javax.net.ssl.SSLEngine

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A class which enables secure communications using protocols such as the Secure Sockets Layer (SSL) or IETF RFC 2246 "Transport Layer Security" (TLS) protocols, but is transport independent.

The secure communications modes include:

  Integrity Protection.  SSL/TLS protects against
 modification of messages by an active wiretapper.

  Authentication.  In most modes, SSL/TLS provides
 peer authentication.  Servers are usually authenticated, and
 clients may be authenticated as requested by servers.

  Confidentiality (Privacy Protection).  In most
 modes, SSL/TLS encrypts data being sent between client and
 server.  This protects the confidentiality of data, so that
 passive wiretappers won't see sensitive data such as financial
 information or personal information of many kinds.

These kinds of protection are specified by a "cipher suite", which is a combination of cryptographic algorithms used by a given SSL connection. During the negotiation process, the two endpoints must agree on a cipher suite that is available in both environments. If there is no such suite in common, no SSL connection can be established, and no data can be exchanged.

The cipher suite used is established by a negotiation process called "handshaking". The goal of this process is to create or rejoin a "session", which may protect many connections over time. After handshaking has completed, you can access session attributes by using the getSession() method.

The SSLSocket class provides much of the same security functionality, but all of the inbound and outbound data is automatically transported using the underlying Socket, which by design uses a blocking model. While this is appropriate for many applications, this model does not provide the scalability required by large servers.

The primary distinction of an SSLEngine is that it operates on inbound and outbound byte streams, independent of the transport mechanism. It is the responsibility of the SSLEngine user to arrange for reliable I/O transport to the peer. By separating the SSL/TLS abstraction from the I/O transport mechanism, the SSLEngine can be used for a wide variety of I/O types, such as non-blocking I/O (polling), selectable non-blocking I/O, Socket and the traditional Input/OutputStreams, local ByteBuffers or byte arrays, future asynchronous I/O models , and so on.

At a high level, the SSLEngine appears thus:

              app data

           |           ^
           |     |     |
           v     |     |
      ----+-----|-----+----+
      |          |          |
      |       SSL|Engine    |

wrap() | | | unwrap() | OUTBOUND | INBOUND | | | | ----+-----|-----+----+ | | ^ | | | v |

              net data

Application data (also known as plaintext or cleartext) is data which is produced or consumed by an application. Its counterpart is network data, which consists of either handshaking and/or ciphertext (encrypted) data, and destined to be transported via an I/O mechanism. Inbound data is data which has been received from the peer, and outbound data is destined for the peer.

(In the context of an SSLEngine, the term "handshake data" is taken to mean any data exchanged to establish and control a secure connection. Handshake data includes the SSL/TLS messages "alert", "change_cipher_spec," and "handshake.")

There are five distinct phases to an SSLEngine.

 Creation - The SSLEngine has been created and
initialized, but has not yet been used.  During this phase, an
application may set any SSLEngine-specific settings
(enabled cipher suites, whether the SSLEngine should
handshake in client or server mode, and so on).  Once
handshaking has begun, though, any new settings (except
client/server mode, see below) will be used for
the next handshake.

 Initial Handshake - The initial handshake is a procedure by
which the two peers exchange communication parameters until an
SSLSession is established.  Application data can not be sent during
this phase.

 Application Data - Once the communication parameters have
been established and the handshake is complete, application data
may flow through the SSLEngine.  Outbound
application messages are encrypted and integrity protected,
and inbound messages reverse the process.

  Rehandshaking - Either side may request a renegotiation of
the session at any time during the Application Data phase.  New
handshaking data can be intermixed among the application data.
Before starting the rehandshake phase, the application may
reset the SSL/TLS communication parameters such as the list of
enabled ciphersuites and whether to use client authentication,
but can not change between client/server modes.  As before, once
handshaking has begun, any new SSLEngine
configuration settings will not be used until the next
handshake.

