Cryptography and blockchain technology have seen a significant uptick in global interest since the inception of Bitcoin in 2008. We have since experienced first-hand the birth of many new projects, each using a different twist in their underlying consensus mechanism in order to find the perfect fit for a globally distributed blockchain network. Some of these new projects focused mostly on trying to fix the inefficiencies plaguing existing blockchains by coming up with innovative ways to achieve consensus.

The following paper will give a brief overview of the most popular consensus mechanisms currently used by blockchain projects. It will also cover their main strengths and weaknesses, as well as their position in the scalability trilemma[1] (scalability-security-decentralization).

 

Proof of Work (PoW)

A proof of work protocol is a system or a function that requires a significant amount of processing power to solve, but once solved, can be very easily proved. In 2009, Bitcoin became the first mainstream application of its utility. Its core comes from the use of hash functions, a function called SHA-256 that takes an input and converts it to an alphanumeric string. The idea is that the same input will always produce the same hash output, but the slightest change in the input will completely shuffle the hash output.

Consensus Mechanism 1

Since a given set of data can only generate one hash output, the ‘proof’ that is required from PoW is to find which integer (called a nonce) added to the initial public data will give a hash output starting with a specific set of numbers (ie: twenty 0s). The people looking for the nonce that satisfies these specifics (the miners), all compete against each other because the first miner to solve it gets a monetary reward. The winner broadcasts his nonce, which everyone can instantly verify, and if proven right, the block is effectively mined and added to the blockchain.

The intense computation, the work that is needed to find the right nonce is expensive since it requires a lot of electricity and is the reason why the miner is rewarded for adding to the blockchain.

ASIC optimized (Bitcoin)

An Application-Specific Integrated Circuit (ASIC) is an integrated circuit customized for a particular use, rather than intended for general-purpose use. ASIC optimization refers to hardwares specifically made to significantly improve the capacities of regular PoW miners. It optimizes Bitcoin mining operations by reducing the space utilized and power consumed by Bitcoin mining hardware.

ASIC resistant (Ethereum, Monero)

When an altcoin is said to be ASIC resistant, it refers to the way traditional PoW miners solve their functions. A very powerful computer normally has a better chance of finding the right nonce than a slow one, because it can run more operations in the same amount of time. The difference with ASIC resistant coins is that they do not require more ‘software power’ to achieve a better performance, but more memory which translates to more physical hardware needed. The idea is to decentralise the mining power that is shared between a few mining pools.

Braided PoW (Kadena)

A braided Proof of Work is a unique consensus method used by Kadena in their Chainweb protocol. It is a network that represents a blockchain of blockchains. Their parallel-chain architecture can combine hundreds to thousands of Proof-of-Work blockchains. The individual chains incorporate the Merkle roots (a special hash that is included in the header, or summary of each block, used to quickly verify the validity of a block) of each other to enforce a single super chain.

For the braided PoW to be valid, each chain must, in addition to validating transactions in its own chain, validate block headers of some number of pre-specified chains in order to produce a new block. The more blockchains that are part of the protocol, the less feasible it is to attack the network.

Consensus Mechanism 2

Scalability trilemma

PoW is an extremely decentralized method due to the fact that literally anyone with a computer and an Internet connection can begin validating transactions and mining. The intense calculation needed to solve a PoW nonce is its own security system making it impractical to attack due to the incredible amount of computational power that it would require. On the other hand, it is relatively easy to attack chains with low hashing power since the hardware can be used for multiple chains. This means that a malicious user can destroy a small chain without losing their hardware[2]. Also, PoW is not scalable, as it takes longer to validate due to the heavy work and the slow transaction per second output. Kadena is an exception to this because its network of blockchains can theoretically process an increasing number of transactions as the network grows.

Projects

Proof of Work is used by a variety of blockchains including Bitcoin, Litecoin, ZCash and many more. It is the most commonly used consensus mechanism.

Pros: It is secure, robust and has been tested extensively.

Cons: The mining equipment is expensive to acquire and to use; thus, creating an oligopoly for the ones that can afford it. It’s also way slower and usually more expensive because miners have to recoup their electricity costs + amortize their hardware.

