Note: This is the old version of the website. It will be taken offline on 01 May 2024. If there is anything on this website that you use and cannot find on the new version, please let me know at gregabc@learnme­abitxyzcoin.com.

  • Hash256
  • Hash160
  • Reverse Bytes
  • Hexadecimal
  • Satoshis

Private Key

A large randomly generated number.

A private key is a random number. It is a 256 bit number.

It is used as the source of a public key.

Try it! - Generate Private Key

32 bytes (64 characters)
Hexadecimal (Base 16)
Decimal (Base 10)
Binary (Base 2)

Never use a private key generated by a website or by someone else. Always generate your own private keys secretly on your own computer.

Generating a Private Key

All you need to generate a private key is a reliable source of randomness.

An easy source of randomness on a Linux computer is /dev/urandom, which provides random bits of data from your computer. All you need to do is read from it:

# generate 256 bits of random data
urandom = File.open("/dev/urandom")    # urandom is a "file"
bytes = urandom.read(32)               # read 32 bytes from it (256 bits)
privatekey = bytes.unpack("H*")[0]     # the data is binary, so unpack it to hexadecimal

# print the private key
puts privatekey

A private key can be almost any 256-bit number.

When you create a public key, your private key is put through a special mathematical function, and this function can only handle numbers up to just below 256 bits. The maximum value is:

max = 115792089237316195423570985008687907852837564279074904382605163141518161494336

This number is n-1, where n is the number of points on the elliptic curve used in Bitcoin. So when you generate a 256 bit number, you will want to check that it’s not above this maximum value.

Formats

A hexadecimal private key is 32 bytes (64 characters):

ef235aacf90d9f4aadd8c92e4b2562e1d9eb97f0df9ba3b508258739cb013db2

If you’re generating private keys for your own personal use, this is all you really need.

Wallet Import Format

However, you can convert your private key to a WIF Private Key, which basically makes it easier to copy and import in to wallets.

By Greg Walker,

Last Updated: 25 Aug 2020
  • 25 Aug 2020: Updated private key pages to indicate that a private key can be any number between 1 and (n-1) and not between 1 and (n), where n=115792089237316195423570985008687907852837564279074904382605163141518161494337 and is the order of the curve.
  • 21 Jul 2020: renamed /guide/ to /technical/
Back to Top

Hey there, it's Greg.

I'll let you know about cool website updates, or if something seriously interesting happens in bitcoin.


Don't worry, it doesn't happen very often.