P2SH-P2WSH: Nested SegWit Multisig

P2SH-P2WSH (Nested SegWit Multisig) is the more advanced sibling of the single-key Nested SegWit format. It allows organizations and power users to run complex multisig wallets with lower fees while maintaining compatibility with legacy Bitcoin "3" addresses.

1. Multi-Layer Security

Nested SegWit Multisig uses a three-layer "Matryoshka doll" structure:

1. Layer 1 (The P2SH Wrapper): A standard address starting with 3.

2. Layer 2 (The P2WSH Signal): A 34-byte script that tells the network to use the Witness logic.

3. Layer 3 (The Witness Script): The actual M-of-N multisig logic.

2. Why Use Nested Multisig?

In 2017 and 2018, many multisig hardware wallets and institutional custody providers were slow to adopt the new Bech32 (bc1...) addresses. Nested SegWit Multisig allowed them to:

• Save Money: Multisig transactions are large. Moving the signatures to the Witness field provided massive fee savings (often 40-50% for complex scripts).

• Compatibility: They could still receive funds from old exchanges that only understood "1" and "3" addresses.

3. The 34-Byte Identifier

While single-key Nested SegWit uses a 22-byte script, Multisig Nested SegWit uses a 34-byte script. This difference is critical for nodes to know whether they are looking for a public key or a complex script hash.

4. The Legacy Standard

For several years, P2SH-P2WSH was the "Gold Standard" for institutional Bitcoin storage. It combined the battle-tested security of P2SH with the modern efficiency of SegWit.

Feature	Legacy Multisig (P2SH)	Nested SegWit Multisig	Native SegWit Multisig
Address	Starts with 3	Starts with 3	Starts with bc1q
Hash Size	20 Bytes (HASH160)	32 Bytes (SHA256)	32 Bytes (SHA256)
Fee Savings	0%	~40-50%	~50-60%
Structure	Script in Input	Script in Witness	Script in Witness

In the next section, we will analyze the 34-byte Redeem Script.