  Closure - When the connection is no longer needed, the
application should close the SSLEngine and should
send/receive any remaining messages to the peer before
closing the underlying transport mechanism.  Once an engine is
closed, it is not reusable:  a new SSLEngine must
be created.

An SSLEngine is created by calling SSLContext.createSSLEngine() from an initialized SSLContext. Any configuration parameters should be set before making the first call to wrap(), unwrap(), or beginHandshake(). These methods all trigger the initial handshake.

Data moves through the engine by calling wrap() or unwrap() on outbound or inbound data, respectively. Depending on the state of the SSLEngine, a wrap() call may consume application data from the source buffer and may produce network data in the destination buffer. The outbound data may contain application and/or handshake data. A call to unwrap() will examine the source buffer and may advance the handshake if the data is handshaking information, or may place application data in the destination buffer if the data is application. The state of the underlying SSL/TLS algorithm will determine when data is consumed and produced.

Calls to wrap() and unwrap() return an SSLEngineResult which indicates the status of the operation, and (optionally) how to interact with the engine to make progress.

The SSLEngine produces/consumes complete SSL/TLS packets only, and does not store application data internally between calls to wrap()/unwrap(). Thus input and output ByteBuffers must be sized appropriately to hold the maximum record that can be produced. Calls to SSLSession.getPacketBufferSize() and SSLSession.getApplicationBufferSize() should be used to determine the appropriate buffer sizes. The size of the outbound application data buffer generally does not matter. If buffer conditions do not allow for the proper consumption/production of data, the application must determine (via SSLEngineResult) and correct the problem, and then try the call again.

For example, unwrap() will return a SSLEngineResult.Status.BUFFER_OVERFLOW result if the engine determines that there is not enough destination buffer space available. Applications should call SSLSession.getApplicationBufferSize() and compare that value with the space available in the destination buffer, enlarging the buffer if necessary. Similarly, if unwrap() were to return a SSLEngineResult.Status.BUFFER_UNDERFLOW, the application should call SSLSession.getPacketBufferSize() to ensure that the source buffer has enough room to hold a record (enlarging if necessary), and then obtain more inbound data.

SSLEngineResult r = engine.unwrap(src, dst); switch (r.getStatus()) { BUFFER_OVERFLOW: // Could attempt to drain the dst buffer of any already obtained // data, but we'll just increase it to the size needed. int appSize = engine.getSession().getApplicationBufferSize(); ByteBuffer b = ByteBuffer.allocate(appSize dst.position()); dst.flip(); b.put(dst); dst = b; // retry the operation. break; BUFFER_UNDERFLOW: int netSize = engine.getSession().getPacketBufferSize(); // Resize buffer if needed. if (netSize > dst.capacity()) { ByteBuffer b = ByteBuffer.allocate(netSize); src.flip(); b.put(src); src = b; } // Obtain more inbound network data for src, // then retry the operation. break; // other cases: CLOSED, OK. }

Unlike SSLSocket, all methods of SSLEngine are non-blocking. SSLEngine implementations may require the results of tasks that may take an extended period of time to complete, or may even block. For example, a TrustManager may need to connect to a remote certificate validation service, or a KeyManager might need to prompt a user to determine which certificate to use as part of client authentication. Additionally, creating cryptographic signatures and verifying them can be slow, seemingly blocking.

For any operation which may potentially block, the SSLEngine will create a Runnable delegated task. When SSLEngineResult indicates that a delegated task result is needed, the application must call getDelegatedTask() to obtain an outstanding delegated task and call its run() method (possibly using a different thread depending on the compute strategy). The application should continue obtaining delegated tasks until no more exist, and try the original operation again.

