RFC 8353
Generic Security Service API Version 2: Java Bindings Update
7.4. public interface GSSContext
This interface encapsulates the GSS-API security context and provides the security services (wrap, unwrap, getMIC, and verifyMIC) 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 its tokens between peers. Before the context establishment phase is initiated, the context initiator may request specific characteristics desired of the established context. These can be set using the set methods. After the context is established, the caller can check the actual characteristic and services offered by the context using the query methods. The context establishment phase begins with the first call to the init method by the context initiator. During this phase, the initSecContext and acceptSecContext methods will produce GSS-API authentication tokens, which the calling application needs to send to its peer. If an error occurs at any point, an exception will get thrown and the code will start executing in a catch block where the exception may contain an output token that should be sent to the peer for debugging or informational purpose. If not, the normal flow of code continues, and the application can make a call to the isEstablished() method. If this method returns "false", it indicates that a token is needed from its peer in order to continue the context establishment phase. A return value of "true" signals that the local end of the context is established. This may still require that a token be sent to the peer, if one is produced by GSS-API. During the context establishment phase, the isProtReady() method may be called to determine if the context can be used for the per-message operations. This allows applications to use per-message operations on contexts that aren't 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.7.4.1. Static Constants
public static final int DEFAULT_LIFETIME A lifetime constant representing the default context lifetime. The value of this constant is 0.
public static final int INDEFINITE_LIFETIME A lifetime constant representing indefinite context lifetime. The value of this constant is the maximum integer value in Java -- Integer.MAX_VALUE.7.4.2. initSecContext
public byte[] initSecContext(byte[] inputBuf, int offset, int len) throws GSSException Called by the context initiator to start the context creation process. This method MAY return an output token that the application will need to send to the peer for processing by the accept call. The application can call isEstablished() to determine if the context establishment phase is complete for this peer. A return value of "false" from isEstablished() indicates that more tokens are expected to be supplied to the initSecContext() method. Note that it is possible that the initSecContext() method will return a token for the peer and isEstablished() will return "true" also. This indicates that the token needs to be sent to the peer, but the local end of the context is now fully established. Upon completion of the context establishment, the available context options may be queried through the get methods. A GSSException will be thrown if the call fails. Users SHOULD call its getOutputToken() method to find out if there is a token that can be sent to the acceptor to communicate the reason for the error. Parameters: inputBuf Token generated by the peer. This parameter is ignored on the first call. offset The offset within the inputBuf where the token begins. len The length of the token within the inputBuf (starting at the offset).7.4.3. acceptSecContext
public byte[] acceptSecContext(byte[] inTok, int offset, int len) throws GSSException Called by the context acceptor upon receiving a token from the peer.
This method MAY return an output token that the application will need
to send to the peer for further processing by the init call.
The "null" return value indicates that no token needs to be sent to
the peer. The application can call isEstablished() to determine if
the context establishment phase is complete for this peer. A return
value of "false" from isEstablished() indicates that more tokens are
expected to be supplied to this method.
Note that it is possible that acceptSecContext() will return a token
for the peer and isEstablished() will return "true" also. This
indicates that the token needs to be sent to the peer, but the local
end of the context is now fully established.
Upon completion of the context establishment, the available context
options may be queried through the get methods.
A GSSException will be thrown if the call fails. Users SHOULD call
its getOutputToken() method to find out if there is a token that can
be sent to the initiator to communicate the reason for the error.
Parameters:
inTok Token generated by the peer.
offset The offset within the inTok where the token
begins.
len The length of the token within the inTok
(starting at the offset).
7.4.4. isEstablished
public boolean isEstablished()
Used during context establishment to determine the state of the
context. Returns "true" if this is a fully established context on
the caller's side and no more tokens are needed from the peer.
Should be called after a call to initSecContext() or
acceptSecContext() when no GSSException is thrown.
7.4.5. dispose
public void dispose() throws GSSException
Releases any system resources and cryptographic information stored in
the context object. This will invalidate the context.
