Randomness is the cornerstone upon which cryptographic standards are built. It is used to generate the keys and seeds used in cryptographic schemes. The challenge related to the generation of randomness is the generation of truly random data. Current techniques rely on deterministic approaches – hardware utilizing classical physics, and any available inputs that might add some level of unpredictability – which leads to the generation of pseudo-random data in the vast majority of the cases. Failure to ensure sufficient randomness in cryptographic processes can lead to real-world attacks on otherwise secure systems. This even extends to quantum random number generators which is why there is a need to develop schemes for true randomness.

Conversely, quantum generation of randomness harnesses the power of the non-deterministic nature of quantum mechanics. Generating quantum random numbers can be built in many ways, as has been illustrated by the various approaches used to date, including beam splitters with detectors, vacuum fluctuations in coherent light, and squeezed coherent light mechanisms, among others. Despite the fact that these methods are non-deterministic, they lack the ability for an end user to guarantee that the device is working correctly. This ability in a device (sometimes known as device independence or more commonly, as certifiably quantum generation) is at the heart of the qRNG, Ironbridge, used in our solution.

Ironbridge generates randomness through a quantum process evaluated as quantum verifiable which utilizes a test for the violation of a Bell Inequality, or a higher order test of a Mermin Inequality on a NISQ machine. Such a violation, along with various other security tests, are taken as mathematical proof that the output could have only come from a quantum source and is non-deterministic and thus maximally random for a physical system. For the experiments in this paper, a quantum computer was used to generate the entropy. 

Given the distributed nature of a blockchain, ideally each entity running a node should have its own local source of quantum entropy: a qRNG device. However, it was not feasible to provide each node with its own qRNG for our pilot, so we used a central source of quantum entropy. As discussed throughout this paper, current cryptographic schemes used in SSL/TLS are not quantum-safe, so using them to distribute the entropy would have broken the quantum-safeness at the start.

We decided instead to design a protocol that allowed nodes to create a quantum safe tunnel between themselves and the entropy distribution point to ensure that this communication could be considered quantum safe. In order to do this, the entropy source creates a first key, splits it into several parts, and delivers it to the node through various TLS channels. Nodes have a time out to receive the key, recompose it, and use it to authenticate against the entropy source.