At the end of a communication session, applications should properly close the SSL/TLS link. The SSL/TLS protocols have closure handshake messages, and these messages should be communicated to the peer before releasing the SSLEngine and closing the underlying transport mechanism. A close can be initiated by one of: an SSLException, an inbound closure handshake message, or one of the close methods. In all cases, closure handshake messages are generated by the engine, and wrap() should be repeatedly called until the resulting SSLEngineResult's status returns "CLOSED", or isOutboundDone() returns true. All data obtained from the wrap() method should be sent to the peer.

closeOutbound() is used to signal the engine that the application will not be sending any more data.

A peer will signal its intent to close by sending its own closure handshake message. After this message has been received and processed by the local SSLEngine's unwrap() call, the application can detect the close by calling unwrap() and looking for a SSLEngineResult with status "CLOSED", or if isInboundDone() returns true. If for some reason the peer closes the communication link without sending the proper SSL/TLS closure message, the application can detect the end-of-stream and can signal the engine via closeInbound() that there will no more inbound messages to process. Some applications might choose to require orderly shutdown messages from a peer, in which case they can check that the closure was generated by a handshake message and not by an end-of-stream condition.

There are two groups of cipher suites which you will need to know about when managing cipher suites:

  Supported cipher suites:  all the suites which are
 supported by the SSL implementation.  This list is reported
 using getSupportedCipherSuites().

  Enabled cipher suites, which may be fewer than
 the full set of supported suites.  This group is set using the
 setEnabledCipherSuites(String []) method, and
 queried using the getEnabledCipherSuites() method.
 Initially, a default set of cipher suites will be enabled on a
 new engine that represents the minimum suggested
 configuration.

Implementation defaults require that only cipher suites which authenticate servers and provide confidentiality be enabled by default. Only if both sides explicitly agree to unauthenticated and/or non-private (unencrypted) communications will such a cipher suite be selected.

Each SSL/TLS connection must have one client and one server, thus each endpoint must decide which role to assume. This choice determines who begins the handshaking process as well as which type of messages should be sent by each party. The method setUseClientMode(boolean) configures the mode. Once the initial handshaking has started, an SSLEngine can not switch between client and server modes, even when performing renegotiations.

Applications might choose to process delegated tasks in different threads. When an SSLEngine is created, the current AccessControlContext is saved. All future delegated tasks will be processed using this context: that is, all access control decisions will be made using the context captured at engine creation.

Concurrency Notes: There are two concurrency issues to be aware of:

 The wrap() and unwrap() methods
 may execute concurrently of each other.

  The SSL/TLS protocols employ ordered packets.
 Applications must take care to ensure that generated packets
 are delivered in sequence.  If packets arrive
 out-of-order, unexpected or fatal results may occur.

 For example:



         synchronized (outboundLock) {
             sslEngine.wrap(src, dst);
             outboundQueue.put(dst);
         }

 As a corollary, two threads must not attempt to call the same method
 (either wrap() or unwrap()) concurrently,
 because there is no way to guarantee the eventual packet ordering.

A class which enables secure communications using protocols such as
the Secure Sockets Layer (SSL) or
 IETF RFC 2246 "Transport
Layer Security" (TLS)  protocols, but is transport independent.

The secure communications modes include:

      Integrity Protection.  SSL/TLS protects against
     modification of messages by an active wiretapper.

      Authentication.  In most modes, SSL/TLS provides
     peer authentication.  Servers are usually authenticated, and
     clients may be authenticated as requested by servers.

      Confidentiality (Privacy Protection).  In most
     modes, SSL/TLS encrypts data being sent between client and
     server.  This protects the confidentiality of data, so that
     passive wiretappers won't see sensitive data such as financial
     information or personal information of many kinds.



These kinds of protection are specified by a "cipher suite", which
is a combination of cryptographic algorithms used by a given SSL
connection.  During the negotiation process, the two endpoints must
agree on a cipher suite that is available in both environments.  If
there is no such suite in common, no SSL connection can be
established, and no data can be exchanged.

The cipher suite used is established by a negotiation process called
"handshaking".  The goal of this process is to create or rejoin a
"session", which may protect many connections over time.  After
handshaking has completed, you can access session attributes by
using the getSession() method.

