Base58Check (The Legacy Standard)

Base58Check was the first address encoding standard created for Bitcoin. It was specifically designed to be easy for humans to read and type while providing a robust defense against transcription errors.

1. Why Base58?

Standard Base64 encoding includes characters that look identical in many fonts. To prevent user error, Satoshi created Base58 by removing:

• 0 (Number Zero)

• O (Capital O)

• I (Capital I)

• l (Lowercase L)

• + and / (Non-alphanumeric characters)

The result is a set of 58 characters that are distinct and easy to tell apart even on small screens or printed paper.

2. The "Check" in Base58Check

An address is not just a base58 string. It includes a mathematical Checksum.

1. Payload: The version byte + the HASH160.

2. Double SHA256: Hash the payload twice.

3. Truncate: Take the first 4 bytes of that hash.

4. Append: Attach those 4 bytes to the end of the payload.

5. Encode: Convert the whole thing to Base58.

3. Typo Protection

Because of those 4 checksum bytes, if you change a single character in the address, the math will no longer "Check Out."

• A wallet will recognize that the checksum doesn't match the payload.

• It will refuse to send the transaction, saving the user from losing funds due to a typo.

4. Version Prefixes

The first byte of the payload determines the starting character of the address.

• 0x00: Results in an address starting with 1 (P2PKH).

• 0x05: Results in an address starting with 3 (P2SH).

Component	Size (Bytes)	Description
Version	1	Identifies the network and type.
Payload	20	The Public Key Hash (HASH160).
Checksum	4	Error detection code.
Total	25	Raw data before encoding.

In the next section, we will look at the modern Bech32 standard.