Proof-of-History (PoH)

A cryptographic time-stamping mechanism used by the Solana blockchain to sequence events and enable high transaction throughput with verifiable order.

What is Proof-of-History (PoH)?

Proof-of-History (PoH) is a core innovation of the Solana blockchain, introduced by Solana Labs founder Anatoly Yakovenko in 2018. It is not a consensus mechanism but a decentralized clock that cryptographically timestamps transactions to create a verifiable, chronological order of events. By using a verifiable delay function (VDF) based on SHA-256 hashing, PoH allows Solana validators to process transactions without needing to communicate extensively to agree on their order, significantly boosting scalability. This enables Solana to achieve up to 65,000 transactions per second (TPS) with average fees of $0.00025, as reported in 2025 network metrics.

In practice, PoH works by generating a sequence of hashes where each hash depends on the previous one, creating a tamper-proof timeline. Validators can independently verify this sequence, reducing the time and computational overhead compared to traditional blockchains like Bitcoin or Ethereum, where nodes must synchronize to confirm transaction order. PoH complements Solana’s Proof-of-Stake (PoS) consensus, where validators stake SOL to secure the network, allowing Solana to process blocks every 400 milliseconds. As of September 2025, Solana’s PoH has contributed to over 200 billion transactions processed, supporting DeFi platforms like Serum and NFT marketplaces like Magic Eden.

While PoH enhances efficiency, it has faced scrutiny for centralization concerns, as early Solana validators required high-performance hardware, though optimizations have since lowered barriers. Network outages, like the 17-hour downtime in September 2021 caused by a transaction surge, exposed reliance on PoH’s leader schedule, prompting upgrades like QUIC protocol integration. Despite these challenges, PoH remains a cornerstone of Solana’s ability to handle high-throughput applications, such as Visa’s USDC settlement trials in 2023.