Identification and authentication

 

The primary purpose of a security exit is to enable the MCA at each end of a channel to authenticate its partner. At each end of a message channel, and at the server end of an MQI channel, an MCA typically acts on behalf of the queue manager to which it is connected. At the client end of an MQI channel, an MCA typically acts on behalf of the user of the WebSphere MQ client application. In this situation, mutual authentication actually takes place between two queue managers, or between a queue manager and the user of a WebSphere MQ client application.

The supplied security exit (the SSPI channel exit) illustrates how mutual authentication can be implemented by exchanging authentication tokens that are generated, and subsequently checked, by a trusted authentication server such as Kerberos. For more details, see The SSPI channel exit program.

Mutual authentication can also be implemented by using Public Key Infrastructure (PKI) technology. Each security exit generates some random data, signs it using the private key of the queue manager or user it is representing, and sends the signed data to its partner in a security message. The partner security exit performs the authentication by checking the digital signature using the public key of the queue manager or user. Before exchanging digital signatures, the security exits might need to agree the algorithm for generating a message digest, if more than one algorithm is available for use.

When a security exit sends the signed data to its partner, it also needs to send some means of identifying the queue manager or user it is representing. This might be a Distinguished Name, or even a digital certificate. If a digital certificate is sent, the partner security exit can validate the certificate by working through the certificate chain to the root CA certificate. This provides assurance of the ownership of the public key that is used to check the digital signature.

The partner security exit can validate a digital certificate only if it has access to a key repository that contains the remaining certificates in the certificate chain. If a digital certificate for the queue manager or user is not sent, one must be available in the key repository to which the partner security exit has access. The partner security exit cannot check the digital signature unless it can find the signer's public key.

The Secure Sockets Layer (SSL) uses PKI techniques similar to ones just described. For more information about how the Secure Sockets Layer performs authentication, see Secure Sockets Layer (SSL) concepts.

If a trusted authentication server or PKI support is not available, other techniques can be used. A common technique, which can be implemented in security exits, uses a symmetric key algorithm.

One of the security exits, exit A, generates a random number and sends it in a security message to its partner security exit, exit B. Exit B encrypts the number using its copy of a key which is known only to the two security exits. Exit B sends the encrypted number to exit A in a security message with a second random number that exit B has generated. Exit A verifies that the first random number has been encrypted correctly, encrypts the second random number using its copy of the key, and sends the encrypted number to exit B in a security message. Exit B then verifies that the second random number has been encrypted correctly. During this exchange, if either security exit is not satisfied with the authenticity of other, it can instruct the MCA to close the channel.

An advantage of this technique is that no key or password is sent over the communications connection during the exchange. A disadvantage is that it does not provide a solution to the problem of how to distribute the shared key in a secure way. One solution to this problem is described in Confidentiality. A similar technique is used in SNA for the mutual authentication of two LUs when they bind to form a session. The technique is described in Session level authentication.

All the preceding techniques for mutual authentication can be adapted to provide one way authentication.

 

Parent topic:

Security exit

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