[cryptography] PBKDF2 + current GPU or ASIC farms = game over for passwords (Re: TLS2)

Adam Back adam at cypherspace.org
Mon Sep 30 14:22:18 EDT 2013


On Mon, Sep 30, 2013 at 06:52:47PM +0100, Wasa wrote:
>>Also the PBKDF2 / scrypt happens on the client side - how do you think
>>your ARM powered smart phone will compare to a 9x 4096 core GPU monster. 
>>Not well :)
>
>How much would it help to delegate PBKDF2 / scrypt to smartphone GPU to
>break this asymmetry?

It might help a little in the right direction, and so probably should be
done; but I presume phone GPUs wont have that many cores nor high
performance to compare to an AMD 7990 (4096x 1Ghz cores) even if it
outperforms the phone CPU by a reasonable margin.

>since SRP and JPAKE use exponent_modulo sort of computation rather than a
>hash, any idea how this impacts attackers?  how well can you paralellize a
>dictionary brute force for DL problem?  I'm not expert so glad to hear
>about it.

The A part of AKE password amplification, means that you cant break it via
the DL stuff.  The password only authenticates the diffie-hellman like key
exchange, so it just is there to prevent MITM.  You still have a full 2048
bit DL or 256-bit ECDL to attack and that is hopeless.

The only attack is on the PBKDF2 stored on the server (or malware to grab
the password on the client)

>>Anyway and all that because we are seemingly alergic to using client side
>>keys which kill the password problem dead.  For people with smart phones
>>to hand all the time eg something like oneid.com (*) can avoid passwords
>>(split keys between smart phone and server, nothing on server to grind,
>>even stolen smart phone cant have its encrypted key store offline ground
>>to recover encrypted private keys (they are also split so you need to
>>compromise the server and the client simultaneously).  Also the user can
>>lock the account at any time in event of theft or device loss.
>
>i like the idea. Any issue/complications with re-provisioning or 
>multiple devices with same identity?

If you lose one device you can replace the device enrole it authenticated by
your other devices and securely restore access keys into it.  It does
support multiple devices, though each device also has a unique key as well
as a common identity key so that individual devices can be revoked instantly
if they are stolen.  It uses some fun crypto like a blind MAC to do split
key KDF and AKE type protocols.

They have a recovery mechanism also I think if you simultaneously lose all
our devices (laptop and smartphone) (user print out 128-bit key on
registration).  If the user doesnt do that they have to re-enrole as a new
identity with oneid and the relying parties.

I was thinking it could be a good tech for access to bitcoin online wallets
and exchanges because also the transaction details are displayed for
approval on the smart phone, so even if the laptop had bitcoin related
password targetted malware on it, you could still securely transact if you
read the transaction details on the smartphone before approving.

Adam


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