Eternal log file

A perpetual log file is a computer science process and is used to make manipulation of information almost impossible or to reveal any manipulations.

Use and functionality

To prove that data (a text) already existed in a certain form at a certain point in time, the data (or its checksum ) can be entered in the perpetual log file and the resulting hash value of the log file in another medium that is sufficiently difficult to manipulate ( e.g. in the daily press). At a later point in time, the then current digitally stored log file can be proven to be correct by the published (and therefore known to the general public) hash values, and thus also your own entry from the past, with proof of the existence of the data at a previous point in time is provided.

Example: It should be conclusively recorded that a text already existed today, e.g. to prove the authorship of the text in the future. So you calculate a checksum (for example SHA ) of the text and save this checksum together with the current time stamp in the log file. The operator of such a log file should ensure that the current hash value appears in the daily press at least once a day; you can, however, do this yourself.

The special principle is that the perpetual log file links the hash value of the new log entry with the hash value of the log file itself, so that it is not possible to delete individual entries from the log file without changing the hash value of the log file. A manipulation attempt can thereby be discovered.

example

The principle can be illustrated with an example:

• any entry ( ) in the log file is e.g. B. "Peter Müller owes Hans Huber 10,000 EUR" and has the hash value . ${\displaystyle m}$ ${\displaystyle H(m)}$
• the current -th entry reads "Today the sun is shining" and has the hash value , which is calculated from the hash value and from the current entry "Today the sun is shining". ${\displaystyle n}$ ${\displaystyle H(n)}$ ${\displaystyle H(n-1)}$
• since the hash value is in turn calculated recursively from all previous hash values ​​(together with the respective content), the hash value of the entry is also included in the current hash value. ${\displaystyle H(n-1)}$ ${\displaystyle m}$
• Whenever a hash value changes (i.e. a new entry has been added), the current hash value is published in a daily newspaper or the like. ${\displaystyle H(x)}$
• if an attacker wanted to falsify the log file and insert the amount "100,000" in the entry instead of the amount "10,000", this would change the current hash value of the log file , which can be easily discovered by comparing it with the previously published hash values . ${\displaystyle m}$ ${\displaystyle H(n')}$ ${\displaystyle H(m),H(m+1),...,H(n-1),H(n)}$

In particular, when the hash values ​​of perpetual log files are mutually linked (i.e. the current hash value of log file A is regularly entered in log files B and C and vice versa), manipulation of the entries is practically no longer possible.

application

One of the most prominent applications of the perpetual log files are blockchains , which are the basis for crypto currencies such as B. Bitcoin , Ethereum etc. form.

Web links

• Eternal log file from Lutz Donnerhacke (with detailed background information)
• The never-ending log file ( memento from July 19, 2009 in the Internet Archive ) by Bodo Thiesen ( alpha version , but working).