 

Proof of Stake (PoS)

Proof of Stake is a consensus method derived from Proof of Work. It states that a person can mine or validate block transactions according to how many coins he holds. This means that the more coins owned by a miner (the bigger his stake), the more “mining power” she has[3]. This way, instead of relying on hardware and expensive calculations, the deciding factor is how involved one is in the blockchain. By locking some coins as a “stake”, it gives to the validator (the Proof of Stake equivalent of a miner) a chance to be picked to create the block. The probability to be picked is proportional to his stake percentage out of all the available coins that were stacked. PoS was created as an answer to the overwhelming electrical resources needed to complete a Proof of Work.

Casper (Ethereum 2.0)

Casper the Friendly Ghost is the PoS protocol that was to be used by Ethereum. It’s a hybrid of PoW and PoS and its model is used to give finality (concept where a block is considered ‘final’ instead of ‘old enough to probably be valid’ like in the PoW consensus) to blocks. It differs from the regular Proof of Stake because it penalises malicious actors with what is called ‘slashing’ where block validators who validate false data or contradicting data get their deposit destroyed. Casper is a layer on top the Ethereum blockchain. Ethereum is now working on an updated version of Casper (Shasper) that will include sharding. In this protocol, there is a central PoS chain which stores and manages the current set of active PoS validators. Every shard (e.g. there might be 1024 shards in total) is itself a PoS chain, and the shard chains are where the transactions and accounts will be stored.[4]

One of Casper’s features is Casper the Friendly Finality Gadget (Casper FFG). Its design is a PoS protocol overlaying on top of a PoW protocol. So while blocks are still going to be mined via PoW, every 50th block (initially 100) is going to be a POS checkpoint where finality is assessed by a network of validators.

Hybrid PoW/PoS (Decred)

The Decred system uses both PoW miners and PoS voters for its consensus mechanism. Miners create a block in the traditional way, and shortly after shareholders vote to prove that the block is valid. The voters purchase units of votes, temporarily looking their tokens in the network, and 5 voters are picked at random where the majority becomes the consensus. If the vote is favorable, the block is validated and miners & voters get rewards. If not, the block is discarded and only the voters get the reward.

Ouroboros (Cardano)

Cardano’s Ouroboros is the first implementation of a Proof of Stake protocol and is very close to the traditional known PoS. The difference is that they separate physical time into blocks to which are assigned the validators, called slot leaders. A slot has a leader that is picked at random based on the amount of stake that he has, and a group of slots is called an epoch. There is only one epoch working at a time, meaning that if there is 10 slot leaders, there is at most 10 blocks created at a time during an epoch. It takes around 15 slots to validate a transaction, this currently being within 5 minutes. The network is also expected to have a 50% byzantine resistance.

Honeybadger PoS (Polkadot)

The Honeybadger BFT protocol is an asynchronous BFT protocol, which guarantees liveness without making any timing assumptions. By favoring throughput over latency, they are marketing themselves for blockchains who do not need their output instantaneously (ie: Visa needing an average of 2,000 transactions/second). They completely remove the time factor in their consensus method because most BFT systems assume a weak synchrony, where data will be delivered at some point, but it is unknown when.

Their design is optimized for a cryptocurrency-like deployment scenario where network bandwidth is the scarce resource, but computation is relatively ample. This allows them to take advantage of cryptographic building blocks (in particular, threshold public-key encryption) that would be considered too expensive in a classical fault-tolerant database setting where the primary goal is to minimize response time even under disagreement. They are selecting a random committee to perform BFT in every different epoch.

Scalability trilemma

Similarly to PoW, PoS is very decentralized since anyone can stake tokens and start participating in the consensus and governance of their chosen blockchain. It is also extremely secure since the amount of tokens needed to launch a 51% attack on the network would be a lot more expensive than any potential financial gains from attacking the network. However, PoS blockchains have similar scalability issues to PoW ones.

Projects

PoS is used by a multitude of blockchains like PIVX, Stratis, Lisk, Cardano, etc. It will eventually be used by Ethereum.

Pros: PoS is significantly more energy efficient than PoW. It also greatly increases the cost of a 51% attack when compared to PoW.[5]

Cons: scalability issues. In small communities, PoS mechanisms with no slash back can lead to nothing-at-stake attacks or collusion.

