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Comment by whatnotests | Hacker News Reader

Using something unchangeable (such as one's retina) to derive a key for encryption sounds like a great idea, until the key must change.

You can't change your retina so easily.

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The problem is that you don't want something too unchangeable because if the derived key is somehow discovered (or you get your retina scanned when entering a country -- which happens in Australia, the US, Japan and quite a few other places) then you cannot change your keys and you're stuck with useless keys. To resolve this you have to devolves it an elaborate PBKDF using your retina as a salt.

Personally I really dislike the concept of identity-based crypto, mainly because it make anonymity much harder. Keybase is very clever in how they attempt to solve the identity-based problem, but I'm not convinced if it actually makes this any more secure than just using WoT.

And then there's the part where people lose or damage fingers or retinas. Accidents happen. Your crypto may not be the first thing that comes to mind when you suffer injury, but it's a real problem in any population large enough.

Not only that... everyone in the street can see your eye, and high quality photo's might provide enough data to leak the key without you knowing. Same goes for stuff like fingerprints, you leave them everywhere you go.

Edit: typo

The exactly implementation doesn't seem clear, but looks to my uneducated eye like this is still an oracle, but one that could be replicated rather than requiring key escrow with an intermediate knowing the keys. I'd assume that you could add salt & pepper (as with password generators) to create new keys... but then you would still have to pass those to the oracle (e.g. using the oracle's public key, which you could reasonably know) and trust the oracle to generate them correctly.

Like password generators you could have many public keys (eg one for each recipient's public key and an advertised pepper that increments with each message) from your single biometric or even including adress, time, or place.

I just don't see how any oracle that you don't control access to isn't susceptible to compromise. I also don't see how the biometric is better than a memorized public key (or salt) other than you can't lose it, since spoofing the biometric will still be possible.

Correct me if I'm off base here.

The key (literally and figuratively) is in the trust of the biometric reader.

Some people can

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