by Adam Taché.
Foreword
This article will provide a comprehensive overview of the current state of the cryptocurrency ecosystem as of Summer 2018.
This includes high-level introductions and discussions on top current and upcoming projects: Bitcoin, Bitcoin Cash, Chia, Decred, smart contract platforms (Ethereum, DFINITY, Cosmos, EOS, Filecoin, Rchain, Tezos, Algorand), privacy coins (Zcash, Monero, Grin/MimbleWimble, Mobilecoin), and stablecoin projects (Basis, MakerDAO).
Bitcoin
Overview: Bitcoin is the original decentralized, programmable cryptocurrency and market leader, and was launched in January 2009 by anonymous developer(s) using the pseudonym Satoshi Nakamoto. It’s primarily referred to as “sound money” and digital gold; proponents believe it may eventually transcend the store of value function to become the world reserve currency and international standard of value, and others view it as a hedge against adverse macroeconomic scenarios.
Bitcoin has two main components: miners that solve computational problems using special-purpose chips through Proof-of-Work, and full nodes that store the blockchain and relay and validate transactions and blocks that miners build. The current roadmap emphasizes keeping blocks as small as possible to minimize the cost of trustlessly verifying blocks created by miners, and using the blockchain mostly as a settlement layer for settling any number of transactions from complex upper-layer systems into one.
The Bitcoin community views small blocks as essential to allow all users to verify transactions and enforce consensus rules, transact more privately, and to develop a constant back-log of transactions in the mempool to pay for miner security through transaction fees as inflation further decreases and leads to zero newly minted bitcoins per block.
Bitcoiners believe the killer-app of blockchain is already here: an uninflatable, dis-inflationary, censorship-resistant, fixed-supply asset that can’t be shut down by any governments and operates without any trusted-third parties on the most reliable financial system ever created. They view most alt-coin founders and crypto VCs as charlatans pumping digital ‘fools gold.’
“Any quantity of money in society is ‘optimal.’ Once a money is established, an increase in its supply confers no social benefit.” — Murray Rothbard
“SV has lost patience with BTC so moves on to shinier things, but BTC remains 99% of the value and a great opportunity for biz to emerge.” — Steve Lee, Former Product Director at Google
“The reason most new crypto investors hype the “utility hypothesis” is because you can’t get a 75% discount to the Bitcoin pre-sale.” — Arjun Balaji
The Lightning Network (LN) is a peer-to-peer network of trustless payment channels built using Bitcoin smart contracts, and is one proposed scalability solution to increase transaction throughput without sacrificing decentralization. Using the malleability fix from a 2017 update called SegWit, smart contracts enabling payment channels are now more easily implemented.
The LN allows any two users to open payment channels between each other from the main chain, and Hashed Timelock Contracts are used to route payments through other payment channels if the payer and payee don’t have a direct channel open. The LN is currently in beta with over 2000 nodes and 5000 channels already open, and certain LApps (Lightning Apps) that demonstrate the potential for micro-payments have been launched, such as Satoshi’s Place and Poketoshi.
Monetary Policy: There will only ever be 21 million bitcoins. The supply is dis-inflationary, with the rate of production halving roughly every four years or 210,000 blocks. Initially, 50 bitcoins were minted each block, and in 2020, this rate will half once again to 6.25 per block, with the last ever fraction of a new bitcoin expected to be minted in 2140.
Bitcoin Cash
Overview: Bitcoin Cash is a fork of Bitcoin that emphasizes increasing throughput on-chain, not off-chain. The roadmap includes steadily increasing the block size roughly every six months, with the system currently supporting a 32 MB block size. This limit is in comparison to Bitcoin’s 4 MB block weight limit, which has resulted in blocks greater than 2 MB.
Bitcoin Cash plans to incrementally scale toward unlimited block size, and the community does not believe in average users being able to afford validating blocks that miners produce. Proponents emphasize low transaction fees and encourage on-chain applications for increased utility, and spending and replacing BCH instead of just hodling. Developers are working on supporting on-chain tokenization, including ICOs and tokenized assets, such as through a Smart Contract Engine, as well as UTXO commitments.
Monetary Policy: Bitcoin Cash introduced a new difficulty adjustment algorithm (DAA) through a hard-fork that has resulted in ~90,000 more BCHs in existence in comparison to BTCs. It is also hard-capped at 21m.
Chia
Overview: Chia is an upcoming cryptocurrency led by Bram Cohen, the creator of BitTorrent and former developer at MojoNation, and is marketed as a “better” version of Bitcoin that can be more distributed, more secure, and greener.