7.4.6. getWrapSizeLimit
public int getWrapSizeLimit(int qop, boolean confReq, int maxTokenSize) throws GSSException Returns the maximum message size that, if presented to the wrap method with the same confReq and qop parameters, will result in an output token containing no more than the maxTokenSize bytes. This call is intended for use by applications that communicate over protocols that impose a maximum message size. It enables the application to fragment messages prior to applying protection. GSS-API implementations are RECOMMENDED but not required to detect invalid QOP values when getWrapSizeLimit is called. This routine guarantees only a maximum message size, not the availability of specific QOP values for message protection. Successful completion of this call does not guarantee that wrap will be able to protect a message of the computed length, since this ability may depend on the availability of system resources at the time that wrap is called. However, if the implementation itself imposes an upper limit on the length of messages that may be processed by wrap, the implementation SHOULD NOT return a value that is greater than this length. Parameters: qop Indicates the level of protection wrap will be asked to provide. confReq Indicates if wrap will be asked to provide privacy service. maxTokenSize The desired maximum size of the token emitted by wrap.7.4.7. wrap
public byte[] wrap(byte[] inBuf, int offset, int len, MessageProp msgProp) throws GSSException Applies per-message security services over the established security context. The method will return a token with a cryptographic MIC and MAY optionally encrypt the specified inBuf. The returned byte array will contain both the MIC and the message.
The MessageProp object is instantiated by the application and used to
specify a QOP value that selects cryptographic algorithms and a
privacy service to optionally encrypt the message. The underlying
mechanism that is used in the call may not be able to provide the
privacy service. It sets the actual privacy service that it does
provide in this MessageProp object, which the caller SHOULD then
query upon return. If the mechanism is not able to provide the
requested QOP, it throws a GSSException with the BAD_QOP code.
Since some application-level protocols may wish to use tokens emitted
by wrap to provide "secure framing", implementations SHOULD support
the wrapping of zero-length messages.
The application will be responsible for sending the token to the
peer.
Parameters:
inBuf Application data to be protected.
offset The offset within the inBuf where the data
begins.
len The length of the data within the inBuf (starting
at the offset).
msgProp Instance of MessageProp that is used by the
application to set the desired QOP and privacy
state. Set the desired QOP to 0 to request the
default QOP. Upon return from this method, this
object will contain the actual privacy state that
was applied to the message by the underlying
mechanism.
7.4.8. unwrap
public byte[] unwrap(byte[] inBuf, int offset, int len,
MessageProp msgProp) throws GSSException
Used by the peer application to process tokens generated with the
wrap call. The method will return the message supplied in the peer
application to the wrap call, verifying the embedded MIC.
The MessageProp object is instantiated by the application and is used
by the underlying mechanism to return information to the caller such
as the QOP, whether confidentiality was applied to the message, and
other supplementary message state information.
Since some application-level protocols may wish to use tokens emitted
by wrap to provide "secure framing", implementations SHOULD support
the wrapping and unwrapping of zero-length messages.
Parameters:
inBuf GSS-API wrap token received from peer.
offset The offset within the inBuf where the token
begins.
len The length of the token within the inBuf
(starting at the offset).
msgProp Upon return from the method, this object will
contain the applied QOP, the privacy state of the
message, and supplementary information, described
in Section 5.12.3, stating whether the token was
a duplicate, old, out of sequence, or arriving
after a gap.
7.4.9. getMIC
public byte[] getMIC(byte[] inMsg, int offset, int len,
MessageProp msgProp) throws GSSException
Returns a token containing a cryptographic MIC for the supplied
message for transfer to the peer application. Unlike wrap, which
encapsulates the user message in the returned token, only the message
MIC is returned in the output token.
Note that privacy can only be applied through the wrap call.
Since some application-level protocols may wish to use tokens emitted
by getMIC to provide "secure framing", implementations SHOULD support
derivation of MICs from zero-length messages.
Parameters:
inMsg Message over which to generate MIC.
offset The offset within the inMsg where the token
begins.
len The length of the token within the inMsg
(starting at the offset).
msgProp Instance of MessageProp that is used by the
application to set the desired QOP. Set the
desired QOP to 0 in msgProp to request the
default QOP. Alternatively, pass in "null" for
msgProp to request default QOP.
7.4.10. verifyMIC
public void verifyMIC(byte[] inTok, int tokOffset, int tokLen,
byte[] inMsg, int msgOffset, int msgLen,
MessageProp msgProp) throws GSSException
Verifies the cryptographic MIC, contained in the token parameter,
over the supplied message.
The MessageProp object is instantiated by the application and is used
by the underlying mechanism to return information to the caller such
as the QOP indicating the strength of protection that was applied to
the message and other supplementary message state information.
Since some application-level protocols may wish to use tokens emitted
by getMIC to provide "secure framing", implementations SHOULD support
the calculation and verification of MICs over zero-length messages.
Parameters:
inTok Token generated by peer's getMIC method.
tokOffset The offset within the inTok where the token
begins.
tokLen The length of the token within the inTok
(starting at the offset).
inMsg Application message over which to verify the
cryptographic MIC.
msgOffset The offset within the inMsg where the message
begins.
msgLen The length of the message within the inMsg
(starting at the offset).
msgProp Upon return from the method, this object will
contain the applied QOP and supplementary
information, described in Section 5.12.3, stating
whether the token was a duplicate, old, out of
sequence, or arriving after a gap. The
confidentiality state will be set to "false".
