGTH_BYTES),
• 128 bytes for PSK identity and PSK identity hint (in modified UTF-8 representation) (see MAX_IDENTITY_LENGTH_BYTES and MAX_IDENTITY_HINT_LENGTH_BYTES).

Subclassing

Known issues

Example

 PskKeyManager pskKeyManager = ...;

 SSLContext sslContext = SSLContext.getInstance("TLS");
 sslContext.init(
         new KeyManager[] { pskKeyManager },
         new TrustManager[0], // No TrustManagers needed for TLS-PSK
         null // Use the default source of entropy
         );

 SSLSocket sslSocket = (SSLSocket) sslContext.getSocketFactory().createSocket(...);
 

Summary

Inherited methods

From class java.lang.Object Object clone() Creates and returns a copy of this object. boolean equals(Object obj) Indicates whether some other object is "equal to" this one. void finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. final Class<?> getClass() Returns the runtime class of this Object. int hashCode() Returns a hash code value for the object. final void notify() Wakes up a single thread that is waiting on this object's monitor. final void notifyAll() Wakes up all threads that are waiting on this object's monitor. String toString() Returns a string representation of the object. final void wait(long millis, int nanos) Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed. final void wait(long millis) Causes the current thread to wait until either another thread invokes the notify() method or the notifyAll() method for this object, or a specified amount of time has elapsed. final void wait() Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object.

Constants

int MAX_IDENTITY_HINT_LENGTH_BYTES

int MAX_IDENTITY_LENGTH_BYTES

int MAX_KEY_LENGTH_BYTES

Public constructors

PskKeyManager ()

Public methods

String chooseClientKeyIdentity (String identityHint, 
                SSLEngine engine)

String chooseClientKeyIdentity (String identityHint, 
                Socket socket)

String chooseServerKeyIdentityHint (SSLEngine engine)

String chooseServerKeyIdentityHint (Socket socket)

SecretKey getKey (String identityHint, 
                String identity, 
                Socket socket)

SecretKey getKey (String identityHint, 
                String identity, 
                SSLEngine engine)