“The year is 2021. It is no longer safe to transmit information. Phones, computers and satellites are all vulnerable. But there is a solution. Input the data into the brain of a human courier like Johnny Mnemonic!”
That’s from the trailer for the prophetic 1995 sci-fi thriller starring Keanu Reeves, Johnny Mnemonic. With a few revisions, including knocking 6 years off the time, this trailer would make a fantastic introduction to bitcoin brain wallets.
As long as you have a working memory, a bitcoin brain wallet can be the most secure form of storing your bitcoin. But in order to understand what a brain wallet is and how to create one, we need to first understand what it means to “store bitcoin”.
Storing bitcoins digitally, physically, mentally
Bitcoins don’t really exist. There are no digital files that can be called bitcoins. There are no serial numbers associated with particular bitcoins. What exists is a digital ledger that keeps track of bitcoin addresses and how many bitcoins are associated with each one.
But there aren’t any bitcoins in those addresses. The addresses only contain a figure that represents an amount of bitcoin. Again, there are no bitcoins, only addresses that contain amounts of them.
Each address has a private key that allows access to an address in order to transfer the part or all of the balance into another address.
When people talk about storing bitcoin, they’re talking about storing a private key. When someone has bitcoin stolen, what they mean is that their private key(s) were stolen and the addresses associated with those private keys were emptied, the bitcoin amounts transferred to another address controlled by the thief.
Standard bitcoin wallets are software that store private keys. They offer varying degrees of security based on the structure of their code and encryption.
Paper wallets are simply private keys written/printed (stored) on a piece of paper. Their security depends on how well the piece of paper is kept safe. Theoretically, bitcoin paper wallets are immune from being hacked. They are, however, susceptible to being stolen like cash or snatched remotely as in the case of the Bloomberg News reporter who showed his paper wallet QR code directly to the television camera.
A brain wallet is a private key put (stored) to memory. No digital file with a private key, no piece of paper printed with a private key. Only a mush of brain material containing the string of characters that allows you access to an address in the ledger.
You forget your brain wallet, you lose your bitcoins. Simple as that.
Creating brain wallet that’s easy to remember, but hard to crack
Now, a brain wallet can be the private key itself, but most people would find it difficult to memorize a string of characters that look like this:
So, the easiest way to create a brain wallet is to create a unique passphrase and put it through a hash algorithm that produces a private key like the one above (which is then put through a hash algorithm to yield the public key). Fortunately, there are tools that can help us do that such as BitAddress.org.
We made the private key above by using the passphrase: What is a bitcoin brain wallet and how to create one, or how do I become Johnny Mnemonic – this is not the type of passphrase you want to use because it exists as the name of post on the internet. In fact, you shouldn’t use anything that appears in literature or lyrics. The passphrase should be completely unique. Ideally with misspellings and irregular punctuation.
Again, a bitcoin brain wallet is only secure if your passphrase is completely unique and contains a high level of entropy. And it should be long. Remember, you’re not up against a human. You’re up against computers that can test trillions of combinations in the snap of a finger. The name of your dog with an exclamation point instead of the letter ‘i’ is not going to cut it.
Here’s an example of a good passphrase: i witch when i am ooold…,,,thebiggestboatonland is The great Tit@nic and it’s a vegetarian
Now, you just need to remember this passphrase instead of the private key it yields, which can created by passing it through a SHA256 (Secure Hashing Algorithm) or using the brain wallet tool on BitAddress.org:
The public address from this private key is also created by passing the string through a SHA256, the BitAddress.org tool will also give you this:
So now we’re all set. We’ve got our passphrase, private key (which is derived from the passphrase and no longer needs to be stored), and our public address to which bitcoin can now be transferred.
Is it safe? The dangers of a brain wallet
If you watched the Johnny Mnemonic trailer, there’s an exchange near the end that goes like this:
Johnny Mnemonic: I’m a dead man if I don’t get this out of my head.
Buddy: I can get it out.
Johnny Mnemonic: How?
Buddy: With a cranial drill and a pair of forceps.
The idea is that you can digitally secure information through encryption, however information in your memory can only be secured by deception. A properly created brain wallet is not susceptible to hacking, however it is susceptible to invasive surgery (in Mnemonic’s case) and coercion or torture.
If you have a brain wallet, don’t tell anyone.