1993-08-25 - Blinding messages (newbie questions)

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From: nobody@shell.portal.com
To: cypherpunks@toad.com
Message Hash: 875d25f4da9c549251fd8c7a26dab11969a03e74751bf28e662c845e3b11c8be
Message ID: <9308250839.AA20717@jobe.shell.portal.com>
Reply To: N/A
UTC Datetime: 1993-08-25 10:36:33 UTC
Raw Date: Wed, 25 Aug 93 03:36:33 PDT

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From: nobody@shell.portal.com
Date: Wed, 25 Aug 93 03:36:33 PDT
To: cypherpunks@toad.com
Subject: Blinding messages (newbie questions)
Message-ID: <9308250839.AA20717@jobe.shell.portal.com>
MIME-Version: 1.0
Content-Type: text/plain

>[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?