Proof of History (POH)

What is Proof of History?

Proof of History (PoH) is a sequence of computations that create a verifiable historical record which is used to verify the order of events and the time when transactions occur. This technique establishes the order of events which enables synchronization in the creation of new blocks on the Solana blockchain. Proof of History is a SHA-256 hashing algorithm similar to a Verifiable Delay Function (VDF). It runs continuously, using the output of one iteration as the input for the next.

What is Consensus Mechanism?

A consensus mechanism is a protocol used in blockchain networks to achieve agreement among distributed nodes on the state of the ledger. Its objective is to ensure that all participants in the network agree on the validity of transactions and the sequence in which they are added to the blockchain. Common types of consensus mechanisms include Proof of Work (PoW), Proof of Stake (PoS), and Byzantine Fault Tolerance (BFT).

The Misconception about Solana’s Proof-of-History

Proof of History (PoH) isn’t a consensus mechanism itself, but rather a component of Solana’s consensus algorithm. Think of it like a tool that helps the algorithm work. You could remove PoH and still have a functioning consensus mechanism on Solana. If PoH was the main consensus mechanism, there is no way Solana would continue to function. Solana’s consensus mechanism is called the Tower BFT (Byzantine Fault Tolerance).

While Solana’s consensus mechanism, Tower BFT, can theoretically function without PoH, it would significantly impact its performance and efficiency. PoH is a core component that enables Solana to achieve high throughput and low latency.

How does the Tower BFT work with Proof of History?

Solana’s Tower BFT (Byzantine Fault Tolerance) is a consensus algorithm designed to use the unique capabilities of Proof of History (PoH) to achieve high-performance and scalable consensus in the Solana blockchain network. Tower BFT utilizes the PoH cryptographic clock to provide a reliable and verifiable sequence of events.

While PoH creates a sequence of events that can be used to infer timestamps, Tower BFT primarily uses the order of events established by PoH, rather than the exact timestamps, for organizing and ordering transactions.

How PoH Works with Timestamps

1. Initial State and Hash Function: PoH starts with an initial state and applies a hash function to it. The hash function used is a Verifiable Delay Function (VDF), which requires a certain amount of time to compute.
2. Sequential Hashing: The output of each hash computation is used as the input for the next hash. This process creates a chain of hashes, each representing a point in time.
3. Timestamp Embedding: Each transaction is tagged with a hash from this chain, effectively embedding the transaction within a specific point in time. The hash chain provides a way to prove that the transaction was created after the previous hash and before the next one.
4. Verifiable Sequence: The entire sequence of hashes is verifiable. Anyone can independently verify that a particular transaction occurred at a specific point in time by checking its position in the chain of hashes.

Key Takeaway

In conclusion, Solana’s innovative Proof of History (PoH) mechanism, combined with its Tower BFT consensus mechanism, significantly improves blockchain performance by providing verifiable timestamps and reducing communication overhead. This combination enables high throughput and low latency, making Solana a robust platform for scalable decentralized applications.

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