Blinding messages (newbie questions)

[nobody@shell.portal.com]

>[Karl Barrus describes blinding]

Excellent post!  Can you tolerate a few newbie questions?

> Conceptually, when you blind a message, nobody else can read it. 

So "blinding" is a synonym for encryption with your own public
key, aka multiplication by a very-hard-to-factor number?

> under the right circumstances if another 
> party digitally signs a blinded message, the unblinded message will 
> contain a valid digital signature.

In other words if Alice encrypts and Bob signs, Da(Db(Ea(M))) = Db(M)?  
Under what conditions?  Does RSA (in PGP) satisfy those conditions?

> If someone asks
> you to digitally sign a random stream of symbols, remember that what you
> sign may be unblinded to reveal a contract, etc. 

For what applications would Bob want to sign an encrypted contract
instead of a plaintext?