The network is composed of full nodes that store the blockchain and relay transactions and blocks, and farmers (analogous to miners) that use Proof-of-Space and Proof-of-Time (Bram thinks Proof-of-Stake sucks and establishes a “decentralized centralized system” among the stakeholders, and he isn’t fond of the bonding and slashing dynamics) to leverage unutilized mass storage space around the globe instead of solving energy-intensive computational problems with Proof-of-Work.
“Storage is an over $100 billion a year industry with about 50% utilization”
For proof of space, farmers fill hard-drives with data as proof they allocated space for a challenge, then search for their best proof of space. Because proofs of space don’t cost (much) power, the chain would be vulnerable to what are called “grinding” attacks if only proof of space was used. For example, a farmer could attempt to re-farm the entire chain years after genesis, which would theoretically be possible given the rapid growth in hard-drive capacity in comparison to what would have been available when the chain started.
Chia solves the main grinding attack by alternating between proofs of space (parallelizable) and proofs of time (sequential). Proof-of-Time is formally known as Proof-of-Sequential-Work, or Verifiable Delay Algorithm, and is a special type of Proof-of-Work that requires a specific number of iterations, which proves a certain amount of wall-clock time (iterations, not actual time) has passed. Because VDA proves wall-clock time, a grinder could never catch up as it would take them two years to re-write two years of history.
For each block, farmers are to first work on a challenge for proof of space which requires taking a hash of the last proof of time and randomly mapping it to points on [0, 1], then a proof of time which finalizes the block. The “best” or closest proof of space point to the challenge is to finish first, as the number of iterations required to finish a proof of time is dependent on the result of the proof of space.
Proof-of-Time outputs a proof, which proves to verifiers that both a certain amount of time (iterations) was spent generating the output, and that the output is the right canonical output (the single correct output). VDA will likely produce a SNARK proof to speed up verification — Chia will require a trusted setup; if a fake setup is caught, the setup ceremony would have to be re-performed, but funds would not be at risk and the chain would operate normally with slower verification.
Chia will be based on the Bitcoin codebase, have Lightning Network compatibility, support MAST and SegWit, and is planning to start with Bitcoin Script before rolling out an upgradeable stack-based Chia Script with BLS Signatures (instead of ECDSA or Schnorr) and a new set of op-codes including new flow controls. Bram noted that he’s a fan of the Bitcoin Core roadmap and wants Chia to never have to hard-fork.
Monetary Policy: Mostly unknown to the public. Mini pre-IPO. Plans to offer equity to public, non-accredited investors, potentially distributing part of its massive pre-mine to share holders. Permanently inflationary.
Decred
Overview: Decred is a cryptocurrency known for its hybrid Proof-of-Work and Proof-of-Stake protocol, and was launched in December 2016. The main distinguishing factor of Decred is its community-driven on-chain governance structure, which aims to give shareholders a say in consensus and future hard-forks to the system.
“Decred’s killer feature is good governance, and with good governance, you can have any feature you want.” — Placeholder
All users are able to participate in governance through a staking process. Users purchase “tickets” using DCR, which requires locking the value of tokens into a lottery pool for a certain amount of time (~28 days on average) and paying a ticket fee to incentivize miners to include the purchase in a block. The ticket price is determined by an algorithm akin to a staking difficulty.
Each block, a lottery runs which picks five random tickets. The winning stakeholders are required to vote to approve that the block a miner proposed is valid; three of five votes are required for the state-change to be recorded to the blockchain, and stakeholders must be online to vote. The tickets expire after ~142 days or 40,960 blocks; if the stakeholder is never randomly chosen to vote, they receive back their initial deposit.
This staking process is not only used to vote on the validty of miner blocks. Winning stakeholders are also able to vote on any changes to the system. When a consensus rule change is proposed for the network, there is a 8064 block long (~28 days) voting window. If over this time 75% of stakeholder votes and 75% of hash power signal the change, the hard-fork is approved and users must update their software to apply the fork.
As a reward for voting, each stakeholder receives 6% of the block reward. PoW miners receive 60%, and the remaining 10% is reserved for a development subsidy. If stakerholders reject a block, the PoW and development rewards are not paid out.
The 2018 Decred roadmap includes Lightning Network compatability, a new proposal system called Politeia to create a time-stamped public repository of user proposals, a decentralized exchange, Decentralized Autonomous Entities, and scalability improvements.
