With over 50 privacy coins on the market, purveyors of anonymous transactions are spoilt for choice. This smorgasbord of privacy-centric coins can be a little overwhelming though. To help you pick the best of the bunch, here's our rundown of the main contenders.

How Privacy Coins Work

Bitcoin transactions are semi-anonymous: every transaction on the blockchain is broadcast publicly and visible for all eternity, but the owner of each wallet is unknown. Tying addresses to real-world identities is now relatively easy for the powers-that-be, because everyone has to cash out somewhere, and that usually involves linking bitcoin addresses to bank accounts.

Most privacy coins still rely on a bitcoin-style public ledger, but use technology that obfuscates the path of the transaction. It might still be possible to determine that a certain amount of cryptocurrency was sent, but the path leading from sender to recipient has been concealed. The way in which various privacy coins go about this differs considerably.

Privacy Tech Algorithms

The three most common privacy algorithms are zk-Snarks, Coinjoin, and RingCT. The latter method is used in monero; Coinjoin features in dash and is also being trialed with bitcoin; and zk-Snarks are used by most of the Z coins including Zcash. Here's how they work:

RingCT: Monero's ring signatures allow the sender to hide their transaction among other outputs. In addition, RingCT makes it possible to hide the amount being sent. Coupled with a stealth receiving address, this makes for an extremely discreet way of sending funds. Transparency is optional with monero, which uses an "opaque" blockchain.

How monero's RingCT works.

Coinjoin: Developed by Gregory Maxwell, Coinjoin deploys a 'safety in numbers' approach. When two senders despatch a transaction of an identical amount, this is converted into a joint payment. When this occurs, correlating the transaction inputs and outputs is virtually impossible. There are many variants of Coinjoin including Private Send, which is used by dash, and Coin Shuffle; Cash Shuffle is the version currently being tested with bitcoin cash.

zk-Snarks: Zero-Knowledge Succinct Non-Interactive Argument of Knowledge is a technology that allows miners to verify transactions without knowing who sent or received the coins. Using a cryptographic hash, each party can prove that a certain statement is true without revealing the precise details of who sent what and where. Although most commonly associated with the Zerocoin family, zk-Snarks are also being tested with ethereum.

The Main Privacy Players

Several of the most popular privacy coins have since forked, creating additional flavors of privacy coin. These spin-offs tend to use the same privacy algorithm but add additional features. We'll consider some of these forks shortly, but first let's examine the big two in the privacy war.

Everything You Ever Wanted to Know About Privacy CoinsZcash: Born out of the Zerocoin protocol, Zcash is basically bitcoin with the option of privacy. There's a fixed supply of 21 million coins (sound familiar?) and despite using a public blockchain, Zcash allows for the sender, recipient, and amount being sent all to be concealed. Researchers have published evidence that suggests some Zcash transactions can be de-anonymized, though for everyday usage, Zcash should still provide enough privacy for most people.

To date, Zcash is mostly being used as a regular cryptocurrency, with only a small portion of users enabling its privacy features. Tellingly, Zcash doesn't have much by way of deep web adoption, a realm whose users are especially paranoid about privacy.

Everything You Ever Wanted to Know About Privacy CoinsMonero: Like Zcash, monero has emerged as a viable cryptocurrency in its own right, even for individuals who aren't interested in privacy. Its privacy tech is highly regarded and numerous deep web marketplaces accept monero. Monero usage surged in the wake of the Alphabay shutdown, after it emerged that feds were unable to determine how much XMR the site's alleged kingpin, Alexandre Cazes, held.

A string of deep web dealers were busted this year after their bitcoin transactions were tied to their real-world identities, and it was around then that monero cemented itself as the darknet's privacy coin of choice. SHUM – Should Have Used Monero – is the default reply on r/darknetmarkets any time another vendor is busted.

The Forked Contenders

The Zerocoin protocol has spawned a slew of Z-named coins, most of which forked from Zcash. There isn't space to detail them all, but the following two are particularly interesting.

Zclassic: ZCL forked from Zcash over concerns that Zcash had an excessive pre-mine. Zclassic has since forged its own path and is currently one of the hottest privacy tokens in town. ZCL has rocketed in value this week due to the forthcoming launch of Bitcoin Private. This is a fork which aims to combine the best bits of bitcoin and Zclassic. Because Bitcoin Private will be available to holders of Zclassic, buyers have bundled into ZCL, pushing its price to over $100, in readiness for the free Bitcoin Private coins they stand to receive at the time of the fork.

Everything You Ever Wanted to Know About Privacy CoinsZencash: ZEN is a fork of Zclassic – that's right, a fork of a fork – but it's got some interesting features, not least encrypted messaging. Like dash, zencash uses nodes as an additional means of securing its network; there are currently almost 5,000 ZEN Secure Nodes in operation. ZEN is a community-oriented project that utilizes many of the principles governing a DAO, and the nascent privacy coin seems to have a solid roadmap in place.

The Hopefuls

The following coins have privacy features either enabled as standard or as an optional extra and are also worthy of consideration.

Dash: By market cap, dash is the biggest coin on this list. It's not an outright privacy coin however, but does have Private Send for users who'd prefer to keep their business to themselves.

Everything You Ever Wanted to Know About Privacy CoinsZcoin: The other Z worth mentioning, Zcoin enables users to "mint" a coin on a public ledger so as to transform it into a private coin. This process can be repeated multiple times, allowing a coin to be sent publicly or privately as desired.

Pivx: An open source project, Pivx is another community-oriented privacy coin. It uses a mixing mechanism that's based on Coinjoin, but which operates in a decentralized manner, aided by a network of masternodes.

Everything You Ever Wanted to Know About Privacy CoinsVerge: XVG is another anonymous cryptocurrency that was designed for privacy-friendly networks such as Tor and I2P. The general consensus is that verge isn't as private as some of its competitors, so don't trust it with your life. On the plus side, it boasts fast and low-cost transactions.

The Rest of the Pack

Unfortunately there isn't space to delve into the inner workings of every privacy coin on the market. When it comes to the likes of Navcoin, Hcash, Cloakcoin, Stealthcoin, Hush, Zoin, Spectrecoin and all the rest, you'll need to do your own research and assess the merits of each coin's privacy tech. With over 50 coins to choose from, you could be reading for some time. This Twitter thread rounds up the rest of the chasing pack.

How to Ensure Complete Privacy

Buying a privacy coin doesn't mean you now operate under a cloak of invisibility. From browser fingerprinting to recording IP addresses, there are various ways in which three-letter agencies can de-anonymize supposedly private transactions. Unless you're a drug lord or a terrorist, though, they've probably got better things to do with their time. In situations where absolute privacy is essential, there are mixers such as Bitmixer and Join Market that can be used to tumble coins and obfuscate their origins.

When using monero, some users split their transaction into multiple hops, often passing through Shape Shift from a different altcoin and then on to an Electrum wallet using Tails. There's no such thing as perfect privacy on the web, but privacy coins make it a lot easier to send and receive funds without broadcasting your business to the world. Expect to see many more privacy-centric coins entering the market in 2018 as the battle for privacy heats up.