7.4.11. export
public byte[] export() throws GSSException
Provided to support the sharing of work between multiple processes.
This routine will typically be used by the context acceptor, in an
application where a single process receives incoming connection
requests and accepts security contexts over them, then passes the
established context to one or more other processes for message
exchange.
This method deactivates the security context and creates an inter-
process token that, when passed to the byte array constructor of the
GSSContext interface in another process, will re-activate the context
in the second process. Only a single instantiation of a given
context may be active at any one time; a subsequent attempt by a
context exporter to access the exported security context will fail.
The implementation MAY constrain the set of processes by which the
inter-process token may be imported, either as a function of local
security policy or as a result of implementation decisions. For
example, some implementations may constrain contexts to be passed
only between processes that run under the same account, or which are
part of the same process group.
The inter-process token MAY contain security-sensitive information
(for example, cryptographic keys). While mechanisms are encouraged
either to avoid placing such sensitive information within inter-
process tokens or to encrypt the token before returning it to the
application, in a typical GSS-API implementation, this may not be
possible. Thus, the application MUST take care to protect the inter-
process token and ensure that any process to which the token is
transferred is trustworthy.
7.4.12. requestMutualAuth
public void requestMutualAuth(boolean state) throws GSSException
Sets the request state of the mutual authentication flag for the
context. This method is only valid before the context creation
process begins and only for the initiator.
Parameters:
state Boolean representing if mutual authentication
should be requested during context establishment.
7.4.13. requestReplayDet
public void requestReplayDet(boolean state) throws GSSException
Sets the request state of the replay detection service for the
context. This method is only valid before the context creation
process begins and only for the initiator.
Parameters:
state Boolean representing if replay detection is
desired over the established context.
7.4.14. requestSequenceDet
public void requestSequenceDet(boolean state) throws GSSException
Sets the request state for the sequence-checking service of the
context. This method is only valid before the context creation
process begins and only for the initiator.
Parameters:
state Boolean representing if sequence detection is
desired over the established context.
7.4.15. requestCredDeleg
public void requestCredDeleg(boolean state) throws GSSException
Sets the request state for the credential delegation flag for the
context. This method is only valid before the context creation
process begins and only for the initiator.
Parameters:
state Boolean representing if credential delegation is
desired.
7.4.16. requestAnonymity
public void requestAnonymity(boolean state) throws GSSException Requests anonymous support over the context. This method is only valid before the context creation process begins and only for the initiator. Parameters: state Boolean representing if anonymity support is requested.7.4.17. requestConf
public void requestConf(boolean state) throws GSSException Requests that confidentiality service be available over the context. This method is only valid before the context creation process begins and only for the initiator. Parameters: state Boolean indicating if confidentiality services are to be requested for the context.7.4.18. requestInteg
public void requestInteg(boolean state) throws GSSException Requests that integrity services be available over the context. This method is only valid before the context creation process begins and only for the initiator. Parameters: state Boolean indicating if integrity services are to be requested for the context.7.4.19. requestLifetime
public void requestLifetime(int lifetime) throws GSSException Sets the desired lifetime for the context in seconds. This method is only valid before the context creation process begins and only for the initiator. Use GSSContext.INDEFINITE_LIFETIME and GSSContext.DEFAULT_LIFETIME to request indefinite or default context lifetime.
Parameters: lifetime The desired context lifetime in seconds.7.4.20. setChannelBinding
public void setChannelBinding(ChannelBinding cb) throws GSSException Sets the channel bindings to be used during context establishment. This method is only valid before the context creation process begins. Parameters: cb Channel bindings to be used.7.4.21. getCredDelegState
public boolean getCredDelegState() Returns the state of the delegated credentials for the context. When issued before context establishment is completed or when the isProtReady method returns "false", it returns the desired state; otherwise, it will indicate the actual state over the established context.7.4.22. getMutualAuthState
public boolean getMutualAuthState() Returns the state of the mutual authentication option for the context. When issued before context establishment completes or when the isProtReady method returns "false", it returns the desired state; otherwise, it will indicate the actual state over the established context.7.4.23. getReplayDetState
public boolean getReplayDetState() Returns the state of the replay detection option for the context. When issued before context establishment completes or when the isProtReady method returns "false", it returns the desired state; otherwise, it will indicate the actual state over the established context.
