Standard Bitcoin transactions only require one signature, from the owner of the private key associated with the Bitcoin address. However, the Bitcoin network supports much more complicated transactions, which require multiple signatures to authorize.
Bitcoin multisignature addresses can have up to 15 associated private keys, although the most common is 3. The idea is that Bitcoins become “encumbered,” requiring the cooperation of separate parties in order to do anything with them. In a typical multisig situation, 2 out of 3 key holders need to authorize a transaction.
While a multisig wallet may not be the best choice for every bitcoin user, there simply isn't a substitute when security is the primary concern. They let 2 people from the same business complete a third-party payment; one person generates a transaction while a second authorizes the payment. They also allow individual users to implement two-factor authentication, where one key is on your primary computer and a second is on your smartphone, so the funds cannot be spent without a signature from both devices.
P2SH.info keeps track of the number of bitcoins being held in 'pay to script hash' addresses, which account for most of the multisignature addresses is use. According to the service, about 10 percent of all bitcoins are currently being held in multisignature wallets, or 1.5 Million bitcoins today.
This means that only 10 percent of all existing bitcoins, at most, are being secured as well as they could be. If you've got a large stash of coins, and aren't one of those 10 percent, it may be time for you to pick one of the many wallets that provide multisig security.
The following 13 wallets are the only ones we could find today that offer multisignature addresses, and still appear to be supported. All have differing features, as they seem to solve slightly different problems, so it’s worth taking your time when choosing one.
Armory and mSigna assume that you aren't as safe as you can be without a local copy of the whole blockchain. While this is true for a very specific type of attack, it's over 50 Gigabytes in size, and keeping it up to date means running the local machine 24/7. Other wallet makers vary in how they remotely sign transactions, while some don't sign it at all, giving you all of the keys. Each of these differences need to be carefully considered.
Armory is the original high-security wallet, developed way back in mid-2011. It has many unique options, but they can be more than a little overbearing for new users. It requires a local copy of the blockchain to be on the same machine, and it specializes in splitting your wallet in two. The 'watch-only' wallet has no private keys inside it, while the 'cold wallet' is intended to live on a different computer that never goes online.
There is no web portal nor signing service with Armory, but the wallet can be configured with up to 7 keys. It's also the only wallet here to help you make paper wallets, for storing your coins totally on paper, even multiple pieces of paper for multisignature wallets.
Bitalo is a web-only wallet, and one of the least-known services on this list. Its lack of an open-source software client likely scares away quite a few of the security purists, but it comes with a full suite of adjoined services like an exchange, marketplace, classifieds, mining pool, and even a prediction market - which are all integrated with your wallet service on their site.
Bitalo allows for an optional 2-factor authentication, but if you don't turn it on you won't have any way for them to sign their key for you, so it's a necessity when dealing with multiple keys.
BitGo is one of the very largest wallet providers no matter how you measure. They also offer free insurance to all users in case of a hack.
You may find yourself using a BitGo wallet without even knowing it, as they are the only wallet on this list that integrates into third-party bitcoin exchanges and other financial services.
Block.io is a simple web-only wallet that also holds a few other altcoins like Doge and Litecoin, and has a very well-developed API for programmers. Unfortunately, they don't offer an open source client, nor allow you to generate your own private keys locally.
Block.io uses 'Green Addressing,' which is a way to build up a sort of white list for familiar bitcoin addresses, which will save you money on transaction fees if you're a repeat sender. Although nothing has been proven wrong about this practice, there have been many criticisms about green addressing over the years, and some point to the fact that many services in the past that used it, including Mt.Gox, are now out of business.
Blocktrail is a popular mobile wallet with a pretty, open source phone app that keeps one key and gives you two, so you can back one up off the phone and have full control when you need it. Two-factor authentication is optional.
When it's time to spend some coins on Blocktrail, it sends your one signed key and then a password to them that unlocks your encrypted key that they're holding onto, on the server, just for the one spend. That way they never really have any of your keys, but they hold onto one that is encrypted from them. This can be very secure but it relies on you remembering a password for this extra layer of security.
