Test that the encrypted payloads are uniform. #374
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payjoin/src/hpke.rs
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| /// For each of the 256 pairwise combinations, ensure their lengths are equal, |
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there are 256 ordered pairs, but XOR is commutative... you correctly implemented only distinct unordered, so my original count is wrong.
| /// For each of the 256 pairwise combinations, ensure their lengths are equal, | |
| /// For each of the (n choose 2) = n*(n-1)/2 combinations, ensure their lengths are equal, |
For what it's worth the reasoning behind these values is that in a uniformly random bit string for each bit position there's a
payjoin/src/hpke.rs
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| assert!( | ||
| accumulator.iter().all(|&b| b != 0), |
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Another approach would be to check that all bits (as opposed to bytes) contain variation. For this check the number of messages in the set should be 80 or 128 or whatever instead of 16 in order to have negligible chance of false positive.
| accumulator.iter().all(|&b| b != 0), | |
| accumulator.iter().any(|&b| b != 0xff), |
edit: previous suggestion was incorrect, comparing to 1 instead of 0xff
DanGould
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This randomized test will generate a false negative with negligible probability if all encrypted messages share an identical byte at a given position by chance. It should fail deterministically if any bit position has a fixed value.
close #371
This randomized test will generate a false negative with negligible probability
if all encrypted messages share an identical byte at a given position by chance.
It should fail deterministically if any bit position has a fixed value.
re #364 (review) from @nothingmuch
I did check that this test would indeed fail before the ellswift changes by cherry-picking the test on 9c4880c