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Byzantine Agreements to the Rescue of Blockchain — Silvio Micali, Algorand

Recap of a talk from Silvio Micali, Co-Inventor of Algorand, at the (Off) The Chain Summit presented by Pillar as part of Boston Blockchain Week.

Silvio Micali, Co-Inventor of Algorand

Silvio Micali is the Co-Inventor of Algorand, a scalable, secure and decentralized digital currency and transactions platform. Micali is an MIT Professor of Computer Science and Electrical Engineering. Micali is also the co-inventor of zero-knowledge proofs, and has received many accolades for his work in the computer science field, as a recipient of the Turing Award (in computer science), of the Goedel Prize (in theoretical computer science) and the RSA prize (in cryptography). He is well known for his work in cryptography, zero knowledge, and protocols.

Micali recently joined us at the (Off) The Chain Summit presented by Pillar to explain how he believes byzantine agreements will come to the rescue of blockchains.

Micali began his talk with a basic explanation of Algorand’s core principles:

  1. No forks, no miners, no proof of work
  2. Perfect scalability, transaction finality
  3. Great security

So how is Algorand approaching solving the blockchain trilemma of decentralization, scalability and security?

“Magic,” jokes Micali.

Algorand operates on pure proof of stake. To fully understand the principles of pure proof of stake, it is first important to understand what it is not.

Proof of stake is not delegated proof of stake. Delegated proof of stake is when a certain number of people, say 20 people, are selected to represent the network. Those 20 people are responsible for generating the additional blocks for the month. Micali believes this is, quite simply, a bad idea.

“Those 20 people will have a target on their chest saying shoot me, shoot me!” Micali explains. If the network has knowledge of these 20 influencers, it is easy for a bad actor to launch a denial of service attack against one of them, taking out the whole system.

It is also not bonded proof of stake. In bonded proof of stake, a select number of people will push money into the middle of a table — it could be two people, could be 200 people, and their influence over the next block will be proportional to the amount of money they have pushed into the middle of the table.

Bonded proof of stake, Micali believes, is a hidden form of centralization. Not everyone can afford to push a large percentage of the disposable income into the middle of the table where they cannot access it. “We are rolling out a red carpet for big thieves with deep pockets to put in the middle of the table a disproportionate amount of money for the only reason to control the blockchain,” Micali explains.

Algorand avoids these two forms of hidden centralization by implementing pure proof of stake. Pure proof of stake operates on three main ideas:

  1. No punishment needed: The system is designed so that cheating should be impossible, making punishment for bad actors unnecessary.
  2. Money always at your fingertips: Your money is not pushed into the middle of the table where you can’t access it — decisions are made based off of the total amount of money you have in the network.
  3. Security: If the majority of the money in the system is in the hands of good actors, the blockchain will be secure.

Acting on the values of pure proof of stake, Algorand operates in two phases to achieve their core principles of scalability, security, and true decentralization.


While randomly selected, the committee of 1,000 users volunteers to have themselves selected. Each user who wishes to participate in the committee runs their own cryptographically fair lottery on their computer. The computer then tells the user if they are approved or not within a microsecond. Every user who wishes to be a part of the committee is told at the same time — within that same microsecond. This is a large part of what Micali believes makes the system more scalable than other solutions out there. Not only is it fast, but “nobody has to talk to anybody else,” adds Micali.

In the instance that a user is approved to be part of the selection committee, the user will be given a “winning ticket”. The user can then use this ticket to prove they are part of the committee and hand it in with their vote either for or against the next block.


“This is the ultimate security,” asserts Micali. In order to corrupt a powerful user, a bad actor would need to have knowledge about who was on the committee. With Algorand, only until the block is propagated does the network become aware of who made the vote.

“I am assuming I am a bad and powerful adversary, I have the power to corrupt anybody,” explains Micali. “But I have a problem — whom should I corrupt? I look at the billion users and I try to see who is on the committee, but I don’t know. So I don’t know whom I should corrupt.”

Only until after the vote is cast and the block is propagated throughout the network is the identity of the committee revealed, but by then, it is too late to make any meaningful attacks.

True Decentralization

A new and super fast byzantine agreement allows Algorand users to agree on the new block while the block is propagated around the network. “I prefer byzantine agreements [to other methods of agreeing on blocks],” explains Micali. “Once you have an approach which is proposed and agreed, and it is very fast to agree, you can use it to of course agree on the next block, but you can use it to agree on almost anything, such as monetary policy.”

This not only gets rid of the need for forks, but also allows for true self governance and decentralization.

“I believe in governance, but I believe in a distributed world. So I believe in self governance, but self governance needs a technical tool,” Micali asserts. With Algorand, the byzantine agreement intrinsic to the protocol creates a very strong and mathematically certain agreement, letting users know where the network stands on an issue at any point in time.

As many blockchain practitioners have agreed, blockchain is still in the architecture building phase. Micali likens building Algorand to the great Julian bridge. “Architectures have great beauty and lasting power,” Micali concludes, “Let’s build it right and lets build it together.”

Written by: Katie Mulligan



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