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If we're talking about the actual hash signal uses for this value, then sure, but talking about the number of digits displayed isn't even the right thing to care about, since they're using SHA1 for the hash AFAICT: https://github.com/WhisperSystems/Signal-Android/blob/3.0.0/...

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SHA1? SHA1 SHA1‽ I'd always thought that OWS had incredibly good crypto — why are they using SHA1? If it's to support relatively short hashes … I just can't even.

There's simply no excuse to choose to use SHA1 in 2016. It's not completely broken, it's probably good enough, but why not just truncate SHA2?

SHA-1 is fine in this context. SHA-1 isn't as collision-resistant as it was once thought to be, but that's not a property that you care about for this use-case.

The same principle applies to checksums that are sometimes published for binaries - many still use MD5 or SHA-1 - and that's fine too, as (second) preimage resistance is what counts here, rather than collision-resistance.

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