Align behaviour of CTR and SIC modes in the JCE API.

[timw]

CTR and SIC are implemented with the same underlying engine, so make their behaviour in the JCE API consistent (previously SIC would fail on 64 bit block ciphers, while CTR would not).

[bcgit]

We had a bit of a discussion about this, but we can't make use of this patch.

I know this is going to sound bizarre (or maybe just old fashioned) but there's a reason for the difference.

Originally SIC was specified as being available for only 128 bit block ciphers or greater (in some document that I can no longer find) this is why if you specify SIC it requires it, if you specify CTR it doesn't. It may sound a bit pedantic but this also means that if you see the use of SIC in BC you are certain the algorithm has a 128 bit or greater block size - this kind of certainty does mean something to some people (auditors for one example...). I'm aware that a look at Wikipedia will tell me that I'm probably one of the few people on the planet that is aware of this, but as we've established a "contract" on this one already, it seems best we keep it this way, as people may be relying on this in some fashion.

[timw]

Yeah, I suspected this might have 'mysterious' origins :) Forgot to mention that in the pull request.