Proof-of-Elapsed-Time
Proof-of-elapsed-time is a lottery protocol that uses trusted execution environments (TEEs) to ensure safety and randomness of the leader election process. TEEs are provided by special security-hardened Intel hardware (SGX, Secure Guard Extensions). The approach is based on a guaranteed wait time provided through the TEE; every validator requests a wait time from a trusted function, and the validator with the shortest wait time for a transaction block is elected leader. This randomly distributes leadership election across the entire population of validator. The probability of election is proportional to the resources contributed (in this case, resources are general purpose processors with a trusted execution environment).
Strengths - Proof-of-elapsed-time is suited to consumer markets requiring high aggregate throughput across many participants, but where short-term finality is less important. Does not require as much electricity as Proof-of-work, which makes mining cheaper. The low cost of participation increases the likelihood that the population of validators will be large, increasing the robustness of the consensus algorithm. Weaknesses - Requires Intel hardware.
Proof-of-replication
Is a Proof-of-space, but additionally ensures that unique physical storage is dedicated to storing the data. The prover cannot pretend to store the data twice and deduplicate the storage.
Proof-of-retrievability
Is a Proof-of-space. Requires a node to also demonstrate the original data can be reconstructed eventually from the proofs.
Proof-of-secure-erasure
Is a Proof-of-space. Requires a node to verify that it has just erased (overwritten) all its writable memory.
Proof-of-spacetime
Is a Proof-of-space. Requires a node to prove it has as spent some ‘spacetime’ (storage space used over time) resources. This is Proof-of-space with a sequence of checks over time.