Base58

Base58 is a binary-to-text encoding scheme created for bitcoin by Satoshi Nakamoto. It represents data using 58 characters, the digits and letters of the alphanumeric set minus the easily confused 0, O, I, and l, and was used for bitcoin's original address and private key formats.

Why it matters

Bitcoin addresses are instructions for sending money, and a single mistyped character could send funds into the void. Base58 was designed for humans: by dropping look-alike characters and avoiding punctuation, it made addresses safer to transcribe, print, and read aloud. Legacy addresses beginning with 1, script addresses beginning with 3, and wallet import format private keys all use it, so it remains everywhere in bitcoin's landscape even as newer formats arrive.

How it works

The encoding treats the underlying bytes as one large number and repeatedly divides it by 58, mapping each remainder to a character in the alphabet. Bitcoin actually uses Base58Check, which first appends a 4-byte checksum derived from double SHA-256 hashing of the payload. If any character is mistyped, the checksum fails and wallet software rejects the address before money moves, catching errors with a failure probability of roughly 1 in 4 billion. The design's main weakness is inefficiency: case-sensitive mixed characters make Base58 strings poor candidates for compact QR codes, one reason the Bech32 format was later developed to replace it for modern address types.