Monetary Policy: Decred has a fixed-supply of 21 million coins. The supply schedule differs from Bitcoin in that the genesis block subsidy started at ~31.2 coins/block, and the subsidy reduces by a factor of 100/101 every ~21.33 days. There are currently 7.15 million DCR tokens circulating, of which over 45% is being staked.
Smart Contract Platforms
Ethereum
Overview: Ethereum is a virtual computer spearheaded by Vitalik Buterin. It aims to be a “decentralized world computer” by offering a more extensible, (nearly) Turing-Complete smart contract capability in comparison to Bitcoin Script’s Turing-Incomplete smart contracts. Ethereum did not opt for the UTXO model of coins; instead, Ethereum has accounts and contracts with balances. Unlike Bitcoin where all transactions cost roughly the same for miners to execute, Ethereum contracts have highly differing levels of complexity in terms of bandwidth, storage, and computation. For this reason, Ethereum opted for a gas model in which each transaction is priced depending on a cost per quantity of gas consumed by the miners to execute contracts. Miners are able to dynamically adjust the gas limit that the system supports by a certain factor each block, which is analogous to the block size in Bitcoin.
The network is currently composed of miners, full nodes, a_nd light nodes._ Light nodes rely on full nodes for security and can validate state relevant to the user by downloading block headers from the longest PoW chain, and full nodes are mostly composed of go-ethereum (geth) and Parity nodes. These offer full or “fast/warp” syncing, and pruning modes. A subset of full nodes are fully archival nodes, which fully validate all miner blocks, execute all contracts, and store the entire blockchain state. Ethereum offers many token standards: ERC-20 for platform tokens and ERC-721 for non-fungible tokens like collectibles being the most prominent.
The current roadmap for Ethereum includes three fundamental design changes: sharding, a new consensus protocol called Casper, and replacing the Ethereum Virtual Machine (EVM) with the eWASM. The eWASM will allow developers to write smart contracts using high-level programming languages that compile down to Wasm (Web Assembly) instead of using Ethereum’s current JavaScript-like Solidity language.
The most significant change coming to Ethereum over the next two years is Casper+Sharding, which is Ethereum’s proposal to (mostly) switch from Proof-of-Work to Proof-of-Stake (as part of Casper), and break up state of the network into a bunch of partitions called shards. Each shard would have independent state and transaction history, and all validators on the network wouldn’t be responsible for handling all transactions; instead, notaries within each shard would be responsible for their own shard. Cross-shard transacting and shards of shards are both possible. There is a proposal to integrate BLS Signatures and zk-STARKs for verification to aid scalability.
Casper developers have “learned to love” weak subjectivity and aim to simulate the security of PoW through threats of economic penalties for validators (slashing dishonest actors by taking away deposits) instead of burning energy. They think it’s possible to design a PoS protocol that is more secure, decentralized, offers faster block times, finality, and is more flexible than PoW, which is “limited” by physics.
Ethereum has been highly criticized by Bitcoiners for introducing toxic speculation into the cryptocurrency ecosystem through ICOs and promoting increased centralization of validation over time. Vitalik and other Ethereum developers do not believe in cheap fully validating nodes for average users.
Ethereum dApps currently have very few DAUs (Daily Active Users) despite there being tens of thousands of DADs (Daily Active Developers), of which most are Solidity developers, not protocol developers. The Ethereum community is much more optimistic; members have noted that most dApps are not yet launched and that criticizing an early-stage blockchain for lack of DAU is futile, as they believe DADs is an accurate predictor for future DAUs and that “killer apps are coming.” They are excited about various current and upcoming projects, such as Plasma, Plasma Cash, the Raiden Network, generalized state channels, off-chain computations, sidechains like DAppChains, lending, games, financial derivatives, 0x, and more.
Monetary Policy: The exact monetary policy is not currently known. Eventually, Ethereum is expected to have either a 0.5%-2% inflation rate per year or a hard-cap of ether. Vitalik recently proposed a hard-cap, but Vlad Zamfir disagreed, and the topic is being debated within Ethereum research. Ethereum was originally launched through an ICO, but was deemed not a security by the SEC.
DFINITY
Overview: DFINITY is an upcoming competitor to Ethereum’s “blockchain computer” throne aiming to launch Q4 2018. The engineering team is extremely experienced with distributed systems and cryptography, and is aiming to build a much more performant, scalable, and secure decentralized computer that eventually offers unlimited computational capacity.
In DFINITY the “Code is Law” is contingent upon the decisions of the nervous system. The omnipotence of the BNS is highly important. AI is Law.
