Cryptography

With the catastrophes initiated by Stuxnet, Siemens S7 OpenSSL library vulnerabilites and the increasing attacks on SCADA networks these days, people are getting more and more cautious about the security loop holes in the present day systems and methods how to get rid of them.

One solution heard across is the utilization of Cryptography - public/private keys and digital signatures.

I was wondering whether some of you experts can provide more insight into the solution, as:

1. Is it possible on existing systems. If yes, how to implement it? My projects are using AB SLC-500 and Siemens S7-300 PLCs mainly.

2. Are there any PLC Products or interfaces available in the market to integrate with the existing systems?

3. Is there any better solution than the above mentioned?

Thanks in advance
Robin