How to Encrypt your Bitcoin 12-word Backup using Cypher (Completely Offline) - Guide

I will cover way for securing your backup phrase using a cipher for encryption. This is a useful method for adding extra security to your passphrase. The benefit is that you can do this completely offline. Let's generate a sample wallet seed:

12-word seed: FLAG ELECTRIC POST DINOSAUR MIND OBVIOUS ABUSE HURRY THRIVE TRUTH POET GLASS

Let me introduce you to tabula recta also known as Autokey Cipher. This strangely looking square can be used for encrypting and decrypting words. On the first row, you can see the alphabet also know as the main alphabet. Each row below the main alphabet is called a cipher. There are 26 cipher alphabets, and each one is just one rightward shift from the previous one. Take a look:

How does it work? Our first task is to think of a keyword. We will use it for encryption and decryption. That's why it is important to remember the word of your choice and never share it with others. Let’s me start with an example.

We have chosen steemitbro as a keyword. There is one condition: Your keyword must be at least as long as the word you are encrypting. The first word in our 12-word seed is FLAG. We take the first letter from "steemitbro" and look for a cipher which starts with “S”. This means we will use cipher S for the encryption of the first letter in the word FLAG. We locate the letter F on the first row (primary alphabet) and look for the corresponding letter in the S cipher row which in our case is X. Repeat this task for all words and you will come up with the following nonsense: XEEK.

ORIGINAL	FLAG
KEYWORD	STEEMITBRO
ENCYPTED	XEEK

Let's repeat the task for the second letter in our first word: L. Now we need to also use the second letter in our keyword which is T. Here is an example:

Here is the final result after encryption:

XEEK WEIGFZBB HHWX VBRSEINS EBRH GUZMACL SUYWQ ZNVVK LAVMHM LKYXT HHIX YEEWE

Double check your encryption and don't forget your keyword. Now if somebody steals your 12-word backup his hands will be tied.

For decryption, we use the same logic as before. This time we only have the keyword "steemitbro" and the encrypted word XEEK. Here is an example decryption for the last letter of XEEK: K. The corresponding keyword letter would be E.

Please note that classical ciphers such as tabula recta are breakable with modern computers. The intent of this guide is to buy you some time in the case of a security breach. If somebody gains access to your 12-word seed please move your funds to a new wallet.