Revocation of cryptographic keys by way of a blockchain-based banknote

User computer system for revoking a first asymmetric key pair of another user computer system using a banknote,

• wherein the first asymmetric key pair comprises a first private cryptographic key and a first public cryptographic key,
• wherein the first asymmetric key pair is assigned to a first blockchain address in a blockchain,
• wherein the user computer system comprises a processor and a memory with program instructions,
• wherein for the first asymmetric key pair an assignment to the banknote is further registered in the blockchain, which is signed using a banknote-individual second private cryptographic key of a banknote-individual second asymmetric key pair of the banknote,
• wherein the banknote comprises a security element with a processor and a memory with program instructions,
• wherein an identification number uniquely identifying the banknote is stored in the memory,
• wherein the second private cryptographic key is stored in a protected memory area of the memory,
• wherein the second asymmetric key pair is assigned to a banknote-individual second blockchain address in the blockchain,
• wherein execution of the program instructions of the user computer system by the processor causes the processor to control the user computer system to revoke the first asymmetric key pair, wherein the revoking comprises:
• sending a revocation request to revoke the first asymmetric key pair from the user computer system to the banknote,
• in response to the revocation request, receiving a cryptogram signed using the second private cryptographic key from the banknote by the user computer system, the cryptogram comprising the identification number of the banknote and a revocation confirmation of the banknote,
• forwarding the signed cryptogram by the user computer system to a blockchain server of the blockchain for entering the revocation confirmation of the banknote identified by the identification number into the blockchain, the entry of the revocation confirmation revoking the first asymmetric key pair and, as a result of the revocation,
• blocking entries of transactions into the blockchain whose releases are based on a signature using the revoked first private cryptographic key.

Banknote for revoking a first asymmetric key pair of a first user computer system using a second user computer system, the first asymmetric key pair comprising a first private cryptographic key and a first public cryptographic key, wherein the first asymmetric key pair is assigned to a first blockchain address in a blockchain,

• wherein an assignment to the banknote is further registered in the blockchain for the first asymmetric key pair, which assignment is signed using a banknote-individual second private cryptographic key of a banknote-individual second asymmetric key pair of the banknote,
• wherein the banknote comprises a security element with a processor and a memory with program instructions,
• wherein an identification number uniquely identifying the banknote is stored in the memory,
• wherein the second private cryptographic key is stored in a protected memory area of the memory,
• wherein the second asymmetric key pair is assigned to a banknote-individual second blockchain address in the blockchain,
• wherein execution of the program instructions of the banknote by the processor causes the processor to control the banknote to revoke the first asymmetric key pair,
• wherein revoking comprises:
• receiving, by the banknote, a revocation request to revoke the first asymmetric key pair from the second user computer system,
• generating a cryptogram signed using the second private cryptographic key from the banknote by the banknote, the cryptogram comprising the identification number of the banknote and a revocation confirmation of the banknote,
• in response to the revocation request, sending the signed cryptogram from the banknote to the second user computer system for forwarding to a blockchain server of the blockchain for entering the revocation confirmation of the banknote identified by the identification number into the blockchain, the entry of the revocation confirmation revoking the first asymmetric key pair and, as a result of the revocation,
• blocking entries of transactions into the blockchain whose releases are based on a signature using the revoked first private cryptographic key.