Chaos Factor and Verifiable Random Permutation
In this section we outline the innovative verifiable random permutation
algorithm, which adds additional security protection on top of the
Istanbul BFT consensus mechanism.
Randomness is an important ingredient in designing mechanisms to allocate resources. It is useful for achieving fairness and safety: Everything else being equal, if a resource has to be assigned to a person rather than another person and money cannot be used to compensate, then randomly allocating that resource is fair from an ex-ante point of view [@mamageishvili2020mechanism]. Meaningful use randomness in blockchain design requires trust. One needs to ensure the randomness mechanism cannot be manipulated, but this seems paradoxical given the trustless nature of the decentralized system.
The creation of verifiable identity uncertainty among the validators has always been an integral part of Proof of Stake mechanism design. It is essential for security and decentralization that the next validator is selected in a random yet verifiable way. Many verifiable random functions have been proposed and used specifically for this task. In the ETM chain validation process, the total number of validators is 21 in each round. There are permutations of these nodes. The consensus mechanism will create uncertainty in the ordering of the nodes, by what we call verifiable random permutation. We use information from the last block of the previous round and SHA256 to create a chaos factor. Then, this chaos factor can map into a specific permutation of the 21 nodes, [@SLY]. This creates an ordering of the validators, uniformly distributed among the possible permutations, and helps to mitigate the risk of malicious nodes coalition. The whole process can be verified by any other nodes since the Hash is broadcasted and calculations can be performed very quickly.