Proof of Elapsed Time (PoET)

Proof of Elapsed Time (PoET) was invented in 2016 by Intel. It is used to solve the ‘Random Leader Election’ problem and is more helpful in permissioned BC. PoET reaches consensus by implying a random timer at every node in the network. The random timer decides which node gets to validate the block on BC and gets rewarded. PoET focuses on efficiency and ensures there is an equal probability of every node to become the miner and validate the block. The working of PoET is divided into the following two stages:

1. Verification and Joining Phase: PoET uses a sophisticated technology called Soft- ware Guard Extension (SGX) which is a security-related instruction code to be executed on a central processing unit that isolates certain trusted regions of data and code. SGX enables a trusted execution environment (TEE) [50] that allows only trusted code and data to be executed on the system applications. A node wanting to join a permissioned network needs to be trusted. The node needs first to download the PoET code and run on SGX. SGX renders an attestation and a new private/public key pair. The node signs the attestation and forwards this signed attestation (with the public key generated) with a request message to join the network. The already verified nodes in the network verify the attestation. The network can either accept or reject the attestation based on the verification. If accepted, the node is allowed to be part of the BC network.

2. Mining lottery based on random timer: For the mining process to start, a node needs to be elected for validating a block. Each trusted node receives a timer object from the trusted code using SGX. The timer is entirely randomized and prevents malicious users from fooling the network by continuously acquiring the shortest timer. All the nodes go into a waiting state when their timer starts and the node whose timer expires first gets a chance to validate the block and get the reward. This leader election is broadcasted to the entire network to announce the winner node waited for a specific amount of time before the mining process started. Once the transactions are validated and the block is mined, the random timer starts again to choose the next node to participate in the mining process.

Applications like Hyperledger Sawtooth developed by Intel Corporation work on the concept of PoET. The randomized timer used in PoET makes it more efficient and eliminates the need for any compute-intensive mining process. The randomized timer enables an equal probability of all the trusted nodes to get a chance to mine the block and claim the reward. Also, PoET does not suffer from any scalability issues. PoET has a dependency on TEE for establishing the trust to take part in the network. Also, it is susceptible to a Sybil attack where the attacker creates a lot of fake identities and tries to influence the network.