Lots of good info, I liked how he explained this question:
Forbes: How else does cryptography fit into blockchain technology? How do you use it in Algorand?
Micali: The traditional application of cryptography to blockchain is to prevent an adversary from altering the content of a block or the order of blocks. But in Algorand we use it for doing what we call a cryptographic sortition: we select an unpredictable committee (to add blocks to the network) whose members are not known until they show up with a proof that they belong to the committee. That is really the secret sauce of Algorand, which allows us to be very scalable and very distributed. In some sense, this is a use of cryptography because even though I am running my own lottery (forming the committee members), I cannot cheat. I cannot alter the probability of winning. And if I win, I can prove to you that I’m a legitimate winner of my own lottery.
It is really a new application for cryptography that allows us to unpredictably convene a committee. You cannot somehow control the committee members or know in advance who they are going to be. As you may know, many blockchains propose the blocks by way of a round-robin: participants take turns, and an adversary knows in advance who is going to generate the next block and could perhaps attack. But if the generation of a new block is entrusted to a few committee members, say a few hundred or a thousand, and nobody knows who they are because they are the winners of secret individual lotteries, an adversary cannot go after them in advance. Once these people show up and say, “I won the lottery,” you can believe they are the real winners because nobody can alter the probability of winning or pretend to have won when they have actually lost.