Bech32

Bech32, specified in BIP173, is the address encoding introduced for native Segregated Witness. It replaced Base58Check for witness outputs and is used by SegWit version 0 types such as P2WPKH and P2WSH, whose mainnet addresses begin with bc1q. A Bech32 string has three parts: a human-readable prefix (bc for mainnet, tb for testnet), a separator 1, and a Base32 data section ending in a six-character checksum.

Why it was designed

The character set deliberately excludes 1, b, i, and o to reduce visual ambiguity, and addresses are all-lowercase, which makes them compact in QR codes and easier to read aloud. The checksum uses a BCH code that guarantees detection of any error affecting up to four characters and catches larger errors with overwhelming probability, so a single mistyped character almost never produces a valid but wrong address.

Practical notes

Because Bech32 is case-insensitive, wallets may display it in uppercase for denser QR codes while accepting lowercase input. A subtle flaw, where inserting or deleting q characters before a final p could preserve the checksum, led to a refined variant for later witness versions. Self-custody operators reading addresses aloud or transcribing them benefit directly from Bech32's error-detection guarantees.

The refined successor used by Taproot is Bech32m, and the output type it encodes is P2WPKH (Native SegWit).