Method for creating a signal for time-stamping of documents (A), comprising the following steps: a) selecting a digitally stored reference document (D1-D3), which is a digital sample of the current state of a certain reference source at a certain first point in time, where the truthfulness of each reference document can be verified by consulting one or several publically available information sources concerning the historic state of said reference source; b) using the reference document as an input values to a one-way function, and calculating the corresponding output value; c) updating the signal based upon the said output value, so that the said output value (P1-P3) is constituted by or can be determined based upon the value of the signal; and d) repeating from a) using another digitally stored reference document which is a sample of the current state of the same or another reference source at a subsequent point in time.