DFINITY is known for its “Blockchain Nervous System” governance model (liquid democracy) in which a distributed intelligence is to act as a benevolent superuser for managing and integrating changes to the protocol. The goals for BNS are to allow for a rapid upgrade process in comparison to traditional blockchains, be able to adjust economic parameters if needed (such as number of tokens required for staking deposit), increase the value of dfinity tokens, and perform mitigation of thefts (in cases such as Bitcoin’s Mt Gox exchange and Ethereum DAO hacks) without human intervention using its privileged control over token ownership (including freezing accounts) and ability to execute arbitrary code.
The BNS will be guided by a human market process where constitution-directed “neurons” can create proposals and vote for changes. Voting power is proportional to deposits of dfinities to the BNS, and neurons can earn rewards and autonomously vote by tapping into the directed trust graph of neurons. The BNS is to analyze the “moral authority” behind proposals.
At a high-level, the DFINITY blockchain is built on top of a decentralized randomness beacon acting as a Verifiable Random Function (VRF) and verifiable heartbeat of the system. This allows randomness to be used for both the consensus process and the application layers. The system is composed of a network of processes that includes miners and a p2p broadcast network composed of an unlimited amount of clients with permanent pseudonymous identities. The broadcast network is organized into random groups, which can send messages to everyone else. Dfinity is Ethereum compatible; Ethereum code can run on DFINITY.
The consensus mechanism is Threshold Relay, where a group is assigned a public key through a generation method to sign messages using BLS threshold signatures if a certain threshold of group members agree. The signatures produced are random numbers using the VRF, which can be used to select a next group. This threshold process is used for notarizing blocks (time-stamping and proving publication), which allows for a block time of only a few seconds and finality after two confirmations or roughly six seconds. It prioritizes consistency over availability, and eliminates selfish mining and the nothing at stake problem for its Proof-of-Stake sybil resistance, and will be used to facilitate sharding and validation towers. Shards act as the storage layer, receive transactions, record updates to their local state, then pass the transactions to validation towers, which execute contracts (written in Solidity and high-level languages compiled to WASM) and validate transactions.
Monetary Policy: The majority (52.93%) of the tokens are owned by the DFINITY foundation, team, and for partnerships. 45.82% of tokens were sold to investors in a pre-sale. The remainder (1.25%) were distributed through a community airdrop.
Cosmos
Overview: Cosmos is an upcoming ecosystem marketed as the internet of blockchains, and will be a network of independent, interoperable blockchains divided into hubs with zones. The main hub is the Cosmos Hub, which is a blockchain powered by the Atom staking token. The independent blockchains with their own tokens are called zones, and there can be any number of hubs with their own public or private zones. Hubs connect to zones using the IBC (inter-blockchain communication) protocol, which allows tokens to be sent from one zone to another. Cosmos is expected to launch in 2018 and is said to support thousands of transactions per second (tps) within its zones.
The Cosmos team developed Tendermint, which they call a general-purpose blockchain consensus engine, and powers a peer-to-peer gossip protocol and traditional Byzantine Fault Tolerant (BFT) consensus protocols, which allow for up to 1/3 of machines to fail. Tendermint will power Cosmos’ Proof-of-Stake, and offers developers an Application-Blockchain Interface (ABCI) to write smart contracts in any programming language.
Cosmos will have a transactional token for payments, which is currently called the Photon, and is to be rewarded to validators (who bond Atoms) and used to pay fees for zones that accept it. There’s a proposal to distribute photons to ether holders through a “hard spoon” of Ethereum, which will create Ethermint, a PoS EVM zone with mirrored account balances of Ethereum’s.
Tendermint hosts a weakly synchronous round-based voting system where validators bond atoms as collateral, propose blocks, signal intent, then sign to commit new blocks. It requires 2/3s of validators to commit to a block, prioritizes consistency over availability, and allows for 1–3 second finality when fully operational. Tendermint is a delegated system which only supports 100 validators participating at a time. Delegators participate in consensus, police validators, and share revenue with their chosen validators through a commission rate.
Monetary Policy: Cosmos conducted an ICO, which raised $16m in BTC and ETH for over 60% of the initial atoms for fundraiser participants. The inflation rate of atoms will be dynamically adjusted by the Cosmos Hub to be between 7% and 21%.
