Stream cipher support based upon JSSE.

The underlying SSLEngine has four ports: plaintext input/output and ciphertext input/output. These are modeled as a akka.stream.BidiShape element for use in stream topologies, where the plaintext ports are on the left hand side of the shape and the ciphertext ports on the right hand side.

Configuring JSSE is a rather complex topic, please refer to the JDK platform documentation or the excellent user guide that is part of the Play Framework documentation. The philosophy of this integration into Akka Streams is to expose all knobs and dials to client code and therefore not limit the configuration possibilities. In particular the client code will have to provide the SSLEngine, which is typically created from a SSLContext. Handshake parameters and other parameters are defined when creating the SSLEngine.

IMPORTANT NOTE

The TLS specification until version 1.2 did not permit half-closing of the user data session that it transports—to be precise a half-close will always promptly lead to a full close. This means that canceling the plaintext output or completing the plaintext input of the SslTls operator will lead to full termination of the secure connection without regard to whether bytes are remaining to be sent or received, respectively. Especially for a client the common idiom of attaching a finite Source to the plaintext input and transforming the plaintext response bytes coming out will not work out of the box due to early termination of the connection. For this reason there is a parameter that determines whether the SslTls operator shall ignore completion and/or cancellation events, and the default is to ignore completion (in view of the client–server scenario). In order to terminate the connection the client will then need to cancel the plaintext output as soon as all expected bytes have been received. When ignoring both types of events the operator will shut down once both events have been received. See also TLSClosing. For now, half-closing is also not supported with TLS 1.3 where the spec allows it.