On Friday, Ethereum co-founder Vitalik Buterin published the third part of his series on cryptographic obfuscation.
He explored a method called "local mixing," which discards lattices and elliptic curves in favor of ideas borrowed from hash function design.
Buterin published the first part on June 29, and the second part, focusing on iO diamond technology, was published on July 28.
In these publications, he discussed constructions involving many lattices. Regarding local mixing, Buterin said it is "a completely different way of doing cryptography." In his post, he wrote that local mixing has no elliptic curves, no prime factorization, and no lattices anywhere in the construction.
According to Buterin, the closest analogue to local mixing is symmetric cryptography, which underlies everyday encryption and hashing.
Garbage Gates and a Backwards-Running Circuit
The local mixing process starts with a circuit consisting of logic gates, such as XOR, AND, and NOT, which passes through a pipeline that ensures the output signal is correct while simultaneously removing any traces of the internal logic.
Buterin wrote that local mixing involves taking the original circuit and adding reversibility, hardening, mechanization, mixing, and finally, obfuscation.
During the mixing process, extra logic gates are scattered into the circuit. The arrangement of elements is then shuffled, and certain small blocks are replaced with other elements that compute the same function.
However, this is not sufficient, which is why the remaining steps are important, as they do most of the work.
Reversibility comes first because it makes everything else possible. Buterin explains that a reversible gate can be rewritten as an arbitrary set of other reversible gates with similar behavior. This is harder to do with an AND or OR gate.
A Bet Based on Past Failures
Buterin still called local mixing a "wild and risky undertaking," writing that it lies in the "graveyard of failed white-box cryptography attempts."
However, he noted that the authors of the local mixing concept argue that more effort and a willingness to accept higher overhead are necessary to prove the viability of this idea.
One proposed way to address the issue is using artificial intelligence, as it could compress three decades of hash function development into a few years. However, it deviates from lattice-based approaches, where the trade-off was based on security assumptions.
Buterin called obfuscation the "final boss of cryptography," and in this latest publication, the "last frontier of cryptography."
He said that the most complex constructions have "literally galactic" runtime, exceeding the lifespan of the universe.
Why Resort to Obfuscation?
A program can be transformed into an encrypted version that still works with ordinary inputs using obfuscation. In this case, ordinary outputs are returned, but the program's code is hidden.
When obfuscation is combined with blockchain, it brings us closer to a "trusted third party that requires no trust," enabling, for example, private, collusion-resistant voting without needing to trust an "N-of-M" committee.
