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.