I was just wondering if there was a "great answer" floating around that I can refer people to when they discuss using unauthenticated encryption across an untrusted (and thus possibly-malicious) space?

Something along the lines of "Why should I use Authenticated Encryption instead of just encryption"? (Preferably in the symmetric case)

UPDATE - Question started as: Why should I use Authenticated Encryption instead of just encryption?

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2 Answers 2

I can't remember seeing a question that would actually provide a related, general reference. Checking http://crypto.stackexchange.com/search?q=Authenticated+Encryption+%09is%3Aquestion didn't really show any usable Q&A either.

But you could post that question to create a related reference-point yourself. It has been done before (for example: “Why should I make my cipher public?” and “What is the ideal cipher model?”).

From my point of view, your question “"Why should I use Authenticated Encryption instead of just encryption?” would indeed be a nice reference-point to have. Besides that, the question itself obviously hasn't been asked yet… so I don't think you would lose anything by asking.

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My nomination for the closest I've seen to a canonical answer would be: Don't use encryption without message authentication

Disclaimer: I'm biased (I wrote it). Also, FYI, it is on Security.SE rather than on this site. I don't know if it answers what you wanted; it explains why you need some kind of authentication, but not so much why to use AE instead of Encrypt-then-MAC (for instance).

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Well Encrypt-then-MAC is AE, and I wasn't envisaging an article about how to choose an AE scheme since that's more situation dependent. So, that would be reasonable enough, although personally I'd prefer an answer with more detail on why you need to authenticate (nb: definitely not saying my answer does that!). –  figlesquidge Dec 7 '13 at 10:39
    
Would you mind porting that answer over onto the question here? I could do it as community-wiki, but given it's your answer then you definitely have (a) rights to the content and (b) deserve the credit it may get –  figlesquidge Apr 1 at 13:00
    
@figlesquidge, I'm not clear on what the benefit of doing that would be. I can see only downsides (e.g., that they get out of sync). I don't think that link is going to rot (if Security.SE goes away then probably Crypto.SE will be gone too). –  D.W. Apr 2 at 3:46
    
Fair enough. In that case, do I/we/you post a link-only answer or a comment linking to it –  figlesquidge Apr 2 at 7:42

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