Bech32m (The Taproot Standard)

When Taproot (P2TR) was developed, engineers discovered a subtle flaw in the original Bech32 checksum algorithm. This led to the creation of Bech32m (BIP350), the current standard for modern Bitcoin addresses.

1. The "q" vs. "p" Problem

The original Bech32 algorithm had a weakness: if you appended a q character (0) to the end of a string, the checksum wouldn't always change.

• In SegWit (v0), this wasn't a major issue because the data length was fixed.

• In future versions (like v1 Taproot), it could lead to situations where an invalid address might be accepted as valid.

2. The Solution: Bech32m

Bech32m is identical to Bech32 in every way, except for a tiny change in the constant used in the checksum math.

• Bech32 Constant: 1

• Bech32m Constant: 0x2be89091

This simple change completely eliminates the "Length Extension" vulnerability and ensures that Taproot addresses are as secure as possible.

3. The "p" Prefix

Taproot addresses are identified by the character p immediately after the bc1. Example: bc1p5d7rjAbCdEfGhIjKlMnOpQrStUvWxYz...

• The p tells the wallet this is a Witness Version 1 output.

• The wallet then uses the Bech32m math to verify the checksum instead of the old Bech32 math.

4. Compatibility

Modern Bitcoin nodes and wallets support both:

• Bech32 for version 0 (Starting with bc1q).

• Bech32m for version 1 and higher (Starting with bc1p). This allows the network to gradually transition to newer technology without breaking existing wallets.

5. Summary of Prefixes

Witness Version	Prefix	Encoding Standard	Script Type
None (Legacy)	1	Base58Check	P2PKH
None (Legacy)	3	Base58Check	P2SH
0	bc1q	Bech32	P2WPKH / P2WSH
1	bc1p	Bech32m	P2TR (Taproot)

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