Re: [openpgp] Deriving an OpenPGP secret key from a human readable seed
Michael Richardson <mcr@sandelman.ca> Fri, 18 October 2019 06:53 UTC
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From: Michael Richardson <mcr@sandelman.ca>
To: Daniel Kahn Gillmor <dkg@fifthhorseman.net>, openpgp@ietf.org
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Comments: In-reply-to Daniel Kahn Gillmor <dkg@fifthhorseman.net> message dated "Thu, 17 Oct 2019 13:42:30 -0400."
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Date: Fri, 18 Oct 2019 08:54:12 +0200
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Subject: Re: [openpgp] Deriving an OpenPGP secret key from a human readable seed
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Daniel Kahn Gillmor <dkg@fifthhorseman.net> wrote: > yep, that's why i'm trying to help think this through, even though i'm > not particularly excited about it. :) >> {An interesting (mathematical, density of primes) question would be >> whether one would be able to determine from looking at the public key >> whether it was recoverable or not. That is, can one recognize some >> pattern in the expanded DRBG. It might still be statistically secure, >> yet since the amount of entropy in the key is less than the entropy in >> the input, it might leave a pattern} > Can you give an example of this? I haven't tried to prove this, but i > think if the generated public key (whether a curve25519 point or an RSA > modulus) is distinguishable from other public keys, there is a strong > argument to be made that either the DRBG or the secret key derivation > mechanism is deeply flawed. If I could prove such a thing then I'd have a Fields Medal for having discovered something new and interesting about the density of primes :-) If the input to our KDF is 120 bits and the output is 256 bits, then there must be a bunch of numbers that we can't derive from the KDF. But, as PHB says, 2^120 is a big enough work factor that it's okay. (5bits * 5 groups * 4 characters/group = 120) For ECDSA, any number will do, AFAIK. {When producing numbers RSA, I think we have to start with the random number and then search deterministically for a suitable prime. I was more thinking that this process might leave detectable traces} -- ] Never tell me the odds! | ipv6 mesh networks [ ] Michael Richardson, Sandelman Software Works | network architect [ ] mcr@sandelman.ca http://www.sandelman.ca/ | ruby on rails [
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- Re: [openpgp] Deriving an OpenPGP secret key from… Daniel Kahn Gillmor
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- Re: [openpgp] Deriving an OpenPGP secret key from… Kai Engert
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- Re: [openpgp] Deriving an OpenPGP secret key from… Kai Engert
- Re: [openpgp] Deriving an OpenPGP secret key from… Michael Richardson
- Re: [openpgp] Deriving an OpenPGP secret key from… Daniel Kahn Gillmor
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