If you own your Bitcoin and keep the private keys of seed phrase, you rely largely on the mathematics and cryptography and a small part on yourself. But you can go a step further: create your own private seed phrase offline.
The extent to which your Bitcoin is safe has to do with two things. Firstly, how well you handle the keys, and secondly, the cryptographic class of the protocol. But did you know that you can make or come up with your own seed phrase?
Usually you also rely on the seeds that a wallet or other software generates for you. It uses randomness and entropy. But what if you don’t want to trust this? In such a case you can also use a 100% sovereign, safe and offline way to create your own seed phrase.
Estudio Bitcoin has explained step by step how this works. Read the English article for the extensive and complex story. For now, we will stick to a simpler Dutch representation of this method.
The basics: a private key
But first the basics. A Bitcoin Rejoin address is nothing more than the simplification of a public key. And this, in turn, is the result of passing the private key through an elliptical curve. We already described this algorithm and how it works in an explanation of ECDSA.
The private key, a sentence of characters or a series of 24 words, must be kept well. It is actually a randomly chosen value between 1 and 2²⁵⁶. That is a total of 115,792,089,237,316,195,423,570,985,008,687,907,853,269,984,665,640,564,039,457,584,007,913,129,639,936 values. And here you can make one yourself, if you don’t trust the entropy. You don’t need a Pseudo Random Number Generator or a True/Hardware Random Number Generator.
With a coin, pen and paper you can go a long way. Download and print the Coin-Seed pdf and you can start making your own seeds.
To generate good entropy for the seed phrase, give the euro coin a value of 0 for one side and a value of 1 for the other side. Header = 1 and Coin = 0. Then you are going to flip it 256 times to create a ‚256-bit seed of entropy‘. This whole process took the author of the source article 17 minutes.
Next, convert the 11 binary digits (the 1’s and 0’s) in each row to decimals. This can again be done 100% manually.
From Binary to Bitcoin
With a reminder you can add up the value of each row. It gives numbers between 0 and 2047. In this way you get 24 numbers with a value.
And so we end up with Bitcoin. The protocol has a Bitcoin Improvement Proposal that converts these 2048 words into seeds. This is BIP39. Please pay attention to whether the sequence starts with the numbering from 0 or from a 1.
You can then write down 23 words that you have composed yourself on the printed paper. For the last word you have to do something special. This is where 8 bits are still missing. This series includes a hash of the 256 bits of entropy you created with the coins. You can do this by hand, but an offline computer is easy. And in this way you fill the series with 24 words.
It is the probability of 1 out of 115,792,089,237,316,195,423,570,985,008,687,907,853,269,984,665,640,564,039,457,584,007,913,129,639,936 that someone has already used this exact sequence with exactly the same words.
You can then engrave these words into a seedplate or load them into a hardware wallet. And voila, you’ve created your own unique private key, giving you access to all the Bitcoin that belongs to corresponding addresses.