7.4.24. getSequenceDetState
public boolean getSequenceDetState() Returns the state of the sequence detection option for the context. When issued before context establishment completes or when the isProtReady method returns "false", it returns the desired state; otherwise, it will indicate the actual state over the established context.7.4.25. getAnonymityState
public boolean getAnonymityState() Returns "true" if this is an anonymous context. When issued before context establishment completes or when the isProtReady method returns "false", it returns the desired state; otherwise, it will indicate the actual state over the established context.7.4.26. isTransferable
public boolean isTransferable() throws GSSException Returns "true" if the context is transferable to other processes through the use of the export method. This call is only valid on fully established contexts.7.4.27. isProtReady
public boolean isProtReady() Returns "true" if the per-message operations can be applied over the context. Some mechanisms may allow the usage of per-message operations before the context is fully established. This will also indicate that the get methods will return actual context state characteristics instead of the desired ones.7.4.28. getConfState
public boolean getConfState() Returns the confidentiality service state over the context. When issued before context establishment completes or when the isProtReady method returns "false", it returns the desired state; otherwise, it will indicate the actual state over the established context.
7.4.29. getIntegState
public boolean getIntegState() Returns the integrity service state over the context. When issued before context establishment completes or when the isProtReady method returns "false", it returns the desired state; otherwise, it will indicate the actual state over the established context.7.4.30. getLifetime
public int getLifetime() Returns the context lifetime in seconds. When issued before context establishment completes or when the isProtReady method returns "false", it returns the desired lifetime; otherwise, it will indicate the remaining lifetime for the context.7.4.31. getSrcName
public GSSName getSrcName() throws GSSException Returns the name of the context initiator. This call is valid only after the context is fully established or the isProtReady method returns "true". It is guaranteed to return an MN.7.4.32. getTargName
public GSSName getTargName() throws GSSException Returns the name of the context target (acceptor). This call is valid only after the context is fully established or the isProtReady method returns "true". It is guaranteed to return an MN.7.4.33. getMech
public Oid getMech() throws GSSException Returns the mechanism OID for this context. This method MAY be called before the context is fully established, but the mechanism returned MAY change on successive calls in a negotiated mechanism case.
7.4.34. getDelegCred
public GSSCredential getDelegCred() throws GSSException Returns the delegated credential object on the acceptor's side. To check for availability of delegated credentials, call getDelegCredState. This call is only valid on fully established contexts.7.4.35. isInitiator
public boolean isInitiator() throws GSSException Returns "true" if this is the initiator of the context. This call is only valid after the context creation process has started.7.4.36. Example Code
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. <CODE BEGINS> GSSManager mgr = GSSManager.getInstance(); // start by creating the name for a service entity GSSName targetName = mgr.createName("service@host", GSSName.NT_HOSTBASED_SERVICE); // create a context using default credentials for the above entity // and the implementation-specific default mechanism GSSContext context = mgr.createContext(targetName, null, /* default mechanism */ null, /* default credentials */ GSSContext.INDEFINITE_LIFETIME); // set desired context options - all others are "false" by default context.requestConf(true); context.requestMutualAuth(true); context.requestReplayDet(true); context.requestSequenceDet(true); // establish a context between peers - using byte arrays byte[] inTok = new byte[0];
try {
do {
byte[] outTok = context.initSecContext(inTok, 0,
inTok.length);
// send the token if present
if (outTok != null)
sendToken(outTok);
// check if we should expect more tokens
if (context.isEstablished())
break;
// another token expected from peer
inTok = readToken();
} while (true);
} catch (GSSException e) {
print("GSSAPI error: " + e.getMessage());
// If the exception contains an output token,
// it should be sent to the acceptor.
byte[] outTok = e.getOutputToken();
if (outTok != null) {
sendToken(outTok);
}
return;
}
// display context information
print("Remaining lifetime in seconds = " + context.getLifetime());
print("Context mechanism = " + context.getMech().toString());
print("Initiator = " + context.getSrcName().toString());
print("Acceptor = " + context.getTargName().toString());
if (context.getConfState())
print("Confidentiality security service available");
if (context.getIntegState())
print("Integrity security service available");
// perform wrap on an application-supplied message, appMsg,
// using QOP = 0, and requesting privacy service
byte[] appMsg ...
MessageProp mProp = new MessageProp(0, true);
byte[] tok = context.wrap(appMsg, 0, appMsg.length, mProp);
if (mProp.getPrivacy())
print("Message protected with privacy.");
sendToken(tok);
// release the local end of the context
context.dispose();
<CODE ENDS>
(page 70 continued on part 6)
