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> Avoid: constructions with huge keys, cipher "cascades"

Can anyone please explain what's wrong with e.g. 4096 bit keys (instead of 1024 bit) and piling 2-3 different or same encryption passes? Performance implications are obvious; what are security implications?

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This is in the context of symmetric keys, so I'm guessing "huge keys" is a reference to the fact that "448-bit crypto" is a giant red flag because it screams "we're using blowfish".

See I just write 1/5th of a recommendation and leave it open-ended so Colin or 'pbsd can make it look like I was smart to begin with. Yeah... Blowfish... that's what I meant... :)

Well, in the more general case "huge symmetric keys" is a flag for "doesn't understand crypto", but 448-bit blowfish keys are the most common place I see this happening.

What is your opinion on Threefish then? Is there something fundamentally wrong with bigger keys/blocks, or is it just that known big key/block schemes are not useful?

Mostly it's just an indicator that the person doesn't understand the security concepts. If you believe a 4096 bit AES key will do you any good, there's probably other fundamental issues that you've misunderstood.

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