Patent ID: 7640432

Claim:
A method of providing anonymous digital cash, the method comprising: providing an entity with a secure co-processor; a user establishing a secure channel to a program running on said coprocessor; the user sending an unsigned coin to be digitally signed to the coprocessor using any secure digital signature algorithm; and said co-processor forming a copy of the unsigned coin; signing the unsigned coin with a non-homomorphic signature; and said co-processor encrypting the signed coin and encrypting the copy of the unsigned coin using a public key of a given encryption scheme having said public key and a private key; sending back to the user both the encrypted copy of the signed coin and the encrypted copy of the unsigned coin, the user having the private key of said given encryption scheme, wherein the user then using said private key to decrypt both the signed and unsigned copies of the coin, and using the pair of signed and unsigned copies of the coin as a unit as digital cash for payment to a recipient while keeping the identity of the user unknown to the coprocessor.