Earlier today some folks published a paper that claims the SIMON cipher from the NSA has been broken, at least for the 32/64 variant. I've spent the last hour reading the paper, https://eprint.iacr.org/2019/474.pdf , there's some really strange things in there ...
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O.k. so https://www.gutenberg.org/cache/epub/10/pg10.txt … is 4,452,069 bytes long, that's 556,509 64-bit blocks. Should there really be some kind of analysis of Birthday bounds?pic.twitter.com/5y4ClVDcU3
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There's a few other typos, it says 54-bits in one place, for example. My point with these weirdnesses isn't that they are flat-out wrong, it's that they are imprecise and missing links, and if you just broke an encryption algorithm, it's not helpful to convince the reader!
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Btw "Alba" is just the Scottish Gaelic word for "Scotland" ... so Alba3 means "Scotland 3". The authors claim to be in Edinburgh, but they use "ize" suffixes throughout, like "optimize".
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I read it as: if you start with a plaintext and iterate over the keyspace, you cannot generate all of the ciphertext space, only some fraction of it
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Me too, but this obviously isn't true for a trivial insecure crappy counter example, but it's made as a general statement. There's no need for a long-winded explanation to establish that there are birthday bounds for ciphertext collisions. And the explanation isn't even precise!
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That one's pretty standard, assuming the cipher behaves as a random function. Not really a new result, tho.
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(I mean, random permutation, but if you only look at a single input then it's the same.)
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Presumably assuming a PRF.
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This number comes up quite a lot - its also how much a hash function contracts on each iteration. Probably for the same reason (too lazy to think about it right now). Perhaps unsurprisingly it is 1 - 1/e. :-)
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