Public Key Identification Based on the Equivalence of Quadratic Forms. - Rupert J. Hartung; Claus-Peter Schnorr (MFCS, 2007)

Cryptography Based on Quadratic Forms: Complexity Considerations. - Rupert J. Hartung (WEWoRC, 2007)

Identification and signatures based on NP-hard problems of indefinite quadratic forms. - Rupert J. Hartung; Claus-Peter Schnorr (J. Math. Cryptol., 2008)