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Algorand’s Chief Cryptographer: Verifiable Random Function(VRF) is Key to Solving the Blockchain Trilemma

Algorand, the blockchain protocol founded by Silvio Micali, a Turing Award-winning cryptographer and professor of computer science at MIT, is undoubtedly among the most anticipated blockchain project in 2019.

Sergey Gorbunov, chief cryptographer at Algorand that aims to solve the “blockchain trilemma” suffered by existing mainstream blockchains like Bitcoin and Ethereum, shared his insights into how Verifiable Random Function(VRF) helps solve the bottleneck of blockchain at 8BTC Boost’s recent AMA (“Ask Me Anything”) event, as part of the latest episode of Geekhub Global Online.


Q: What is  Verifiable Random Function(VRF) ? How does it work?

Sergey:  Verifiable Random Function (VRF) is a cryptographic primitive that maps inputs to verifiable pseudorandom outputs. That is, informally, once you fix a key-pair and an input X, a VRF produces a unique pseudorandom verifiable output.

VRFs were introduced by Micali, Rabin, and Vadhan in  1999. Today the primitive is used in various cryptographic schemes, protocols, and systems. (For more technical details about VRF, please refer to this blog .)

Q: How is VRF used in Algorand blockchain ?

Sergey: At the core of the Algorand Blockchain is a fast Byzantine Agreement protocol. However, the agreement is not performed between all users in the network. Instead, it is confined to a small randomly chosen committee of users for each round.

For each block, every user in the Algorand system performs a secret self-selection based on his/her VRF secret key. If the VRF value that the user obtains is less than some threshold, then the user is selected to serve on the committee to perform an agreement for the block.

Q: What are the advantages of adding VRF to the consensus mechanism?

Sergey: Adding VRF to the consensus mechanism allows to scale blockchain systems to support millions or  billions of users. This is because we can randomly sample a small set representing a population to make decisions and run consensus.

Moreover, it allows to support very strong adversary models, where users secretly self-select themselves. No one knows who the selected users are, until they propagate their associated VRF outputs/proof pairs and messages that they wish to sign.

Many PoS blockchains only supports “static or semi-dynamic” committees. Using a VRF, we can efficiently rotate a committee for every block. Any user in the system can participate and  consensus for any block.

Simply put, VRF brings  great scalability and very strong security to  the consensus mechanism.

Q: In the case of multiple candidate blocks, how to quickly reach the consensus within the group? How Algorand specifically deals with this problem?

Sergey: The parameters of the cryptographic sortition mechanism are set to select several candidates (e.g. 20) for every block proposer. In practice, this means that a small number of users, not only one, will have an output to their VRF functions that falls within the “winning” range to be a block proposer. Each candidate then has to propagate their candidate block and “winning ticket” for the round to the network. The candidate with the lowest “winning ticket” is chosen as the block proposer. Therefore if some candidate block proposers are not online, they will not be part of the pool of candidates considered at the end.

Q: How many users are required to sign for a block?

Sergey: For every block, Algorand samples  a random subset of users to run  Byzantine Agreement for that block,  so the number of users that have to sign for the block  is approximately a couple of thousands. In addition,  Algorand can support  thousands of transactions per second.

Q:  What is the current status of Algorand?  What is its goal in 2019?

Sergey: We are currently working on  scaling the test network and improve it for pre- launch.  After we test it  even more with the broader community,we plan to show it to the public.

The initial blockchain will have the basic transactional support and will show to the developers how  they can use the platform to build  interesting applications through APIs, menus  and develop tools.

Algorand does not plan to run an one-time ICO like most other projects do. Instead, we have a continuous series of auctions that will be used to sell  a part of the currency. So most capital from auctions, however, will be used towards different stabilization mechanisms,  building a community and extending the blockchain.


About Alogrand

Founded by cryptography pioneer Silvio Micali, Algorand aims to address the “ blockchain trilemma” with a platform that delivers decentralization, scalability and security. It intends to empower businesses and create a truly decentralized world through its first-of-its-kind, permissionless, pure proof-of-stake protocol. In October 2018, Algoand has raised $62 million in new funding.

About 8BTC Boost’s Geekhub Global Online

Geekhub Global Online,a global blockchain event featuring online courses and dialogues, is developed by 8BTC Boost. The event regularly invite experienced technology companies around the world to deconstruct blockchain technology online to deliver cutting-edge, high-quality blockchain technology content to the Geekhub technology community. Community members can also participate in live interactions to explore the emerging technology.


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