  We propose a new unconditionally secure bit commitment scheme based on
Minkowski causality and the properties of quantum information. The receiving
party sends a number of randomly chosen BB84 qubits to the committer at a given
point in space-time. The committer carries out measurements in one of the two
BB84 bases, depending on the committed bit value, and transmits the outcomes
securely at light speed in opposite directions to remote agents. These agents
unveil the bit by returning the outcomes to adjacent agents of the receiver.
The security proofs rely only on simple properties of quantum information and
the impossibility of superluminal signalling.
