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

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

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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!

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To learn more, check out our video from the MIT Bitcoin Expo '18

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