Cryptographically Strong Undeniable Signatures, Unconditionally Secure for the Signer. - David Chaum; Eugène van Heijst; Birgit Pfitzmann (CRYPTO, 1991)

New Constructions of Fail-Stop Signatures and Lower Bounds (Extended Abstract). - Eugène van Heijst; Torben P. Pedersen; Birgit Pfitzmann (CRYPTO, 1992)