HMAC, GCM and Poly1305 are the common ones in use right now. In each case, these algorithms basically take the data as input, along with another key (an integrity key) and produce a MAC or a tag, which is just another piece of data that acts as a signature.
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The way we protect against this is to "pad" messages, to make large numbers of messages appear to be the same size no matter what. Military grade network encryption actually pads all traffic all the time, so it's always the same!
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Another problem with length is that if you're using compression, and let attackers control any of the content on a page that a user sees, that can let the attackers figure out even small secrets. Look up the "CRIME" attacks. It's awesome, and scary.
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I said the other problem is timing. Obviously the timing of each message is public, but is that a big deal? It can be! For example, if you send a message for every use keystroke, it's trivial to figure out what they're typing through timing analysis. WOW.
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Another example is VOIP. If your call app only sends data when people are speaking, but not during the silences, that's still enough to guess about 70% of English-language speech. Just from the silences! Scary cool.
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These examples underling: even when you use encryption algorithms and schemes we've been perfecting for about 80 years, there's still some gaps you can walk into and break the security. Which is why this stuff is worth knowing!
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Anyway, that's the level I'm going to stick at for now, but we've covered a lot of ground. If you've finished this thread, thank you! But also you should now have some kind of better understanding of what's going on, and what to be wary of. Feel free to AMA.
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Oh the truth table for XOR is wrong. I guess it's more of a lies table. Should be: a | b | c 0 | 0 | 0 1 | 0 | 1 0 | 1 | 1 1 | 1 | 0
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End of conversation
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