• Improving the availability of time-stamping servicesAnsper, A.; Buldas, Ahto; Saarepera, Märt; Willemson, JanInformation Security and Privacy : 6th Australian Conference : ACISP 2001 : Sydney, Australia, July 11-13, 2001 : proceedings2001 / p. 360-375 https://link.springer.com/chapter/10.1007/3-540-47719-5_29