 

Delegated Proof of Stake (dPoS)

In a Delegated PoS system, every wallet that contains coins is able to vote for representatives. These representatives, called witnesses[6] validate transactions and form consensus amongst themselves, and are paid for their efforts through the system. Witnesses are responsible for creating blocks, while delegates (voted the exact same way), are responsible for maintaining the network and can propose changes.

Liquid Proof of Stake (Tezos)

Tezos’ consensus mechanism is a variant of the Proof of Stake, where the delegation of power is optional after being voted as a validator. The chances of being voted are based on the amount of coins stacked, but a validator can delegate his rights to validate to someone else if needed (e.g. lack of time, knowledge, or resources)[7].

Byzantine Fault Tolerant (Tendermint)

Tendermint also uses a variant of the PoS that adds a layer of participants in the consensus mechanism. Users can delegate their voting powers to the validator of their choice like in the regular PoS but there is no upper limit to the number of validator of a block (minimum of 4), making a block effectively final in about 3 seconds on average. The block is validated when more than ⅔ of the validators validate it. They get to that position by locking some coins, which are destroyed if an actor is found malicious or unreliable.

Scalability trilemma

Delegated PoS and its variants are all very scalable mechanisms due to the importance given to the main players (validators, slot leaders, voters etc). A bigger network will only strengthen the validity of these users. With incentives to do the work accurately, the network stays secure because these main players are always verified by others due to their privileged position. This centralizes the consensus – the algorithm is designed that way on purpose – in order to have a scalable and secure mechanism.

Projects

Delegated Proof of Stake is used by a variety of blockchains including EOS, DASH, NEO and many more.

Pros: dPoS is cost efficient and scalable. It also greatly increases the cost of a 51% attack when compared to PoW.[8]

Cons: In small communities, PoS mechanisms with no slash back can lead to nothing-at-stake attacks or collusion.

 

Directed Acyclic Graphs (DAG)

DAG is a directed graph data structure that uses a topological ordering. The sequence can only go from earlier to later. The distributed ledger combination with DAG comes from the idea of side-chains (different types of transactions are running on different chains simultaneously).

When each transaction is validated, it needs to be linked to an existing and relatively new transaction on the DAG network. If it links to earlier transactions every time, it would make the network too wide to validate the new transactions. Ideally, the DAG network chooses a transaction that happened recently to link to when a new transaction happens. The goal is to keep the network width within a certain range that can support quick transaction validation.

Consensus Mechanism 1

Due to its blockless nature, the transactions run directly into the DAG networks. The whole process is much faster than those of blockchains based on PoW and PoS.[9]

 

Unlike the blockchain model, however, DAG requires no miners to confirm each transaction as being authentic. Every new transaction that is submitted requires the confirmation of at least two earlier transactions before it is successfully recorded onto the network. By having two “parent transactions” confirm the validity of a subsequent transaction, human intervention becomes dispensable resulting in a vastly accelerated process: not requiring miners’ confirmation means transactions go through almost instantaneously.

Additionally, if there are no miners, there are no miners’ fees, helping to keep actual transaction fees to a minimum. It is also worth noting that this low-fee structure opens itself to another important feature; DAG’s ability to process microtransactions.

 

Tangle (IOTA)

Tangle is a DAG used by IOTA specialised in the machine-to-machine micropayment system. When a new transaction arrives, it must approve two previous transactions. If there is not a directed edge (approval) between transaction A and transaction B, but there is a directed path of length at least two from A to B, they say that A indirectly approves B.

The main idea of the tangle is the following: to issue a transaction, users must work to approve other transactions. Therefore, users who issue a transaction are contributing to the network’s security. It is assumed that the nodes check if the approved transactions are not conflicting. If a node finds that a transaction is in conflict with the tangle history, the node will not approve the conflicting transaction in either a direct or indirect manner.

For a node to issue a valid transaction, the node must solve a cryptographic puzzle similar to Bitcoin’s Proof of Work. It should also be noted that the tangle may contain conflicting transactions. The nodes do not have to achieve consensus on which valid transactions have the right to be in the ledger, meaning all of them can be in the tangle.

The main rule that the nodes use for deciding between two conflicting transactions is the following: a node runs an algorithm called the tip selection algorithm many times, and sees which of the two transactions is more likely to be indirectly approved. The algorithm’s idea is to place some particles, a.k.a. random walkers, on sites of the tangle and let them walk towards the tips (unapproved transactions in the tangle)  in a random way. The tips “chosen” by the walks are then the candidates for approval. For example, if a transaction was selected 97 times during 100 runs of the tip selection algorithm, they say that it is confirmed with 97% confidence.

