David Chaum has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).
Abstract: Numbers standing for cash money can be spent only one time each, otherwise the account from which they were withdrawn would be revealed. More generally, a technique for issuing and showing blind digital signatures ensures that if they are shown responsive to different challenges, then certain information their signer ensures they contain will be revealed and can be recovered efficiently. Some embodiments allow the signatures to be unconditionally untraceable if shown no more than once. Extensions allow values to be encoded in the signatures when they are shown, and for change on unshown value to be obtained in a form that is aggregated and untraceable.
Abstract: A payer party obtains from a signer party by a blind signature system a first public key digital signature having a first value in a withdrawal transaction; the payer reduces the value of the first signature obtained from the first value to a second value and provides this reduced-value form of the signature to the signer in a payment transaction; the signer returns a second digital signature to the payer by a blind signature system in online consummation of the payment transaction; the paper derives from the first and the second signature a third signature having a value increased corresponding to the magnitude of the difference between the first and the second values.
Abstract: Cryptographic methods and apparatus for forming, checking, blinding, and unblinding of undeniable signatures are disclosed. The validity of such signatures is based on public keys and they are formed by a signing party with access to a corresponding private key, much as with public key digital signatures. A difference is that whereas public key digital signatures can be checked by anyone using the corresponding public key, the validity of undeniable signatures is in general checked by a protocol conducted between a checking party and the signing party. During such a protocol, the signing party may improperly try to deny the validity of a valid signature, but the checking party will be able to detect this with substantially high probability. In case the signing party is not improperly performing the protocol, the checking party is further able to determine with high probability whether or not the signature validly corresponds to the intended message and public key.
Abstract: A user controlled card computer C and communicating tamper-resistant part T are disclosed that conduct secure transactions with an external system S. All communication between T and S is moderated by C, who is able to prevent T and S from leaking any message or pre-arranged signals to each other. Additionally, S can verify that T is in immediate physical proximity. Even though S receives public key digital signatures through C that are checkable using public keys whose corresponding private keys are known only to a unique T, S is unable to learn which transactions involve which T. It is also possible for S to allow strictly limited messages to be communicated securely between S and T.
Abstract: Numbers standing for cash money can be spent only one time each, otherwise the account from which they were withdrawn would be revealed. More generally, a technique for issuing and showing blind digital signatures ensures that if they are shown responsive to different challanges, then certain information their signer ensures they contain will be revealed and can be recovered efficiently. Some embodiments allow the signatures to be unconditionally untraceable if shown no more than once. Extensions allow values to be encoded in the signatures when they are shown, and for change on unshown value to be obtained in a form that is aggregated and untraceable.
Abstract: The invention provides a cryptographic apparatus which may be "personalized" to its owner. The apparatus may be utilized by its owner to identify himself to an external computer system, to perform various financial transactions with an external system, and to provide various kinds of credentials to an external system. The apparatus, in one embodiment, is separable into a cryptographic device, packaged in a tamper resistant housing, and a personal terminal device. The cryptographic device includes interface circuitry to permit information exchange with the external system, a memory device for storage of data necessary to allow identification of the owner, and control logic for controlling the exchange of data with the external system to identify the owner. Certain data which must be utilized to perform the identification information exchange is stored in the memory device in encrypted form. The decryption of this data requires the entry of a secret ID, known to the owner.