Serialization and Prefixes (ypub, zpub)

While the original BIP32 standard only defined xpub and xprv, the evolution of Bitcoin (SegWit) required new ways to tell wallets which type of address to generate from an extended key. This led to the creation of the SLIP-132 standard.

1. The Standard Prefix: xpub

An xpub (Mainnet) always starts with the characters xpub.

• Default Behavior: In most older wallets, an xpub will generate Legacy (P2PKH) addresses starting with a 1.

2. The SegWit Prefixes

To help wallets know they should generate SegWit addresses, different version bytes were introduced:

ypub (Nested SegWit)

• Prefix: ypub

• Address Type: P2SH-P2WPKH (Starts with a 3).

• Version Byte: 0x049d7cb2

zpub (Native SegWit)

• Prefix: zpub

• Address Type: Bech32 (P2WPKH) (Starts with bc1q).

• Version Byte: 0x04b24746

3. Why the prefixes matter?

The internal math of the key is exactly the same whether it starts with x, y, or z. The only difference is the Version Byte at the beginning.

• The Benefit: If you import a zpub into a wallet like Electrum or BlueWallet, the software automatically knows to show you your bc1q balances.

• The Problem: If you import an xpub but you were actually using Native SegWit, the wallet might show a balance of Zero because it is looking at the wrong set of (Legacy) addresses.

4. The Table of SLIP-132

Prefix	Script Type	Address Format
xpub	P2PKH	1... (Legacy)
ypub	P2SH-P2WPKH	3... (Nested SegWit)
zpub	P2WPKH	bc1q... (Native SegWit)
Ypub	P2WSH	Multisig Nested SegWit
Zpub	P2WSH	Multisig Native SegWit

In the final section, we will build a Python Extended Key Auditor.