 

Hashgraph  (Hedera)

Hashgraph also represents an alternative to a blockchain by having a similar but different design.

It has complete asynchrony, no leaders, no round robin, no proof-of-work and eventual consensus with probability one. It is based on a gossip protocol (a node communicates with a random one, then they both communicates to someone else, growing their numbers exponentially until the whole network is included), in which the participants don’t just gossip about transactions. They gossip about gossip.

Consensus Mechanism 4

The history of any gossip protocol can be represented by a graph where each member is one column of vertices. When Alice receives gossip from Bob, telling her everything he knows, that gossip event is represented by a vertex in the Alice column. In this way, if a single member becomes aware of new information, it will spread exponentially fast through the community until every member is aware of it.

If a community is simply gossiping signed transactions that they create, there is a certain amount of bandwidth required. If they instead gossip a hashgraph, then the overhead is minimal.

 

Block lattice – Nano

A block lattice is a novel type of DAG based architecture that was first introduced by the Nano cryptocurrency. With this type of architecture, each individual transacting on the network possesses their own blockchain, which is controlled by the individual’s private keys.

Each user’s blockchain tracks their account balance, rather than their transaction amounts. This method allows for less intensive storage requirements by means of database pruning. Each blockchain that is controlled by a user will also reflect information related to the individual’s balance history and can only be updated by the owner.

Transferring funds using Nano’s block lattice model results in two separate transactions. Balances are transferred between users’ blockchains through send and receive blocks, meaning that every transaction must come from a user and go to another one

 

Avalanche, Snowflake, Snowball (Perlin)

At a high level, the protocol achieves consensus by having each node ask k other nodes if a certain transaction happened (binary outcome) and base its own choice on what the majority voted. These nodes will then do the same, exponentially gaining consensus until every node aggrees.

It starts out in the worst possible scenario of a 50–50 split and after one round, with high probability, the scenario will no longer hold (chances of that are astronomically small after two rounds, even smaller after three). The protocol is designed to tip and not stay in the middle. As it tips more and more, the network’s perception shifts to one answer or the other.

The protocol is lightweight and therefore admits scalability and low latency (4 sec). The system can achieve high throughput (1300 tps), and scale well compared to existing systems that deliver similar functionality, while being able to have up to 50% of the nodes being Byzantine.

If an attacker tries to double spend, then the Avalanche protocol will not be able to decide between the two transactions, causing this money to be lost. Classical consensus and PoW protocols would have decided on one transaction or the other, however the Avalanche protocol might not; implicitly and naturally punishes bad actors without any additional complications to the protocol.

At a deeper level, the protocol actually goes from Slush to Snowflake to Snowball to Avalanche, with the above description being Slush.

Snowflake augments Slush with a single counter that captures the strength of a node’s conviction in its current decision. This per-node counter stores how many consecutive samples of the network have all chose the same vote (restarts with every change of decision). A node accepts the current color when its counter exceeds β, another security parameter. When the protocol is correctly parameterized for a given threshold of Byzantine nodes, it can ensure both safety and liveness.

Snowball augments Snowflake with confidence counters that capture the number of rounds that have yielded an unanime result for their corresponding decision. A node will switch sides when the confidence in its current vote becomes lower than the confidence value of a new vote.

Avalanche generalizes Snowball and maintains a DAG of all known transactions.

Regarding conflicting sets, Avalanche embodies a Snowball instance for each one of them. Avalanche takes advantage of the DAG structure and follow the transaction’s path. Specifically, when a transaction T is queried, all transactions reachable from T by following the DAG edges are implicitly part of the query. A node will only respond positively to the query if T and its entire ancestry are currently the preferred option in their respective conflict sets.

Scalability trilemma

A block lattice can theoretically scale across the whole planet in a decentralized way since it is not bound by its transactions but its users, and the fact that it is lighter than a blockchain because it stores account balances instead of transaction amounts. The fact that the security of each account-chain depends on the proof that the user picks makes this aspect less bullet-proof. It contains the strengths and weaknesses of all these proofs.

