Inside Macintosh: Networking /

Chapter 5 - AppleTalk Data Stream Protocol (ADSP)

Using ASDSP

You can write an application that uses the AppleTalk Secure Data Stream Protocol (ASDSP) to

• open a secure ASDSP connection (sdspOpen)
• transmit encrypted data across a secure session (dspWrite using the encrypt flag)
• read data decrypted by ASDSP that was sent as encrypted across a secure session (dspRead)

The initiator end of your ASDSP client application must call the AOCE Authentication Manager to obtain credentials to pass on to ASDSP. ASDSP passes these credentials to the recipient end of the client application and uses them to establish a secure session in which the users of the client applications at both ends of the connection are positively identified. See "About ASDSP" beginning on page 5-9 for more information about this process. ASDSP client applications at either end of a connection can send data to each other that ASDSP encrypts for transmission and then decrypts before delivering it to the client at the receiving end.

An application that currently uses ADSP needs little modification to use ASDSP. To open an ASDSP connection, the client application at each end must issue the secure data stream protocol open routine (sdspOpen) instead of the standard open routine (dspOpen).
The sdspOpen routine uses a parameter block that, in addition to the standard ADSP parameters required to open a connection, contains the identity and credentials used in the challenge process; only the initiator end of the connection passes the credentials to ASDSP as input parameter values. The initiator and the recipient ends of a session each open the connection in a different manner:

• The initiator end of a session calls the sdspOpen routine using the request mode to direct ASDSP to open a connection with a specific socket.
• The recipient end of a session calls the sdspOpen routine in either passive mode or accept mode. A recipient end of a connection can be either of the following:
  • a specific socket that waits passively to receive an ASDSP connection request (the connection end associated with the socket calls the sdspOpen routine with a value of ocPassive for the ocMode parameter)
  • a connection listener that listens for connection requests and passes them on to a connection server (the connection listener calls the sdspOpen routine with a value of ocAccept for the ocMode parameter, and the connection server accepts and acknowledges receipt of a connection request)

You issue the sdspOpen routine by calling the Device Manager's PBControl function and passing it a pointer to the DSP parameter block for ASDSP that holds all of the input and output parameters for the call. The parameters that the sdspOpen call requires differ for the initiator and recipient ends of a connection. The next section describes how to open an ASDSP connection and how to send encrypted data across it.

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Subtopics

Opening a Secure Connection