So there's an obvious (though imperfect) analogy between block ciphers and, say, HMAC. Imperfect because authentication always seems to involve metadata.
But is there a MAC analog to a stream cipher? That is, something where you can spend a few bits authenticating each frame of a movie, or sound sample, for example, and have some probabilistic chance of detecting alteration at each frame. I suppose it could also have uses with, say, an interactive SSH session, where each keystroke might be sent in its own packet. The closest thing I can think of is doing a truncated MAC on each frame. Looking at HMAC, it looks like you could leave the inner hash running while also finalizing it for each frame (assuming your library supports this), so that you could keep it open to feed the next frame to it - this allows each truncated MAC to attest to the authenticity of prior frames, which might or might not allow you to get by with fewer bits of MAC per frame in certain applications (details of which are complicated and not particularly germane to this query). -- I find your ideas intriguing and would like to subscribe to your newsletter. My emails do not have attachments; it's a digital signature that your mail program doesn't understand. | http://www.subspacefield.org/~travis/ If you are a spammer, please email j...@subspacefield.org to get blacklisted.
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