<aside> 💡 See https://github.com/subspace/protocol-specs/blob/main/docs/consensus/proof_of_time.md for the latest version

</aside>

• Contents

Terminology

Timekeeper

Timekeepers are the nodes that run the evaluation of the Proof-of-Time chain and gossip their outputs to other nodes. Timekeepers are expected to dedicate a full CPU core to Proof-of-Time.

Node

A Node or Consensus Node (unless otherwise noted as Timekeeper) is a PoT client node that does not run the PoT evaluation component. It only consumes PoT messages from Timekeepers or the blockchain.

Primitives

We construct a PoT function by iterating AES-128 a large number of times. The prover evaluation latency for the fastest available hardware platform is calculated as the number of iterations times the latency for a single iteration of AES-128 on that hardware platform. We may then tune the number of iterations based on the lowest-latency hardware platform at the time to guarantee the minimum wall-clock time required for anyone to evaluate the PoT.

Public Constants

• BLOCK_AUTHORING_DELAY: number of slots between when the new global randomness value is revealed at slot t and when the farmer can claim block with that randomness at slot t + BLOCK_AUTHORING_DELAY, currently set to the maximum time needed to produce a PoS solution (4 slots, ~4 seconds)
• POT_ENTROPY_INJECTION_INTERVAL: number of blocks after which the proof-of-time chain input is updated with consensus chain entropy, currently 50 blocks, roughly equal to ~5 minutes at the expected block production rate
  • Note
• POT_ENTROPY_INJECTION_LOOKBACK_DEPTH: depth at which the injected block is taken, measured in multiples of POT_ENTROPY_INJECTION_INTERVALs, currently 2 (equal to 100 blocks, the archiving depth)
• POT_ENTROPY_INJECTION_DELAY: number of slots between when the injection condition is met at slot t and when the injection into the PoT chain happens at slot t + POT_ENTROPY_INJECTION_DELAY, currently equal to 15 slots
• NUM_CHECKPOINTS: number of checkpoint values for the proof-of-time verification published in 1 slot, currently 8
• EXPECTED_POT_VERIFICATION_SPEEDUP: expected speed-up of PoT verification to evaluation, currently 7. Used by nodes to decide whether to attempt to verify or evaluate locally under a potential DoS attack.

Parameters

• pot_slot_iterations: number of iterations of PoT function required per single time slot. Should be divisible by 2 * NUM_CHECKPOINTS

APIs