Proof of History (PoH) is a sequence of computations that enables nodes to cryptographically verify the time between two events. This consensus mechanism allows for ‘timestamps’ to be built directly onto the blockchain itself, informing the network that transactions occurred in a particular order without the need for confirmation from other nodes. This reduces the processing weight of the blockchain, making it faster and more energy efficient than many other consensus mechanisms.
PoH relies on a fairly new cryptographic concept — Verifiable Delay Functions (VDFs), which require the running of a specific number of sequential steps to ease the process of verification. Popularised by Solana, PoH is comparatively more efficient than many other algorithms, as a VDF can be solved with just one CPU core. Because no parallel processing is permitted, determining how long each step takes becomes simple.
Additionally, PoH eliminates the time barrier and greatly reduces the processing weight of the blockchain. In the case of Solana, PoH is combined with Tower Byzantine Fault Tolerance (Tower BFT) — Solana’s custom implementation of practical Byzantine Fault Tolerance (BFT) — to ensure a much quicker transaction speed.