The SSLSocket class provides much of the same security
functionality, but all of the inbound and outbound data is
automatically transported using the underlying Socket, which by design uses a blocking model.
While this is appropriate for many applications, this model does not
provide the scalability required by large servers.

The primary distinction of an SSLEngine is that it
operates on inbound and outbound byte streams, independent of the
transport mechanism.  It is the responsibility of the
SSLEngine user to arrange for reliable I/O transport to
the peer.  By separating the SSL/TLS abstraction from the I/O
transport mechanism, the SSLEngine can be used for a
wide variety of I/O types, such as non-blocking I/O (polling), selectable non-blocking I/O, Socket and the
traditional Input/OutputStreams, local ByteBuffers or byte arrays,  future asynchronous
I/O models , and so on.

At a high level, the SSLEngine appears thus:



                  app data

               |           ^
               |     |     |
               v     |     |
          ----+-----|-----+----+
          |          |          |
          |       SSL|Engine    |
  wrap()  |          |          |  unwrap()
          | OUTBOUND | INBOUND  |
          |          |          |
          ----+-----|-----+----+
               |     |     ^
               |     |     |
               v           |

                  net data
Application data (also known as plaintext or cleartext) is data which
is produced or consumed by an application.  Its counterpart is
network data, which consists of either handshaking and/or ciphertext
(encrypted) data, and destined to be transported via an I/O
mechanism.  Inbound data is data which has been received from the
peer, and outbound data is destined for the peer.

(In the context of an SSLEngine, the term "handshake
data" is taken to mean any data exchanged to establish and control a
secure connection.  Handshake data includes the SSL/TLS messages
"alert", "change_cipher_spec," and "handshake.")

There are five distinct phases to an SSLEngine.


     Creation - The SSLEngine has been created and
    initialized, but has not yet been used.  During this phase, an
    application may set any SSLEngine-specific settings
    (enabled cipher suites, whether the SSLEngine should
    handshake in client or server mode, and so on).  Once
    handshaking has begun, though, any new settings (except
    client/server mode, see below) will be used for
    the next handshake.

     Initial Handshake - The initial handshake is a procedure by
    which the two peers exchange communication parameters until an
    SSLSession is established.  Application data can not be sent during
    this phase.

     Application Data - Once the communication parameters have
    been established and the handshake is complete, application data
    may flow through the SSLEngine.  Outbound
    application messages are encrypted and integrity protected,
    and inbound messages reverse the process.

      Rehandshaking - Either side may request a renegotiation of
    the session at any time during the Application Data phase.  New
    handshaking data can be intermixed among the application data.
    Before starting the rehandshake phase, the application may
    reset the SSL/TLS communication parameters such as the list of
    enabled ciphersuites and whether to use client authentication,
    but can not change between client/server modes.  As before, once
    handshaking has begun, any new SSLEngine
    configuration settings will not be used until the next
    handshake.

      Closure - When the connection is no longer needed, the
    application should close the SSLEngine and should
    send/receive any remaining messages to the peer before
    closing the underlying transport mechanism.  Once an engine is
    closed, it is not reusable:  a new SSLEngine must
    be created.

An SSLEngine is created by calling SSLContext.createSSLEngine() from an initialized
SSLContext.  Any configuration
parameters should be set before making the first call to
wrap(), unwrap(), or
beginHandshake().  These methods all trigger the
initial handshake.

Data moves through the engine by calling wrap() or unwrap() on outbound or inbound data, respectively.  Depending on
the state of the SSLEngine, a wrap() call
may consume application data from the source buffer and may produce
network data in the destination buffer.  The outbound data
may contain application and/or handshake data.  A call to
unwrap() will examine the source buffer and may
advance the handshake if the data is handshaking information, or
may place application data in the destination buffer if the data
is application.  The state of the underlying SSL/TLS algorithm
will determine when data is consumed and produced.

