Digital signature schemes are often considered "in isolation" in cryptography. In practice, however, the same public key is often used for more than one scheme. Therefore classical security proofs do not apply.
This paper presents the first security proof for the important RSA-PSS and RSA-PKCS#1 v1.5 signature schemes that holds even if the same key pair is used for both schemes simultaneously.
This is a positive result that provides evidence that the re-use of keys, as done for instance by many Web servers on the Internet, is secure.