Pros: Faster, cheaper and lighter than traditional blockchains

Cons: Confirmation is needed for every transaction, making receiving microtransactions tedious

 

Threshold relay + probabilistic slot consensus

The Dfinity blockchain computer provides a secure, performant and flexible consensus mechanism. While first defined for a permissioned participation model, the consensus mechanism itself can be paired with any method of Sybil resistance (e.g. proof-of-work or proof-of-stake) to create an open participation model.

The Dfinity blockchain is layered on top of the Dfinity beacon and uses the beacon as its source of randomness for leader selection and leader ranking. They do so by building on top of their Threshold Relay technology which uses threshold signatures to quickly reach consensus among a selected set of miners over a peer to peer network. A threshold signature is a group signature that can only be constructed from the combined signatures of some threshold number of members, and thus represents cryptographic proof of agreement by at least that many members. The fact that the BLS group signatures in Dfinity always use the same signature bits, regardless of what subset of members contributed to it, allows the network to quickly reach consensus on a random number.

A “weight” is attributed to a chain based on the ranks of the leaders who proposed the blocks in the chain, and that weight is used to select between competing chains. The Dfinity blockchain is further hardened by a notarization process which dramatically improves the time to finality and eliminates the nothing-at-stake and selfish mining attacks.

Based on block weight, the Probability Slot Protocol allows replicas to decide which chain to build on when they propose a new block. Over time, this leads to probabilistic consensus on a chain prefix, where the probability of finality increases the more “weight” is added to a chain. This is analogous to proof-of-work chains, where the probability of finality increases the more “work” is added to a chain. A chain is only valid when built on blocks that have been notarized by group threshold signatures. Notarization in each block time quickly kills off lighter chains, enabling transaction confirmation times to be as low as 2 blocks.

Scalability trilemma

The consensus protocol created by Dfinity solves the scalability issues of PoW and PoS without having to reduce decentralization. However, Dfinity’s Blockchain Nervous System (BNS), while solving certain issues by auto-amending the blockchain, reduces overall security by making the ledger mutable. In other words, it is possible for information stored on the blockchain to be modified by the BNS.

Pros: Highly scalable, decentralized, can be implemented on different consensus like PoW and PoS, though it is currently built has an extension to Ethereum.

Cons: The BNS can at any point decide to change certain features like mining rewards, inflation, etc. without having to ask token holders beforehand.

 

Ripple consensus protocol

Nodes communicate and update proposals (block transactions) until a supermajority (80%) of peers agree on the same set of candidate transactions. During consensus, each node evaluates proposals from a specific set of peers, called chosen validators. Chosen validators represent a subset of the network which, when taken collectively, is “trusted” not to collude in an attempt to defraud the node evaluating the proposals.

When a round of consensus completes, each node computes a new ledger by applying the candidate transactions in the consensus transaction set to the last validated ledger. The validating nodes calculate a new version of the ledger and relay their results to the network, each sending a signed hash of the ledger. Nodes of the network recognize a ledger instance as validated when a supermajority of the peers have signed and broadcast the same validation hash.

Scalability trilemma

Ripple is very scalable because more users means more transactions validated and an overall more efficient network. It is however not decentralized because, while anyone can vote for or be a validator, it requires the aspiring validators to be part of a list controlled by Ripple thus limiting the choices of the users. The protocol also requires the users to trust the chosen validators to decide by supermajority the fate of transactions.

Pros: Low latency, very scalable and very low transaction costs.

Cons: All the validators that need to be trusted with the ecosystem come from a centralized entity

 

Stellar consensus protocol

Stellar is one of the few blockchain to have created their own consensus protocol. The Stellar Consensus Protocol (SCP) is the first provably safe consensus mechanism that simultaneously enjoys four key properties: decentralized control, low latency, flexible trust, and asymptotic security. It is a construction for a Federated Byzantine Agreement.

In a distributed system, a quorum is a set of nodes sufficient to reach agreement. Federated Byzantine agreement introduces the concept of a quorum slice, the subset of a quorum that can convince one particular node of agreement.

FBA brings open membership and decentralized control to Byzantine agreement. The key difference between a Byzantine agreement system and a federated Byzantine agreement system (FBAS) is that in FBA each node chooses its own quorum slices. The system-wide quorums result from these decisions by individual nodes. This means that in the SCP, individual nodes can choose which other participants they trust for information. The Trust is setup in a node’s config file.