Calls to wrap() and unwrap() return an
SSLEngineResult which indicates the status of the
operation, and (optionally) how to interact with the engine to make
progress.

The SSLEngine produces/consumes complete SSL/TLS
packets only, and does not store application data internally between
calls to wrap()/unwrap().  Thus input and output
ByteBuffers must be sized appropriately to hold the
maximum record that can be produced.  Calls to SSLSession.getPacketBufferSize() and SSLSession.getApplicationBufferSize() should be used to determine
the appropriate buffer sizes.  The size of the outbound application
data buffer generally does not matter.  If buffer conditions do not
allow for the proper consumption/production of data, the application
must determine (via SSLEngineResult) and correct the
problem, and then try the call again.

For example, unwrap() will return a SSLEngineResult.Status.BUFFER_OVERFLOW result if the engine
determines that there is not enough destination buffer space available.
Applications should call SSLSession.getApplicationBufferSize()
and compare that value with the space available in the destination buffer,
enlarging the buffer if necessary.  Similarly, if unwrap()
were to return a SSLEngineResult.Status.BUFFER_UNDERFLOW, the
application should call SSLSession.getPacketBufferSize() to ensure
that the source buffer has enough room to hold a record (enlarging if
necessary), and then obtain more inbound data.



  SSLEngineResult r = engine.unwrap(src, dst);
  switch (r.getStatus()) {
  BUFFER_OVERFLOW:
      // Could attempt to drain the dst buffer of any already obtained
      // data, but we'll just increase it to the size needed.
      int appSize = engine.getSession().getApplicationBufferSize();
      ByteBuffer b = ByteBuffer.allocate(appSize  dst.position());
      dst.flip();
      b.put(dst);
      dst = b;
      // retry the operation.
      break;
  BUFFER_UNDERFLOW:
      int netSize = engine.getSession().getPacketBufferSize();
      // Resize buffer if needed.
      if (netSize > dst.capacity()) {
          ByteBuffer b = ByteBuffer.allocate(netSize);
          src.flip();
          b.put(src);
          src = b;
      }
      // Obtain more inbound network data for src,
      // then retry the operation.
      break;
  // other cases: CLOSED, OK.
  }


Unlike SSLSocket, all methods of SSLEngine are
non-blocking.  SSLEngine implementations may
require the results of tasks that may take an extended period of
time to complete, or may even block.  For example, a TrustManager
may need to connect to a remote certificate validation service,
or a KeyManager might need to prompt a user to determine which
certificate to use as part of client authentication.  Additionally,
creating cryptographic signatures and verifying them can be slow,
seemingly blocking.

For any operation which may potentially block, the
SSLEngine will create a Runnable
delegated task.  When SSLEngineResult indicates that a
delegated task result is needed, the application must call getDelegatedTask() to obtain an outstanding delegated task and
call its run() method (possibly using
a different thread depending on the compute strategy).  The
application should continue obtaining delegated tasks until no more
exist, and try the original operation again.

At the end of a communication session, applications should properly
close the SSL/TLS link.  The SSL/TLS protocols have closure handshake
messages, and these messages should be communicated to the peer
before releasing the SSLEngine and closing the
underlying transport mechanism.  A close can be initiated by one of:
an SSLException, an inbound closure handshake message, or one of the
close methods.  In all cases, closure handshake messages are
generated by the engine, and wrap() should be repeatedly
called until the resulting SSLEngineResult's status
returns "CLOSED", or isOutboundDone() returns true.  All
data obtained from the wrap() method should be sent to the
peer.

closeOutbound() is used to signal the engine that the
application will not be sending any more data.

A peer will signal its intent to close by sending its own closure
handshake message.  After this message has been received and
processed by the local SSLEngine's unwrap()
call, the application can detect the close by calling
unwrap() and looking for a SSLEngineResult
with status "CLOSED", or if isInboundDone() returns true.
If for some reason the peer closes the communication link without
sending the proper SSL/TLS closure message, the application can
detect the end-of-stream and can signal the engine via closeInbound() that there will no more inbound messages to
process.  Some applications might choose to require orderly shutdown
messages from a peer, in which case they can check that the closure
was generated by a handshake message and not by an end-of-stream
condition.