EOS
Overview: EOS is the latest general purpose, Turing-Complete smart contract platform to launch, and is Dan Larimer’s third blockchain. EOS sacrifices decentralization and censorship-reistance for speed and high throughput, and uses inflation to pay for network security to enable zero fee payments for users. It uses a BFT Delegated Proof-of-Stake (dPoS) model — invented by Larimer — for consensus and as part of on-chain governance. 21 pseudonymous Block Producers (BPs) are voted in by delegates that hold EOS tokens, and are to abide by the (evolvable) EOS constitution. The BPs also host a replicated storage service using IPFS for token holders.
Block time is roughly half a second, finality is achieved within two seconds, and the platform can supposedly handle thousands of tps. Contracts are compiled down to WASM, accounts are human-readable usernames, and the platform offers protocol-level account recovery through account recovery partners.
The launch and election process for EOS were notoriously messy; the platform was plagued with low voter turnout until a large whale with over 5% of tokens cast a vote, the platform crashed for over five hours the first week, and BPs have already frozen 34 user accounts. Despite the rough launch, some investors are optimistic that the project finds a niche for applications in need of a high throughput blockchain without sovereign-grade censorship resistance. Block.one raised over $4b in the EOS ICO, and has over $1b of ecosystem funds to help the blockchain grow. There are dozens of air-drops planned for EOS token holders.
Monetary Policy: Token holders can vote on inflation rates; the default is currently 5% per year.
Filecoin
Overview: Filecoin is a work-in-progress blockchain that aims to be a decentralized, highly efficient, and robust storage network (DSN) to challenge traditional cloud platforms, such as Amazon S3, Google Storage, and Microsoft Azure Cloud Storage. It aims to scale to ZB and beyond through economic incentives by allowing users to profit from offering hard-drive space, analogous to Bitcoin scaling security to over 40 TH/s through incentives for providing hash rate. It will also support generic smart contracts.
Various platforms, such as the upcoming personal operating system and personal server Urbit, have identified a lingering problem with the modern web: all of your personal data is stored on centralized private servers, and the data is not guaranteed to last forever. Filecoin is built around IPFS, a peer-to-peer distributed web protocol, and plans on building bridges to provide file storage and retrieval for other networks, such as to allow Ethereum contracts to use Filecoin, and integration with Bitcoin and ZCash.
Filecoin aims to offer a formally verified protocol and (stateful) smart contracts using SNARKs, as well as proofs of when data is stored, that data is still stored, and that participants can actually extract the data. Proofs-of-Storage, such as Proofs of Replication, Data Possession, and Retrievability, would allow a prover to prove to a verifier that data is stored and replicated and for the verifier to retrieve the data from the proofs to prevent withholdings.
Filecoin aims to facilitate storage and retrieval markets with bids and asks that allow price undercutting and tiers of service within mining; for example, tiered read access would allow for differing rewards for differing levels of caching, well-placed (physical) nodes, and for optimized low latency and high bandwidth nodes. Filecoin plans to launch purely on-chain markets initially and develop state channels in the future.
The network is broken up into clients (users) which hire miners to store their data, miners, and a network that organizes work, verifies and repairs corrupted storage using erasure coding (analogous to a RAID array), and rewards miners enacting correct behavior with Filecoins proportionately to their power metric, which measures how much useful storage miners are providing. Miners participate in consensus through a “useful” Proof-of-Work algorithm by generating Proofs-of-Spacetime to allow the network to audit storage offered by miners overtime, and consensus is to be achieved using rounds of miner elections where the probability of a miner being elected is proportional to its provided storage. Proofs-of-Spacetime are added to the chain if a majority of the power in the network deem them valid.
Some are skeptical that Filecoin (and the other blockchain storage networks, such as Storj and Sia) can compete with the centralized alternatives due to problems with speed, access control, reliability, volatility, and the marketplace UI/UX.
Monetary Policy: There will be a finite 2 billion Filecoins, with 70% to be mined and released through a smoother exponential decay curve in comparison to Bitcoin and ZCash. The rest are to be distributed to investors through an ICO which raised $257m, and to the Filecoin Foundation and Protocol Labs (the team).
RChain
Overview: RChain is a work-in-progress virtual computer aiming to be a highly scalable, concurrent, and performant blockchain offering general-purpose, formally verified, Turing-Complete smart contracts, and has a democratic cooperative governance structure. RChain is unique because its architecture is based on a computational model called Rho-Calculus, as opposed to a machine with a von Neumann architecture like the serialized Ethereum Virtual Machine. RChain aims to support 40,000–100,000 tps.
