Proof of History (PoH)

    Pathik Bhattacharya
    Pathik Bhattacharya
    Published on November 20, 2022 2:08 PM

    Updated on January 10, 2023 1:03 PM

    As the name indicates, Proof of History (PoH) provides proof of historical events. Solana's PoH technology allows "timestamps" to be directly recorded into the blockchain.
    Proof of History (PoH)
    Source: unsplash

    To secure a transaction, Blockchain technology employs various consensus mechanisms. The proof that a transaction has happened or not is confirmed by the consensus mechanisms. Proof of work was one of the first consensus methods used in mainstream cryptography. But as time evolved so did the method of confirming transactions on the blockchain ledger. As PoW had a lot of drawbacks (mainly related to power consumption) many consensus mechanisms were developed, and one of the methods is Proof of History.

    Instead of relying on the transaction's timestamp, you could demonstrate that the transaction occurred before and after an event. The Proof of History is a Verifiable Delay Function with a high frequency. A Verifiable Delay Function needs a certain number of sequential steps to assess, but it yields a unique result that can be easily and publically validated.

    What is Proof of History?

    Proof of History (PoH) is a method for adding time to the blockchain to lessen the burden on network nodes when processing blocks. In a classic blockchain, reaching an agreement on when a block was mined is equally as crucial as reaching an agreement on the transactions in that block. It is critical because timestamping notifies the network (and any observer) that transactions occurred in a specified sequence.

    Proof of History is a computation sequence that may be used to cryptographically prove the passage of time between two occurrences. It employs a cryptographically safe function that is built in such a way that the output cannot be anticipated from the input and must be entirely performed to produce the output. 

    The function is executed in sequence on a single core, with the previous output serving as the current input and a periodic record of the current output and the number of times it has been called. External computers can then recompute and verify the result in parallel by examining each sequence segment on a different core. Data can be timestamped into this sequence by attaching it (or a hash of some data) to the function's state. 

    The recording of the state, index, and data as they were appended to the sequences offers a timestamp that can ensure that the data was created before the next hash in the series was constructed.

    How Does it Work?

    This technique of timestamping is made possible by an SHA-256, sequential-hashing verified delay function (VDF). It works by taking the outcome of a transaction and using it as the input for the next hash, allowing everyone to see which event occurred in a certain sequence. PoH significantly minimizes the processing weight of the blockchain, making it faster and more energy-efficient than many of his peers because the VDFs can only be solved by a single CPU score.

    Source: Infoworld

    PoH has yet to be evaluated on a broad scale because it is only used by Solana.


    When you take a photograph of a newspaper, you are establishing proof that your image was taken after the newspaper was published, or that you have some control over what the News publications publish. You may use Proof of History to construct a historical record that demonstrates an event that occurred at a given point in time.

    Significance of Proof of History

    The Proof of History concept gives a solution to cryptographically show the passage of time and where events occur in that timeline. This consensus technique is used in conjunction with a more traditional algorithm such as Proof of Work (PoW) or Proof of Stake (PoS). In Solana, the Proof of History makes the Proof of Stake more efficient and robust.

    PoH enables network fault tolerance by offering a robust method for eventual consistency, even in the face of a huge network split (or fork). Because nodes can rely on the system structure to ensure transaction sequencing, they may dedicate more resources to quickly processing blocks and entering valid blocks into the ledger.

    Protocols Using Proof of History

    Solana's Proof of Stake (PoS)-based consensus mechanism, Tower BFT, employs the network's Proof of History (PoH) approach as a reminder before consensus to reduce communication costs and latency.

    Each time a validator votes on a fork, it is limited to a set number of hashes called a slot. The present network setup takes roughly 400 milliseconds for one slot (ms). Every 400ms, the network has a possible rollback point, but each subsequent vote increases the amount of time it must wait until it may unroll that vote. To summarize, secondary votes make it far more difficult to reverse transactions in a certain slot.

    As a result, a block with a large number of votes has a stronger chance of remaining in the chain permanently.

    Source: LeewayHertz

    Note: Solana is the only known protocol that uses Proof of History consensus.

    Pros of Using PoH

    Low transaction prices: Solana has lower transaction fees than competing networks like as Ethereum. As a result, Solana is a great option for frequent transactions and money transfers.

    Scalability: Transactions on the Solana network are extremely fast. As a result, the whole picture becomes more scalable.

    Cons of Using PoH

    Solana currently utilizes less than 1,200 validators to validate network transactions.

    Solana is frequently described as an Ethereum killer, however, the network has fewer dApps in comparison. On Solana, around 350 dApps have been created, but on Ethereum, over 3,000 dApps have been created.

    Proof of History is riddled with problems. For example, because this strategy has never been tested on a large scale, we don't know if it works properly. Furthermore, several weaknesses and attacks in Solana have already been uncovered, some of which were triggered in part by Proof of History. As a result, we are unsure if Proof of History is a secure consensus mechanism.


    The Proof-of-History consensus has tremendous potential. Most consensus procedures are slower and use more energy than Proof-of-History. This is due to the timestamps assigned to each transaction.

    Proof-of-History has a bright future ahead of it as the ecosystem attracts more and more developers. And it is absolutely worthwhile to monitor the protocol's project as it develops.