Trusted timestamping is the process of securely keeping track of the creation and modification time of a document. Security here means that no one—not even the owner of the document—should be able to change it once it has been recorded provided that the timestamper's integrity is never compromised. The administrative aspect involves setting up a publicly available, trusted timestamp management infrastructure to collect, process and renew timestamps. History The idea of timestamping information is centuries old. For example, when Robert Hooke discovered Hooke's law in 1660, he did not want to publish it yet, but wanted to be able to claim priority. So he published the anagram ceiiinosssttuv and later published the translation ut tensio sic vis (Latin for "as is the extension, so is the force"). Similarly, Galileo first published his discovery of the phases of Venus in the anagram form. Sir Isaac Newton, in responding to questions from Leibniz in a letter in 1677, concealed the details of his "fluxional technique" with an anagram: The foundations of these operations is evident enough, in fact; but because I cannot proceed with the explanation of it now, I have preferred to conceal it thus: 6accdae13eff7i3l9n4o4qrr4s8t12ux. On this foundation I have also tried to simplify the theories which concern the squaring of curves, and I have arrived at certain general Theorems. Trusted digital timestamping has first been discussed in literature by Stuart Haber and W. Scott Stornetta. Classification There are many timestamping schemes with different security goals: PKI-based – timestamp token is protected using PKI digital signature. Linking-based schemes – timestamp is generated in such a way that it is related to other timestamps. Distributed schemes – timestamp is generated in cooperation of multiple parties. Transient key scheme – variant of PKI with short-living signing keys. MAC – simple secret key based scheme, found in ANSI ASC X9.95 Standard. Database – document hashes are stored in trusted archive; there is online lookup service for verification. Hybrid schemes – the linked and signed method is prevailing, see X9.95. Coverage in standards: For systematic classification and evaluation of timestamping schemes see works by Masashi Une. Trusted (digital) timestamping According to the RFC 3161 standard, a trusted timestamp is a timestamp issued by a Trusted Third Party (TTP) acting as a Time Stamping Authority (TSA). It is used to prove the existence of certain data before a certain point (e.g. contracts, research data, medical