There are two groups of cipher suites which you will need to know
about when managing cipher suites:


      Supported cipher suites:  all the suites which are
     supported by the SSL implementation.  This list is reported
     using getSupportedCipherSuites().

      Enabled cipher suites, which may be fewer than
     the full set of supported suites.  This group is set using the
     setEnabledCipherSuites(String []) method, and
     queried using the getEnabledCipherSuites() method.
     Initially, a default set of cipher suites will be enabled on a
     new engine that represents the minimum suggested
     configuration.


Implementation defaults require that only cipher suites which
authenticate servers and provide confidentiality be enabled by
default.  Only if both sides explicitly agree to unauthenticated
and/or non-private (unencrypted) communications will such a
cipher suite be selected.

Each SSL/TLS connection must have one client and one server, thus
each endpoint must decide which role to assume.  This choice determines
who begins the handshaking process as well as which type of messages
should be sent by each party.  The method setUseClientMode(boolean) configures the mode.  Once the initial
handshaking has started, an SSLEngine can not switch
between client and server modes, even when performing renegotiations.

Applications might choose to process delegated tasks in different
threads.  When an SSLEngine
is created, the current AccessControlContext
is saved.  All future delegated tasks will be processed using this
context:  that is, all access control decisions will be made using the
context captured at engine creation.



Concurrency Notes:
There are two concurrency issues to be aware of:


     The wrap() and unwrap() methods
     may execute concurrently of each other.

      The SSL/TLS protocols employ ordered packets.
     Applications must take care to ensure that generated packets
     are delivered in sequence.  If packets arrive
     out-of-order, unexpected or fatal results may occur.

     For example:



             synchronized (outboundLock) {
                 sslEngine.wrap(src, dst);
                 outboundQueue.put(dst);
             }

     As a corollary, two threads must not attempt to call the same method
     (either wrap() or unwrap()) concurrently,
     because there is no way to guarantee the eventual packet ordering.

javax.net.ssl.SSLEngine

begin-handshakeclj

close-inboundclj

close-outboundclj

get-delegated-taskclj

get-enable-session-creation?clj

get-enabled-cipher-suitesclj

get-enabled-protocolsclj

get-handshake-sessionclj

get-handshake-statusclj

get-need-client-auth?clj

get-peer-hostclj

get-peer-portclj

get-sessionclj

get-ssl-parametersclj

get-supported-cipher-suitesclj

get-supported-protocolsclj

get-use-client-mode?clj

get-want-client-auth?clj

inbound-done?clj

outbound-done?clj

set-enable-session-creationclj

set-enabled-cipher-suitesclj

set-enabled-protocolsclj

set-need-client-authclj

set-ssl-parametersclj

set-use-client-modeclj

set-want-client-authclj

unwrapclj

wrapclj

begin-handshake^clj

close-inbound^clj

close-outbound^clj

get-delegated-task^clj

get-enable-session-creation?^clj

get-enabled-cipher-suites^clj

get-enabled-protocols^clj

get-handshake-session^clj

get-handshake-status^clj

get-need-client-auth?^clj

get-peer-host^clj

get-peer-port^clj

get-session^clj

get-ssl-parameters^clj

get-supported-cipher-suites^clj

get-supported-protocols^clj

get-use-client-mode?^clj

get-want-client-auth?^clj

inbound-done?^clj

outbound-done?^clj

set-enable-session-creation^clj

set-enabled-cipher-suites^clj

set-enabled-protocols^clj

set-need-client-auth^clj

set-ssl-parameters^clj

set-use-client-mode^clj

set-want-client-auth^clj

unwrap^clj

wrap^clj