BIP-38 · 6P… keys
Recovering a BIP-38 key password
If you have a piece of paper with a key starting 6P, you have a password-encrypted private key. It is the typical case of 2013–2017 paper wallets, and it is workable when you remember something about the password you set back then.
What you are holding
BIP-38 is a standard for encrypting a Bitcoin private key with a password, so the paper can be stored or even given away without whoever holds it being able to spend anything. There are two variants and the third character usually gives them away: non-multiplied ones start with 6PY, and EC-multiplied ones — those produced by paper wallet services using “intermediate codes” — with 6Pf or 6Pn. The variant changes the procedure, so it is the first thing I look at.
What protects the password
The derivation is scrypt, with parameters N=16384, r=8 and p=8. They are gentler on memory than the Ethereum keystore, but p=8 multiplies the work: on ordinary hardware the order of magnitude is between ten and a hundred guesses per second. It is a slow format, which is why what you remember matters more than hardware.
When there is a way out
- You remember the password in pieces, or the pattern you used at the time you printed the paper.
- They were “paper” passwords: many people set something memorable precisely because they knew they would not touch it for years.
- You can narrow the length or the character set.
- You know the associated address, which allows the balance to be confirmed and serves as proof of ownership.
When there is not
- The paper is incomplete or illegible: if one character of the encrypted key is missing the problem multiplies; if several are missing, there is no case.
- The password was random and you remember nothing.
- What you have does not start with
6Pbut with5,KorL: then it is not encrypted — it is a plaintext private key, and anyone who sees it can spend it. If that is your case, move the funds right now and do not show it to anybody, me included.
6P… key is encrypted, but it is a secret all the same: whoever holds it can try to guess the password with all the time in the world. Do not post it on a forum or paste it into a chat. In my procedure it is read out on a video call, like the rest of the secret material.