STARKs vs. SNARKs and the Quantum Threat Famously, STARKs are post-quantum secure but SNARKs break by quantum computers. Why? I'm referring here to the elliptic curve SNARKs, the kinds most of you are familiar with (like Groth16). A SNARK uses a "proving key" secret to allow the prover to answer a certain question. The way the secret is created is by repeating many times a certain math operation. A good analogy is that you start with a Rubik's cube and do a certain operation (say, twisting one side of it + rotating the cube in your hand). Then, you repeat it many times, a million billion gazillion many times. The exact number of times you do that operations -- that's the secret. Then, you present the messed up Rubik's cube for the whole world to view. Now, if you could look at the cube and answer how many times the operation was done to reach this current state, you break the SNARK. One way to do it is take a Rubik's cube and start messing around with it, counting how many times you do the operation till you reach the configuration posted publicly. But that takes a lot of time (a million billion gazillion steps). Aha, but a quantum computer is this really smart computer that can look at the cube and spit out the number: 112,302,305,166 times for example. And with this answer, the SNARK is broken. OK, what about a STARK? In this case, to break a STARK you have to "break a hash". A hash works something like this: You take a Rubik's cube, do one of those operations. Then you write the pattern on a paper, fold it up, cut it up, permute the squares in a crazy way, and post them on a new Rubik's cube. Then you do another operation on the Rubik's cube, and then again move to the paper. And so on and so forth. The important point is this: Rather than doing only one kind of operation (mathematically, a "group operation") in the case of a SNARK, with a STARK you mix a large number of very different operations, that lack connection and structure. And this mixing, of many things, is what confuses computers, both classical and quantum, and saves the day. THE END.