Blind signatures

A "blind signature" is a digital signature where the signer does not know what he signs.

??? That is stupid thing to do!??

Solution: use cut-and-choose:

• Person gives, say, 100 "encrypted" messages to signer.
• Signer chooses 1 at random.
• Person gives the decryption key for the other 99.
• Signer signs the remaining one "blind".