In order to complete a transaction, a quorum (agreement) must be made by all parties.  For example, the nodes 7 and 8 are programmed to not trust banks. The different quorum slices and quorum form automatically by respecting the different config file of nodes.

Consensus Mechanism 3

Scalability trilemma

The SCP is focused mainly on scalability and security, putting less emphasis on decentralization. This is a consequence of the fact that only big companies are nodes in the Stellar Network and that each node can choose who to trust on the network.

Pros: Fast transaction speed, extremely low fees, highly scalable and secure.

Cons: Low level of decentralization because only big companies can be nodes and they can decide who to trust.

 

Algorand consensus protocol

Algorand uses a new Byzantine Agreement (BA) protocol to reach consensus among users on the next set of transactions. To scale the consensus to many users, Algorand uses a novel mechanism based on Verifiable Random Functions that allows users to privately check whether they are selected to participate in the BA to agree on the next set of transactions, and to include a proof of their selection in their network messages. In Algorand’s BA protocol, users do not keep any private state except for their private keys, which allows Algorand to replace participants immediately after they send a message. This mitigates targeted attacks on chosen participants after their identity is revealed.

To prevent Sybil attacks, Algorand assigns a weight to each user. BA is designed to guarantee
consensus as long as a weighted fraction (a constant greater than 2/3) of the users are honest. They weigh users based on the money in their account. Thus, as long as more than some fraction (over 2/3) of the money is owned by honest users, Algorand can avoid forks and double-spending.

BA gets to consensus by choosing a committee (a small set of representatives randomly selected from the total set of users, based on the users’ weights) to run each step of its protocol.

Scalability trilemma

In addition to being focused on scalability and security, Algorand is also decentralised to a certain extent. Using the amount of money that a user has to calculate his weight, thus his chances of being selected to create a block, brings a similar profile as Proof of Stake.

Pros: Mitigates most of the trilemma trade-offs

Cons: Someone with substantial capital could disrupt the chain

 

Other consensus mechanisms

A multitude of blockchains started using a variant on known proofs to fit their specific needs in order to achieve consensus more efficiently than with traditional methods.

 

Proof of elapsed time (PoET)

In a PoET, each node generates a random wait time and goes to sleep for that specified duration. The first one to wake up (the one with the shortest wait time) wakes up and commits a new block to the blockchain. The block creator is picked based on the random sleep time required and the results are verifiable by external participants and entities. The PoET leader election algorithm meets the criteria for a good lottery algorithm. It randomly distributes leadership election across the entire population of validators with distribution that is similar to what is provided by other lottery algorithms.[10]

Scalability trilemma

PoET focuses mainly on security and scalability. Indeed, it leverages trusted computing to enforce random waiting times for block construction without having the high computing requirements of regular PoW. On the other hand, it is quite centralized since miners are required to have Intel’s Software Guard Extension (SGX) to participate in the mining process. This means that they have to trust  a third party provider (Intel).

Projects

PoET is a relatively new consensus mechanism that is currently being used by Chia and Hyperledger Sawtooth.

Pros: It requires a lot less computing power than PoW since it allows a miners’ processors to “sleep” and switch to other tasks for the specified time thereby increasing its efficiency[11].

Cons: requires to trust a third party provider, requires specialized hardware

 

Proof of Space (PoSpace)

Proofs of space are very similar to proofs of work, except that instead of computation, storage is used. Proofs of Space are data which are useless for anything but generating the proof. Providing a proof to the network requires essentially no bandwidth. A proof of space can be thought of as a pre-commitment to keeping some storage unused because the blockchains utilize the idle storage space. The block creator is picked based on a percentage of his PoSpace out of the total idle space (process called farming instead of mining).

Scalability trilemma

Proof of Space is highly decentralized because it only requires miners to have a hard drive, which is something almost everyone has access to. It is also very secure because it would be extremely expensive for anyone to amass enough hard drive space to attack the blockchain. On the other hand, it suffers from the same scalability issues of the Proof of Work consensus mechanism.

Projects

There is currently a few projects using PoSpace, the most popular being BurstCoin, Chia and SpaceMint.

Pros: accessible for anyone, using hard drives is way more energy-efficient than using ASIC for mining.

