From: Anonymous <nobody@replay.com>
Date: Wed, 28 Oct 1998 08:14:36 +0800
To: cypherpunks@cyberpass.net
Subject: Re: Using a password as a private key.
Message-ID: <199810272341.AAA20410@replay.com>
MIME-Version: 1.0
Content-Type: text/plain



RedRook@yahoo.com writes:
> Assymetic crypto systems such as Diffie-Hellman, El-Gamel, and DSS,
> allow the private key to be a randomly chosen number. But, as a cute
> hack, instead of using a random number, for the private key, you could
> use a hash of the User Name, and a password.
> 
> Doing so allows the users to generate their private key on demand.
> They don't have to store the private key, and if they want to work on
> a another computer, they don't need to bring along a copy.  Has any one
> tried this? Is there existing software that does this? Any comments on
> the security of such a scheme?  The only draw back that I can think of
> is the potential lack of randomness in the key. If the user chooses a
> bad password, it would be possible to brute force the public key.

You can accomplish the same thing by encrypting your private key (including
RSA) with a passphrase and publishing it.

Because of the problems with passphrase bruting, it probably only
makes sense to do this with a machine-generated passphrase which has
guaranteed entropy.  Something like: "Aarhous mocrader Fals paca rate
portion wiserustingned" has a guaranteed > 128 bits of entropy, which
should be enough for most purposes.  Probably with an hour's study most
people could memorize such a passphrase.