Rho-Calculus supports 4 C’s: completeness, compositionality (making larger programs out of smaller programs), concurrency, and complexity (being able to measure computations using resources). RChain contracts are programmed using the concurrent and functional Rholang language, which focuses on message-passing, runs on the Rho Virtual Machine (RhoVM), and is formally modeled using rho-calculus. Contracts are paid for using the RChain Phlogiston token (analogous to gas in Ethereum), and the main staking token is called the RChain Rev.
The network is broken up into nodes that each run the RChain environment and communicate between each other. The RhoVM Execution Environment runs on the JVM (Java Virtual Machine) and runs multiple RhoVMs on each node; each VM executes a smart contract, which run concurrently and are multi-threaded.
RChain uses a Proof-of-Stake protocol similar to Ethereum’s Casper for Sybil resistance, and sharding (resulting in multiple parallel and synchronizable blockchains that can communicate over channels), concurrency, and security come as part of the ρ-calculus model.
Monetary Policy: RChain raised ~$30m in an ICO. There is a fixed supply of 861,185,194 RChain tokens, which are currently ERC-20 but will be 1:1 converted when the blockchain launches. The team owns 30%, 20% were burned, and the co-op owns ~7%.
Tezos
Overview: Tezos is a long-awaited blockchain that has been under development since 2014, and is aiming to support formally-verified smart contracts through a stack-based programming language called Michelsen. It is marketed as a “self-amending crypto-ledger,” which is a reference to the ability for stake holders to “self-upgrade” the protocol through an on-chain governance mechanism.
In terms of the network, the main components are:
- Bakers (stakers) that participate in consensus through a BFT Delegated Proof-of-Stake (dPoS) model by staking bonds, create and validate blocks when randomly chosen, and are paid through transaction fees and bonds.
- Endorsers (delegates) that are required to safety deposit bonds to get rewarded, and give powers to another account to bake for them and generate and sign blocks for them.
- Nodes which relay and validate blocks and transactions and store the blockchain state.
Tezos chose not to pursue sharding for scaling, and although they are initially starting with a low gas limit per block, the developers do not believe in cheap validation for all and want to scale to large block sizes. They plan to eventually use recursive SNARKs to allow users to sync the blockchain from scratch and validate it from the genesis block in less than one second; in order to do this, each block would be a hash of the merkle root of the content of the block, and a proof that the state transition was valid (similar to Coda’s succint blockchain design).
Monetary Policy: There is a 5% inflation rate per year with an initial supply of 763,306,930 tokens, with a possibility of a future hard-cap.
Algorand
Overview: Algorand is an upcoming project, led by MIT professor and Turing Award Laueate Silvio Micali, that aims to be a highly scalable, censorship-resistant blockchain that is partition resilient and achieves block finality in one minute. A new Byzantine Agreement called BA★ is used to achieve consensus on state transitions, and Proof-of-Stake is employed for Sybil resistance; users are weighted based on their token ownership, and a small set of users — called a committee — is chosen to perform each step of the protocol, with other users voting on the proposed values.
Similarly to DFINITY, Algorand uses a Verifiable Random Function (VRF) to employ randomness within the protocol, and does so for committee selection. Through a process called “cryptographic sortition,” each user selects themselves for each committee by running a lottery, and propagates proof they are selected if they win, as well as a priority for other users to determine which of potentially multiple blocks they should accept.
Algorand avoids targeted attacks on chosen participants by replacing the participant at each step, and as long as a 2/3 weight of the token ownership is honest, the chain has a negligible proability of forking and guarantees of agreement and consistency. Unlike other PoS protocols, Algorand does not slash malicious actor deposits if they propose an illicit state for the ledger. There is also a set of leaders for project governance.
Monetary Policy: Unknown. Upcoming token sale.
Privacy Coins
Zcash
Overview: Founded by Zooko and other cryptographers in 2016, Zcash is an implementation of the Zerocash protocol. As a privacy-centric cryptocurrency, Zcash is the leader in zero-knowledge (ZK) cryptography. Zcash is the first blockchain to use zk-SNARKs (Succinct Non-interactive ARguments of Knowledge, a zero-knowledge proof of knowledge), which were invented by scientists on the team. Zcash was built using the Bitcoin codebase, and required a one-time trusted multi-party computation ceremony to generate public parameters for SNARKs using air-gapped computers.
zk-SNARK proofs allow fully encrypted information to be verified by validators without the validators being able to access the unencrypted data. They facilitate z-transactions, also known as shielded transactions, where balance and address data are hidden from the network. The sender of a shielded transaction constructs a small proof that currently takes up to 40 seconds to generate but can be verified in a few milliseconds.
