Wallet Import Format (WIF)

Wallet Import Format, or WIF, is a compact way of encoding a single bitcoin private key as a Base58Check string, typically 51 or 52 characters long, beginning with 5 for uncompressed keys or K or L for compressed ones. It exists so a key can be moved between wallets without transcription errors.

Why it matters

A raw private key is 32 bytes of entropy, hostile to human handling. WIF wraps it with a version prefix and a checksum, so a mistyped character produces a clean error instead of silently importing the wrong key. It was the workhorse of the paper wallet era, when users printed single keys for cold storage, and it still appears when sweeping old backups, physical bitcoin collectibles, or funds from legacy software.

Modern practice has moved to hierarchical deterministic wallets backed by seed phrases, which cover unlimited keys with one backup, so WIF today is mostly a compatibility and recovery format.

How it works

The encoder prepends the version byte 0x80 to the 32-byte key, appends a 0x01 flag if the corresponding public key is compressed, computes a checksum from a double SHA-256 hash, takes its first 4 bytes, and encodes the whole string in Base58. Importing reverses the process, and anyone who sees a WIF string has full control of that key's funds, so it must be handled like cash.