Fine-grained forward-secure signature scheme

A method comprising providing a signature value on a message in a network of connected computer nodes, the method being executable by a first computer node and the step of providing comprising the steps of:

• selecting a first signature element;
• selecting a signature exponent value from a number of exponent values;
• and
• deriving a second signature element from a provided secret cryptographic key, the message, and the number of exponent values such that the first signature element, the second signature element, and the signature exponent value satisfy a known relationship with the message and a provided public cryptographic key, wherein the signature value comprises the first signature element, the second signature element, and a signature reference to the signature exponent value,
• the signature value being sendable within the network to a second computer node for verification.

A method comprising verifying signature value on a message in a network of connected computer nodes, the method being executable by a second computer node and the step of verifying comprising the steps of:

• receiving the signature value from a first computer node;
• deriving a signature exponent value from the signature value;
• and
• verifying whether the signature exponent value and part of the signature value satisfy a known relationship with the message and a provided public cryptographic key, otherwise refusing the signature value,
• wherein the signature value was generated from a first signature element, a number of exponent values, a provided secret cryptographic key, and the message.