This interface encapsulates the GSS-API security context and provides the security services that are available over the context. Security contexts are established between peers using locally acquired credentials. Multiple contexts may exist simultaneously between a pair of peers, using the same or different set of credentials. GSS-API functions in a manner independent of the underlying transport protocol and depends on its calling application to transport the tokens that are generated by the security context between the peers.

If the caller instantiates the context using the default GSSManager instance, then the Kerberos v5 GSS-API mechanism is guaranteed to be available for context establishment. This mechanism is identified by the Oid "1.2.840.113554.1.2.2" and is defined in RFC 1964.

Before the context establishment phase is initiated, the context initiator may request specific characteristics desired of the established context. Not all underlying mechanisms support all characteristics that a caller might desire. After the context is established, the caller can check the actual characteristics and services offered by that context by means of various query methods. When using the Kerberos v5 GSS-API mechanism offered by the default GSSManager instance, all optional services will be available locally. They are mutual authentication, credential delegation, confidentiality and integrity protection, and per-message replay detection and sequencing. Note that in the GSS-API, message integrity is a prerequisite for message confidentiality.

The context establishment occurs in a loop where the initiator calls initSecContext and the acceptor calls acceptSecContext until the context is established. While in this loop the initSecContext and acceptSecContext methods produce tokens that the application sends over to the peer. The peer passes any such token as input to its acceptSecContext or initSecContext as the case may be.

During the context establishment phase, the isProtReady method may be called to determine if the context can be used for the per-message operations of wrap and getMIC. This allows applications to use per-message operations on contexts which aren't yet fully established.

After the context has been established or the isProtReady method returns true, the query routines can be invoked to determine the actual characteristics and services of the established context. The application can also start using the per-message methods of wrap and getMIC to obtain cryptographic operations on application supplied data.

When the context is no longer needed, the application should call dispose to release any system resources the context may be using.

A security context typically maintains sequencing and replay detection information about the tokens it processes. Therefore, the sequence in which any tokens are presented to this context for processing can be important. Also note that none of the methods in this interface are synchronized. Therefore, it is not advisable to share a GSSContext among several threads unless some application level synchronization is in place.

The stream-based methods of GSSContext have been deprecated in Java SE 11. These methods have also been removed from RFC 8353: Generic Security Service API Version 2: Java Bindings Update for the following reasons (see section 11): "The overloaded methods of GSSContext that use input and output streams as the means to convey authentication and per-message GSS-API tokens as described in Section 5.15 of RFC 5653 are removed in this update as the wire protocol should be defined by an application and not a library. It's also impossible to implement these methods correctly when the token has no self-framing (where the end cannot be determined), or the library has no knowledge of the token format (for example, as a bridge talking to another GSS library)". These methods include initSecContext(InputStream, OutputStream), acceptSecContext(InputStream, OutputStream), wrap(InputStream, OutputStream, MessageProp), unwrap(InputStream, OutputStream, MessageProp), getMIC(InputStream, OutputStream, MessageProp), and verifyMIC(InputStream, InputStream, MessageProp).

The example code presented below demonstrates the usage of the GSSContext interface for the initiating peer. Different operations on the GSSContext object are presented, including: object instantiation, setting of desired flags, context establishment, query of actual context flags, per-message operations on application data, and finally context deletion.

   // Create a context using default credentials
   // and the implementation specific default mechanism
   GSSManager manager = ...
   GSSName targetName = ...
   GSSContext context = manager.createContext(targetName, null, null,
                                          GSSContext.INDEFINITE_LIFETIME);

   // set desired context options prior to context establishment
   context.requestConf(true);
   context.requestMutualAuth(true);
   context.requestReplayDet(true);
   context.requestSequenceDet(true);

   // establish a context between peers

   byte[] inToken = new byte[0];
   byte[] outToken;

   // Loop while there still is a token to be processed

   while (!context.isEstablished()) {

       outToken = context.initSecContext(inToken, 0, inToken.length);

       // send the output token if generated
       if (outToken != null) {
           sendToken(outToken);
       }

       if (!context.isEstablished()) {
           inToken = readToken();
       }
   }

    // display context information
    System.out.println("Remaining lifetime in seconds = "
                                         + context.getLifetime());
    System.out.println("Context mechanism = " + context.getMech());
    System.out.println("Initiator = " + context.getSrcName());
    System.out.println("Acceptor = " + context.getTargName());

    if (context.getConfState()) {
        System.out.println("Confidentiality (i.e., privacy) is available");
    }

    if (context.getIntegState()) {
        System.out.println("Integrity is available");
    }

    // perform wrap on an application supplied message, appMsg,
    // using QOP = 0, and requesting privacy service
    byte[] appMsg = ...

    MessageProp mProp = new MessageProp(0, true);

    outToken = context.wrap(appMsg, 0, appMsg.length, mProp);

    sendToken(outToken);

    // perform unwrap on an incoming application message, and check
    // its privacy state and supplementary information
    inToken = readToken();

    mProp = new MessageProp(0, true);

    appMsg = context.unwrap(inToken, 0, inToken.length, mProp);

    System.out.println("Was it encrypted? " + mProp.getPrivacy());
    System.out.println("Duplicate Token? " + mProp.isDuplicateToken());
    System.out.println("Old Token? " + mProp.isOldToken());
    System.out.println("Unsequenced Token? " + mProp.isUnseqToken());
    System.out.println("Gap Token? " + mProp.isGapToken());

    // the application determines if the privacy state and supplementary
    // information are acceptable

    // release the local-end of the context
    context.dispose();