Monitoring system for monitoring hash-based digital signatures

A monitoring apparatus for monitoring hash-based digital signatures, comprising:

• an interface unit configured to:
• receive a signature request data structure comprising data to be digitally signed from the requesting device;
• store the data to be signed;
• receive a hash-based digital signature generated for the data to be signed by a stateful hash-based cryptographic function of a signing device;
• and
• a key evaluation unit configured to:
• extract a one-time signature from the received hash-based digital signature;
• determine a one-time public key based on the stored data to be signed and the one-time signature;
• compare the one-time public key with previous one-time public keys determined from hash-based digital signatures previously received from the signing device;
• and
• if the one-time public key is different to any of previous one-time public keys, store the one-time public key in a data storage unit;
• and
• if the one-time public key is equal to at least one of the previous one-time public keys, output a first warning signal to the requesting device.

A method for monitoring hash-based digital signatures comprising:

• receiving a signature request data structure comprising data to be digitally signed from the requesting device;
• storing the data to be signed;
• receiving a hash-based digital signature generated for the data to be signed by a stateful hash-based cryptographic function of the signing device;
• extracting a one-time signature from the received hash-based digital signature;
• determining a one-time public key based on the stored data to be signed and the one-time signature;
• comparing the one-time public key with previous one-time public keys determined from hash-based digital signatures previously received from the signing device;
• and
• if the one-time public key is different to any of previous one-time public keys, storing the one-time public key in a data storage unit, and
• if the one-time public key is equal to at least one of the previous one-time public keys, outputting a first warning signal to the requesting device.