Early work on cryptographically secure chains with timestamps was done by Haber and Stornetta, including their 1991 paper “How to Time-Stamp a Digital Document". Building upon their previous work, Haber, Stornetta and Bayer published “Improving the Efficiency and Reliability of Digital Time-Stamping", which incorporated consideration of costs and benefits of three methods of digital timestamping including; linear linking, random witness, and merkle trees. Massias, Avila, and Quisquater extend...