Zcash also supports non-anonymous t(ransparent)-transactions, which have been shown to reduce the anonymity of shielded transactions through linkability. In the future with speed improvements of zk-SNARK technology, it is expected that the percentage of shielded transactions will increase from the current ~31.5% usage.
Upcoming upgrade called Sapling for faster zk-SNARKs, following Overwinter.
Zcash currently uses Proof-of-Work, although it seems Zooko and the team would be willing to switch to a provably secure alternative protocol, such as a Proof-of-Stake variant. Zcash also plans to upgrade zk-SNARKs to a more scalable, quantum-safe zero-knowledge variant called zk-STARKs, which don’t require a trusted setup. Block time is 2.5 minutes, and the maximum block size is 2 MB.
Monetary Policy: ZCash has an identical monetary policy as Bitcoin (21 million maximum coins). It was launched in late 2016, so only 4.1 million coins have been mined. 10% of all coins will be awarded to the Zcash Company — founders, investors, employees, and advisors — from block rewards.
Monero
Overview: Monero is a private cryptocurrency that was launched in April 2014 by anonymous developer(s) using the pseudonym Nicolas van Saberhagen. Unlike Zcash, Monero does not support non-anonymous transactions; all origins, destinations, and amounts are completely obfuscated, and thus Monero tokens are fungible.
Monero uses one-time ring signatures to hide the sender, ring confidential transactions (RingCT) to hide transaction amounts, stealth addresses to hide the receiver, and has two minute block times. It is built using the CryptoNote protocol, which implements a dynamic block size with a cap on growth rate. Monero is mined using Proof-of-Work, and the developers are attempting an ASIC-resistant scheme by changing the PoW algorithm roughly every six months. The last PoW change was in April, and the hash rate is still recovering; it’s currently 60% lower than at its all time high. The latest update added Ledger hardware wallet support and made compact blocks called fluffy blocks default.
Monetary Policy: There are ~16.1m XMR in existence, and the main emission schedule will issue ~18.4m XMR until the year 2022. After that, a “tail emission” curve kicks in where 0.3 XMR will be issued per minute (157,680 per year).
Grin and MimbleWimble
Overview: MimbleWimble is a design for a massively-prunable, scalable blockchain-based ledger dropped into a Bitcoin IRC chat in 2016 by pseudonymous engineer(s) named Tom Elvis Jedusor. Grin is an upcoming cryptocurrency that is an implementation of MimbleWimble using Rust. Grin uses a Proof-of-Work algorithm called Cuckoo Cycle which is supposed to be fairly resistant to a Bitcoin-style ASIC arms-race, and is being developed by mostly pseudonymous engineers using other Harry Potter character names, such as Ignotus Peverell. MimbleWimble can also be implemented as a Bitcoin side-chain, or soft-forked in as an extension block.
MimbleWimble supports confidential transactions to encrypt the amounts of all transaction data via homomorphic encryption and uses rangeproofs for validity, but does not support scripting. Instead, properties of Elliptic Curve Cryptography were used to enable multi-signature transactions, atomic swaps, time-locked transactions and outputs, and the Lightning Network.
With Bitcoin, new validators that join the network have to sync from the genesis block and validate that each and every transaction has been valid. With MimbleWimble, new validators only need block headers, unspent outputs, and excess data (transaction data recording the difference between outputs and inputs, and signatures of which only one is created for all parties involved in a transaction). Transactions are indistinguishable from one another; there are no addresses or amounts.
Monetary Policy: Grin plans to emit a new coin every second forever. There is a currently a test net, and the coin plans to launch this year.
Mobilecoin
Overview: MobileCoin is an upcoming privacy-centric cryptocurrency advised by the founder of Signal, Moxie Marlinspike. MobileCoin is mobile-first, hence the prefix mobile; the idea is to integrate MobileCoin wallets into messaging applications, such as Signal, WhatsApp, and Facebook Messenger, and to allow cheap, fast payments, and key management and recovery using a PIN.
MobileCoin uses Stellar’s Consensus Protocol (SCP), which is a Federated Byzantine Agreement (FBA) that prioritizes safety. The goal is for a set of nodes, called a quorum, to obtain global consensus for state changes. Nodes select their own subset of the quorum, called a quorum slice, based on arbitrary conditions like reputation. The quorum slices vote to convince their nodes of arbitrary statements, and individual quorum slices can fail without the entire network failing. MobileCoin also uses CryptoNote addresses and ring-signatures for transaction anonymity. Nodes are to be run in SGX secure enclaves as one layer of security.
Monetary Policy: Fixed supply. More details unknown.
