Trust enhancement by multiple random beacons

Random beacons-information sources that broadcast a stream of random digits unknown by anyone beforehand-are useful for various cryptographic purposes. But such beacons can be easily and undetectably sabotaged, so that their output is known beforehand by a dishonest party, who can use this information to defeat the cryptographic protocols supposedly protected by the beacon. We explore a strategy to reduce this hazard by combining the outputs from several noninteracting (eg spacelike-separated) beacons by XORing them together to produce a single digit stream which is more trustworthy than any individual beacon, being random and unpredictable if at least one of the contributing beacons is honest. If the contributing beacons are not spacelike separated, so that a dishonest beacon can overhear and adapt to earlier outputs of other beacons, the beacons' trustworthiness can still be enhanced to a lesser extent by a time sharing strategy. We point out some disadvantages of alternative trust amplification methods based on one-way hash functions

Improvements to time bracketed authentication

We describe a collection of techniques whereby audiovisual or other recordings of significant events can be made in a way that hinders falsification, pre-dating, or post-dating by interested parties, even by the makers and operators of the recording equipment. A central feature of these techniques is the interplay between private information, which by its nature is untrustworthy and susceptible to suppression or manipulation by interested parties, and public information, which is too widely known to be manipulated by anyone. While authenticated recordings may be infeasible to falsify, they can be abused in other ways, such as being used for blackmail or harassment; but susceptibility to these abuses can be reduced by encryption and secret sharing