Non-transferable anonymous digital receipts

A system for verifying ownership of an electronic receipt by a validating party (B) in a communication system providing a public key infrastructure, the verification arising out of a series of messages being sent and received between a first party (U), a second party (A), and a certificate authority (A), the system comprising:

• a memory storage device;
• a processor device in communication with said memory storage device at a first computer system configured to perform a method to:
• receive, at the certificate authority (A) a request message (RM) from the first party (U), the request message (RM) comprising a transaction request (TR) and a public key (PU) based on a secret (SU) owned by the first party (U), and wherein the secret (SU) is associated with at least a further secret (SU) of a further public key (PU) of the first party (U),
• electronically sign, by said certificate authority (A), at least part of the request message (RM) with a public key (PA) assigned to said the certificate authority (A) for issuance as said electronic receipt (LU) to said first party (U);
• said method further comprising:
• subsequently receive, at said second party (A), an encryption (E2) of the secret (SU) of a user's public key (PU) under the further public key (PU);
• publish, by said second party (A), said encryption (E2) to establish a link between the further secret (SU) of the further public key (PU) and the secret (SU) of the public key (PU), wherein:
• E2=encpu(S);
• and
• receive at said validation party (B) a proof message (PM) from said first party (U), said PM derived from said further public key (PU) based on the further secret (SU) owned by the user U, said further secret (SU) being associated via said encryption (E2) to said further public key (PU), said proof message (PM) being further derived from an electronic receipt (LU) previously issued by second party (A) signing said RM with a public key PA of said second party;
• said second validating party (B) receiving said encryption (E2) and publishing said encryption E2;
• and
• a processor device in communication with a memory storage device at a second computer system configured to perform a method to:
• validate by the validating party (B) user ownership of said electronic receipt (LU) and (LU) and said encryption (E2) by verifying a cryptographic proof of the existence of values PU, SU, LU, PU, SU, LU such that the value PU is a first public key derived from the value SU and the value LU is a signature with respect to the public key PA on at least the value (PU), and the value PU is the public key derived from the value SU and the value LU is a signature with respect to the public key EA on at least the value PU and the encryption E2 is the encryption of the value SU under the value PU.

An article of manufacture comprising:

• a computer usable medium, said medium not a propagating signal, said medium having computer readable program code tangibly embodied therein to execute at least one machine instruction in a processing unit for verifying ownership of an electronic receipt by a validating party (B) in a communication system providing a public key infrastructure, the verification arising out of a series of messages being sent and received between a first party (U), a second party (A), and a certificate authority (A) wherein:
• a certificate authority (A) receives a request message (RM) from the first party (U), the request message (RM) comprising a transaction request (TR) and a public key (PU) based on a secret (SU) owned by the first party (U), and wherein the secret (SU) is associated with at least a further secret (SU) of a further public key (PU) of the first party (U),
• the certificate authority (A) electronically signs at least part of the request message (RM) with a public key (PA) assigned to said the certificate authority (A) for issuance as said electronic receipt (LU) to said first party (U);
• and wherein
• a second party (A) subsequently receives an encryption (E2) of the secret (SU) of a user's public key (PU) under the further public key (PU), the second party (A) publishing said encryption (E2) to establish a link between the further secret (SU) of the further public key (PU) and the secret (SU) of the public key (PU), wherein:
• E2=encpu(SU);
• and
• wherein at the processing unit, when running, said computer readable program code causing the processing unit to perform a method to:
• receive at said validation party (B) a proof message (PM) from said first party (U), said PM derived from said further public key (PU) based on the further secret (SU) owned by the user U, said further secret (SU) being associated via said encryption (E2) to said further public key (PU), said proof message (PM) being further derived from an electronic receipt (LU) previously issued by second party (A) signing said RM with a public key PA of said second party;
• said second validating party (B) receiving said encryption (E2) and publishing said encryption E2;
• and
• validate by the validating party (B) user ownership of said electronic receipt (LU) and (LU) and said encryption (E2) by verifying a cryptographic proof of the existence of values PU, SU, LU, PU, SU, LU such that the value PU is a first public key derived from the value SU and the value LU is a signature with respect to the public key PA on at least the value (PU), and the value PU is the public key derived from the value SU and the value LU is a signature with respect to the public key PA on at least the value PU and the encryption E2 is the encryption of the value SU under the value PU.