Algorand, MIT Bitcoin Expo ‘18

Talk given by Professor Silvio Micali

Professor Silvio Micali spoke at the 2018 MIT Bitcoin Expo about his revolutionary consensus algorithm: Algorand. What follows below is a summary of that talk, starting with a competitor: Bitcoin.

Bitcoin Summary

Main idea: Consensus via PoW // Main Assumption: Honest majority of mining computing power


Algorand is effortless and blocks are One-By-One. No Forks and No PoW

Byzantine Agreement — Communication Protocol that when the majority of players are honest, guarantees

  • Agreement — Start: people have values in their head → End: Will agree on same value
  • Consistency — Start: people have one value in their head → End: Will agree on the one value

*Both properties are important

Challenges: slow and players are fixed and known in advance

Algorand Summary

Main Idea: Message-passing Byzantine Agreement // Main Assumption: Honest majority of Money

Main Technical Advantages

More on Security → Adversary can…

  • Immediately corrupt any player he wants, but n/3 overall
  • Totally controls and perfectly coordinates all bad players
  • Attack the protocol
  • Attack the communication NETWORK on which protocol runs
  • Can’t forge signatures

Algorand’s Structure — 2 phases

To start: Algorand is able to support billions of users(it scales). There are good guys and bad actors, but majority are honest

Magic Phase 1: one user is randomly selected → his/her public key becomes common knowledge to the entire network

  • User A makes a new block → looks at all the values/transactions in a blockchain, brings them all together in one block and propagates the block

Magic Phase 2: 1000 people are randomly chosen and they form a committee

  • They agree on the block proposed by User A

Key → If 10% of the committee are bad actors and are dishonest → they don’t agree that the block^ wasn’t made by User A. *Extremely low probability that bad actors are the majority and disagree that User A made the block.

  • Majority are honest and will agree that User A made the block^
  • If you see a block and you weren’t User A or a part of the committee, then you still know that majority chose that block

TL;DR. 2 phases. Phase 1—one person is randomly chosen to make a block. Phase 2 — 1000 people are randomly chosen to approve a block

Common Q & A

Q: Who selects the committee? A: Each committee member secretly selects himself

A: Can bad actors choose themselves…those who choose themselves will have to run his/her own lottery, in which he cannot cheat, but can prove he won! If he wins, then propagates his winning proof and plays the Byzantine Agreement (BA) protocol (thousandth of a second). The probability of winning the lottery is proportional to the total amount of money you have relative to the total amount of money in the network

If there is a Sybil Attack → when user clones himself/herself and attacks the network in large → Algorand ensures that if you have 1mil algos in one key or 1mil keys with one also each → probability is the same

Q: Aren’t Byzantine Agreement (BA) very slow? A: New Super (BA)

A: Expected Handful of Steps. Single and short messages per step!

Q: Can’t the Adversary (Dragon) corrupt the all the committee members after the first step??? A: Separate committee for each Step x!

A: Adversary can’t corrupt the first message sent bc adversary doesn’t know who to corrupt. A committee member speaks once: his winning proof + his step-x message. Nonsense! Player Replaceability → Brand New Property!

Committee members are replaced → Player Replaceability → the block is saved and propagated to the network

Committee Members have no relation to each other bc they are RANDOMLY SELECTED — > TRULY DISTRIBUTED

  • Shared environment allows committee to act as one
In Sum Algorand has — No Forks, No Miners, No PoW, No Wait to Confirmation, Trivial Computation, Perfect Scalability, Transaction Finality, Great Security

In Addition — Security without arbitrary partitions, Flexible Governance without hard forks, Secure Incentives, Deep Roadmap

Julian Bridge in Southern France
Blockchains properly constructed will be as useful an any physical infrastructure ever built. And as beautiful as any infrastructure ever built.
Let’s build it properly!

To learn more, check out our video from the MIT Bitcoin Expo,

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