Stablecoins
Stablecoins are cryptocurrencies that attempt to maintain a stable price; most currently attempt to peg their price to 1 US Dollar, but they could theoretically attempt a peg to anything, such as a basket of goods. A number of people have described a functional stablecoin as the “holy grail” of the cryptocurrency realm, and others are extremely skeptical they will ever work without collapsing.
Volatility of existing cryptocurrencies has detracted from their potential use as global media of exchange and day-to-day currencies. It is expected that a functional stablecoin would immediately be usable as a store of value, medium of exchange, and unit of account, regardless of its size and age. This is unlike regular cryptocurrencies, which would require a long monetization period and massive market cap to become relatively stable.
There exist three major kinds of stablecoins. The most common and arguably the simplest kind are fiat-collateralized stablecoins, which include Tether (USDT) and TrueUSD (TUSD), and attempt a peg to a unit of fiat (e.g. 1 USD). Fiat-collateralized stablecoins are expected to be stable, with the assumption that the backing is legitimate and regularly audited. They are highly centralized and are necessarily tied to existing financial institutions and banks.
Another kind of stablecoin is the crypto-collateralized stablecoin, and one prominent example is MakerDAO’s DAI. Crypto-collateralized stablecoins attempt to maintain their stability through over collateralizing the stablecoins with another cryptocurrency, such as ETH, and utilizing a trading bot to maintain the desired peg.
The third type of stablecoin is a non-collateralized / algorithmic kind. These stablecoins are not explicitly backed by any underlying collateral; instead, their algorithms conduct active, automated monetary policy (i.e. expansions and contractions of supply to keep the stablecoin price pegged to $1). These systems can be decentralized; however, they are still susceptible to large death spirals if the demand for the overall system drops too suddenly.
MakerDAO
Overview: MakerDAO is one of the most prominent Decentralized Autonomous Organizations (DAOs) built on the Ethereum blockchain. One of their core products is the DAI stablecoin, which is a “crypto-collateralized” stablecoin.
The system is composed of both MKR tokens and DAI tokens; the former represents ownership in the system and allows owners to participate in governance decisions, and the latter is the actual stablecoin. The system attempts to constantly peg the value of the DAI token to $1, and uses collateral to back its value and algorithmic interest rate adjustments to stabilize its price.
The peg is maintained by modifying the incentives for borrowing and holding DAI. Notably, DAI requires at least 1.5x worth of ETH to be deposited in order to receive 1x worth of DAI stablecoins. The system is decentralized and uses a series of oracles to provide smart contracts price data from exchanges; however, it requires a high cost of capital and is mildly susceptible to black swan price drops in the underlying asset.
The cost of borrowing DAI becomes more expensive when the price is below its target. If the price rises above target, then the cost of creating new DAI is reduced. These forces act to either decrease or increase the total supply of DAI, ensuring that the asset has low volatility. The stability of DAI is also supported by liquidating collateralized debt positions when the underlying collateral falls too far in value. When this happens, the collateral needs to be sold off to cover the outstanding DAI backed by it.
Basis
Overview: Basis is a stablecoin expected to launch in 2018, having raised $133M+ in funding in the Spring of 2018 from a wide variety of prominent investors in the crypto space. Basis describes itself as an “Algorithmic Central Bank.” By utilizing a relatively complex three-token system composed of stablecoins (Basis), bonds (Restore Tokens) and shares (Growth Tokens), Basis attempts to utilize what is described as an Algorithmic Monetary Policy to keep the Basis price pegged to $1.
Basis will be using a to-be-defined oracle system for the blockchain to continuously receive the current stablecoin price across global cryptocurrency exchanges. Basis plans to expand the supply of stablecoins when the coins are in high demand and the price goes above $1.00, and contract the supply by auctioning off bonds when there is a drop in demand and the price goes below $1.00. It promises to return a full Basis stablecoin to bond holders when the price returns to $1.00.
In this way, Basis is inspired by the existing central banking techniques, and attempts to bring the proven monetary methods of central banks and combine them with the transparency and decentralization potential of blockchain technology. Base shares provide ownership in the entire system. They are described as “like owning a piece of the Fed,” and the Basis system is often described as a Private Central Bank. Base shares receive newly issued stablecoins whenever the demand for the stablecoin increases and the supply expands.
If the Basis system ever gets big enough where it is used globally as a medium of exchange, or even widely accepted for goods and services, Basis would be able to peg the stablecoin to a basket of goods / a CPI Index, rather than the US Dollar.