The most popular wallet on the list by far, Coinbase is more than a wallet service, it's like a bank and exchange all rolled into one, with local websites and bank connections in 30 countries worldwide.
There is no such thing as anonymity while using Coinbase, and their client code is not open source in any way. They normally offer Insurance to their customers, but in the case of Multisignature “vaults” as they call them, they don't offer insurance anymore because they don't have full control over your coins that way. They do offer some interesting combinations for their multisignature addresses though, up to 3-of-6 with a variety of options for two-factor authentication on top of that.
The best reason to use Coinbase would be for the convenience of using their Shift debit card, but it does not appear that the Shift card will spend coins from a multisignature vault, only a normal wallet inside your Coinbase account.
Coinkite is a unique wallet in that it has the most options to experiment with, a powerful API and even tools and hardware for merchants. Starting with their ability to go all the way up to a 15-of-15 multisignature wallet, to integration with the Ledger hardware wallet, you can make a very safe and full-featured wallet with Coinkite.
It's only a web-based wallet, but the helpful company built around it and numerous options on their website make it seem like a full enterprise solution, even just for an individual's wallet.
Copay is a simple but very well-built wallet, that is available on many different platforms. It was developed specifically for multisignature use by the BitPay development team, and you can build and use up to 6-of-6 address wallets. They've even integrated the Trezor and Ledger hardware into Copay already.
They have added secure payment verification to these sleek little wallets, so especially while moving your funds, there is less reason to fear losing them by sending them to the wrong address.
Electrum is the most popular desktop-only wallet and the first to use Simple Payment Verification (SPV) as described by Satoshi in his whitepaper. That means that it only downloads the header for each block, which doesn't take long at all, so it's more secure than a web wallet while being almost as fast to use.
This high-privacy wallet has a reputation as the wallet of choice for the dark web, and has been constantly developed since 2011. It has the most hardware wallets integrated of all wallets, and it's enjoyed a huge following ever since before it was included as the standard privacy wallet on all Tails installs.
It's also the only desktop-only client software that uses a 3rd-party service for key signing. TrustedCoin is a service provider that has been integrated into the software so that you can optionally choose a specific but powerful level of security. They call this two-factor authorization, but it's actually an instance of a 2-of-3 key multisignature wallet where TrustedCoin holds the 3rd key, you hold the other two, and they charge you a tiny fee to spend with them each time.
GreenAddress is a popular wallet that has some great features that no one else has picked up yet. For starters, it's got the widest array of customizable 'triggers,' which tell the software when it's ok to sign your transaction with their remote key. It’s also the only wallet that has been developed for every major platform, so it's optimized for whatever device you're using now.
As their name implies, they use green addresses to help save on your transaction fee costs. That can be a mixed blessing, but so far this wallet is building up quite a following and has even spun off a colored-coin wallet called GreenBits. With hardware support for both the Ledger and the Trezor, no other multisig wallets come as well-rounded as this one does.
mSIGNA is the other 'old school' desktop-only wallet that uses a local blockchain, much like Armory does. It lets you make up to 8-of-8 key multisignature wallets though. Unlike Armory, you can generate a seed phrase to backup your wallet in a different way if needed.
The local blockchain appears to be an optional setting however, and in stark contrast to Armory, opening up the mSIGNA client can be a very speedy for a local software client.
Huobi's QuickWallet is mainly only popular in China, but offers an English version that has some strong features. This web-only wallet doesn't appear to have made its code open-source anywhere, although it may have been programmed in Chinese and simply hard to find.
It's the only wallet here that requires using Google Authenticator in order to have their key sign your transactions, which makes the service less anonymous because Google needs a phone number for that service.
Finally, Xapo is another popular bitcoin bank similar to Coinbase, and therefore needs your full identification. Xapo is, however, one of only two on our list that offers insurance on a multisignature wallet account.
There are many different trigger choices for initiating a spend, but multisig wallets are limited to only 2-of-3 keys. A Xapo debit card is also available, like Coinbases' Shift card, but it can't be shipped to US residents.