Cons: scalability issues, an “arms race” is already underway in terms of storage space (hard drives in GBs are now irrelevant compared to those in TBs)

 

Proof of SpaceTime (PoST) – Filecoin

This Proof of SpaceTime is a perpetual proof of storage. A PoST allows a prover to convince a verifier that she spent a “space-time” resource (storing data—space—over a period of time)[12]. The proof relies on the fact that periodically (ie: every minute), there needs to be a proof that the data was stored. The PoST is a chronologically chained proof that the miners provide to create blocks because their probability of being elected is proportional to their storage currently in use in relation to the rest of the network.

Scalability trilemma

Similarly, to Proof of Space, PoST is focused mainly on decentralization and security, while still having scalability issues.

Pros: accessible to anyone with a hard drive, very secure. Compared to a proof-of-work, a PoST requires less energy use, as the “difficulty” can be increased by extending the time period over which data is stored without increasing computation costs.

Cons: scalability issues, an “arms race” is already underway in terms of storage space (hard drives in GBs are now irrelevant compared to those in TBs)

 

References for Consensus Mechanism

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https://dfinity.org/pdf-viewer/pdfs/viewer?file=../library/dfinity-consensus.pdf
https://medium.com/on-the-origin-of-smart-contract-platforms/on-the-origin-of-dfinity-526b4222eb4c
https://ripple.com/build/xrp-ledger-consensus-process/#consensus
https://www.stellar.org/papers/stellar-consensus-protocol.pdf
https://medium.com/a-stellar-journey/on-worldwide-consensus-359e9eb3e949
https://itnext.io/the-stellar-consensus-protocol-decentralization-explained-338b374d0d72
https://www.algorand.com/how-it-works/
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http://www.gibraltarlaw.com/directed-acyclic-graph-vs-blockchain/
https://assets.ctfassets.net/r1dr6vzfxhev/2t4uxvsIqk0EUau6g2sw0g/45eae33637ca92f85dd9f4a3a218e1ec/iota1_4_3.pdf
https://www.swirlds.com/downloads/SWIRLDS-TR-2016-01.pdf
https://www.mycryptopedia.com/nano-block-lattice-explained/   https://medium.com/zkcapital/demystifying-snowflake-to-avalanche-966f56c33fd7
https://ipfs.io/ipfs/QmUy4jh5mGNZvLkjies1RWM4YuvJh5o2FYopNPVYwrRVGV
https://www.investopedia.com/terms/p/proof-elapsed-time-cryptocurrency.asp
https://sawtooth.hyperledger.org/docs/core/nightly/0-8/introduction.html
https://www.investopedia.com/terms/p/proof-elapsed-time-cryptocurrency.asp
https://chia.net/faq/
https://filecoin.io/filecoin.pdf
https://eprint.iacr.org/2016/035.pdf

https://multicoin.capital/2018/02/23/models-scaling-trustless-computation/
https://cointelegraph.com/news/bittrex-to-delist-bitcoin-gold-by-mid-september-following-18-million-hack-of-btg-in-may
https://www.investopedia.com/terms/p/proof-stake-pos.asp
https://blockgeeks.com/guides/ethereum-casper/ https://notes.ethereum.org/SCIg8AH5SA-O4C1G1LYZHQ?view
https://decredible.com/mining/hybrid-consensus/
https://cardanodocs.com/cardano/proof-of-stake/
https://steemit.com/eos/@eosgo/understanding-eos-and-delegated-proof-of-stake
https://www.mycryptopedia.com/delegated-proof-stake-dpos-explained/
https://tezos.com/static/papers/position_paper.pdf
https://medium.com/@linda.xie/a-beginners-guide-to-tezos-c9618240183f
https://blog.cosmos.network/consensus-compare-tendermint-bft-vs-eos-dpos-46c5bca7204b?gi=d4637e741738
https://blog.usejournal.com/apples-to-apples-decred-is-20x-more-expensive-to-attack-than-bitcoin-68bafeb4546f
https://eprint.iacr.org/2016/199.pdf
https://dfinity.org/faq
https://medium.com/dfinity/dfinity-white-paper-our-consensus-algorithm-a11adc0a054c
https://dfinity.org/pdf-viewer/pdfs/viewer?file=../library/dfinity-consensus.pdf
https://medium.com/on-the-origin-of-smart-contract-platforms/on-the-origin-of-dfinity-526b4222eb4c

 

 

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