Speaker: Bertram Poettering (Royal Holloway University of London, UK)
Dr. Bertram Poettering studied at universities in Hamburg (UHH) and Lisbon (UNL) and holds degrees in both Mathematics and Computer Science. Since he received his Ph.D. at the Technical University of Darmstadt in 2012, he holds a postdoctoral research position in the Information Security Group at Royal Holloway. His research is currently focused on the aspects of practical cryptography.
Title: Coercion-resistant digital signatures
Digital signatures are often used by trusted authorities to make unique bindings between a subject and a digital object; for example, certificate authorities certify a public key belongs to a domain name, and time-stamping authorities certify that a certain piece of information existed at a certain time.
Traditional digital signature schemes however impose no uniqueness conditions, so a trusted authority could be coerced to make multiple certifications for the same subject but different objects. In this talk we propose the notion of a double-authentication-preventing signature, in which a value to be signed is split into two parts: a subject and a message. If a signer ever signs two different messages for the same subject, enough information is revealed to allow anyone to compute valid signatures on behalf of the signer. This double-signature forgeability property discourages signers from misbehaving and gives signers some cryptographic arguments to resist coercion.