Kerckhoffs' principle is that security should not depend on secrecy, apart from the key. Social security number is not a key - at least not in the sense understood by cryptographers. Another form of Kerckhoff's principle is Shannon's Maxim: "the enemy knows the system".
Gunnar Peterson uses a chess analogy for service-oriented security. The message is the king, and if you are not using WS-Security (and apparently only 28% of ESBs do) then it's WS-GameOver. This can be seen as another application of Kerckhoffs' principle: you don't make SOA secure by trying to obscure your web services - this just compromises reuse without actually improving security. You protect the payload not the design.
But what exactly is the payload here - the information or the transaction? By Cowan's argument, it may seem a waste of effort to protect the information. But of course if you are a commercial organization (say), you can't just leak people's private data with the excuse that everyone else is doing it so it's not worth protecting. The point is that you must protect the transaction as well, just in case the information is leaking somewhere else in the network.
Cowan thinks it is a good idea to provide a diverse set of security policies and mechanisms to the user. (See also his post on Doomsday Hackers and Evildoing Robots.) This supports my own belief in differentiated security.
UpdateNot just commercial organizations leaking private data. See Henry Porter's comments in the Observer (Surveillance is really getting under my skin) about the ease with which the RFID chip on the new UK passport can be cracked, together with the casual unconcern of Governnment officials. FishNChipPapers comments:
"It is naive to believe ... you can build impregnable systems. Instead our government should be focusing on approaches, such as distributed, federated databases, lack of a common identifier to link into those databases etc to mitigate the very real risks."Meanwhile, in his response to David Cowan, Chris Walsh asks whether the problem (together with the value of Cowan's investment) might be eliminated by legislation, "with a stroke of the pen". But I think Chris has answered this question himself by quoting Gerry Goffin and Carole King in the title of his post - "It's Too Late Baby".
Wikipedia: Differentiated security, Kerckhoffs' principle
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