The core mechanism of Proof of History. A SHA-256 hash is computed sequentially—each hash takes the previous hash as input—creating an ordered, unforgeable timestamp sequence. The PoH generator runs approximately 400,000 hashes per slot. Data (transactions) can be inserted into the chain by mixing their hash with the current state.
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The core mechanism of Proof of History. A SHA-256 hash is computed sequentially—each hash takes the previous hash as input—creating an ordered, unforgeable timestamp sequence. The PoH generator runs approximately 400,000 hashes per slot. Data (transactions) can be inserted into the chain by mixing their hash with the current state.
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Consensus, leader rotation, slots, epochs, and the runtime.
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SHA-256 Hash Chain (sha256-hash-chain) Category: Core Protocol Definition: The core mechanism of Proof of History. A SHA-256 hash is computed sequentially—each hash takes the previous hash as input—creating an ordered, unforgeable timestamp sequence. The PoH generator runs approximately 400,000 hashes per slot. Data (transactions) can be inserted into the chain by mixing their hash with the current state. Related: Proof of History (PoH), VDF (Verifiable Delay Function), Tick
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A clock mechanism that cryptographically proves the passage of time between events. PoH uses a sequential SHA-256 hash chain where each output becomes the next input, creating a verifiable ordering of events without requiring consensus. The leader produces ~400,000 hashes per slot (~400ms), and any validator can verify the sequence in parallel, enabling Solana's high throughput by removing the need for validators to agree on time.
Verifiable Delay Function—a function that takes a prescribed amount of sequential computation to evaluate but whose output can be quickly verified. Solana's Proof of History uses a SHA-256 hash chain as a practical VDF: computing the chain is inherently sequential, but verifying any segment can be parallelized across multiple cores.
A PoH entry with zero transactions that advances the clock. There are 64 ticks per slot by default, each representing a fixed number of SHA-256 hash iterations. Ticks establish the passage of time even when no transactions are being processed, maintaining the PoH chain continuity.
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A clock mechanism that cryptographically proves the passage of time between events. PoH uses a sequential SHA-256 hash chain where each output becomes the next input, creating a verifiable ordering of events without requiring consensus. The leader produces ~400,000 hashes per slot (~400ms), and any validator can verify the sequence in parallel, enabling Solana's high throughput by removing the need for validators to agree on time.
Verifiable Delay Function—a function that takes a prescribed amount of sequential computation to evaluate but whose output can be quickly verified. Solana's Proof of History uses a SHA-256 hash chain as a practical VDF: computing the chain is inherently sequential, but verifying any segment can be parallelized across multiple cores.
A PoH entry with zero transactions that advances the clock. There are 64 ticks per slot by default, each representing a fixed number of SHA-256 hash iterations. Ticks establish the passage of time even when no transactions are being processed, maintaining the PoH chain continuity.
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A clock mechanism that cryptographically proves the passage of time between events. PoH uses a sequential SHA-256 hash chain where each output becomes the next input, creating a verifiable ordering of events without requiring consensus. The leader produces ~400,000 hashes per slot (~400ms), and any validator can verify the sequence in parallel, enabling Solana's high throughput by removing the need for validators to agree on time.
Solana's custom BFT consensus algorithm built on top of Proof of History. Tower BFT uses PoH as a clock to reduce communication overhead in traditional PBFT from O(n²) to O(n). Validators vote on forks with exponentially increasing lockout periods—each consecutive vote doubles the lockout, making rollbacks progressively more expensive. A fork is finalized when it reaches supermajority (66.7%+ of stake).
A time window during which a designated leader validator can produce a block. Each slot lasts approximately 400 milliseconds. Slots are numbered sequentially from genesis and grouped into epochs of 432,000 slots (~2-3 days). Not every slot produces a block—a skipped slot means the leader was offline or too slow.
A set of entries produced by a leader during a single slot. A block contains transactions bundled into entries, each with a PoH hash proving ordering. Blocks are broken into shreds for network propagation via Turbine. Maximum block size is limited by compute units (48M CU cap per block) rather than byte size.