[freenet-dev] What we are really after was Re: Short refs was Re: alternative to #freenet-refs

[Florent Daignière]

* Matthew Toseland <toad at amphibian.dyndns.org> [2007-11-16 17:41:34]:

> On Friday 16 November 2007 17:07, Michael Rogers wrote:
> > Matthew Toseland wrote:
> > > Public key fingerprints are very difficult to turn into something that is 
> > > secure from all angles, and is short.
> > 
> > Fingerprint = hash of the public key. Comparable in length (though not
> > memorability) to a password, and more secure because it doesn't need to
> > be kept secret.
> 
> Well it *should* be kept secret, to prevent various harvesting attacks. But 
> yeah, the proposal seems sane. So, the remaining mechanisms:
> 
> Invites with a temporary keypair (invite = H(pubkey_temp), IP:port; 
> obfuscation key = H(pubkey_temp))
> 
> Short noderefs (ref = H(real_pubkey), IP:port; obfuscation key = H(pubkey_R + 
> H(pubkey_I)) )
> 
> And possibly SRP. 
> PRO: We can use easy-to-remember/communicate (low entropy) passphrases, rather 
> than 32 bytes (64 hex chars, 43 base64).
> PRO: And it's still secure, provided that we have a limited number of attempts 
> per password (so for SRP-based invites we will need IP:port, invite counter, 
> passphrase).
> SRP would normally be a one-way invite, but if the inviter is NATed Fred would 
> ask for the IP:port of the invitee.
> CON: How would we obfuscate it? Dictionary resistance requires that we don't 
> just send the password - SRP has a "username" aka invite counter so that it 
> can only allow a small number of attempts for a specific username/invite... 
> So we can't just superencrypt using the password!

And why not ? :) Use a few bytes of H(password)... Make it so small that
collisions are more than probable. He will end up with a hashcash to
solve... and SRP is gonna give him only a few tries.

Btw, if you generate passwords, you can be confident that they don't
figure in any dictionary ;)

NextGen$
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