Tamper-Evident Digital Signatures: Protecting Certification Authorities Against Malware

We introduce the notion of tamper-evidence for digital signature generation in order to defend against attacks aimed at covertly leaking secret information held by corrupted network nodes. This is achieved by letting observers (which need not be trusted) verify the absence of covert channels by means of techniques we introduce herein. We call our signature schemes tamper-evident since any deviation from the protocol is immediately detectable. We demonstrate our technique for RSA-PSS and DSA signature schemes and how the same technique can be applied to Feige-Fiat-Shamir (FFS) and Schnorr signature schemes. Our technique does not modify the distribution of the generated signature transcripts, and has only a minimal overhead in terms of computation, communication, and storage.