Witness Script vs. Redeem Script

In Nested SegWit Multisig, the terminology can get confusing because there are two different "scripts" involved in a single transaction. Understanding the difference is key to auditing these transactions.

1. The P2SH Redeem Script

The Redeem Script is the 34-byte "Envelope" that sits in the ScriptSig.

• Role: It satisfies the legacy P2SH ScriptPubKey.

• Content: 00 20 [SHA256_HASH].

• Location: The Input data.

2. The P2WSH Witness Script

The Witness Script is the actual logic (e.g., the 2-of-3 multisig).

• Role: It is the "Real" smart contract.

• Content: OP_M [PubKeys] OP_N OP_CHECKMULTISIG.

• Location: The Witness Area (a separate part of the transaction).

3. The Relationship

Think of it like a set of nested boxes:

1. The ScriptPubKey looks for the hash of the Redeem Script.

2. The Redeem Script looks for the hash of the Witness Script.

3. The Witness Script looks for the Signatures.

4. Why this matters for fees

Because the large Witness Script (which contains all the public keys) is stored in the Witness area, it gets the 75% discount.

• In legacy multisig, the entire OP_M [Keys] OP_N script was in the Input, costing 4 WU per byte.

• In Nested Multisig, only the 34-byte pointer is in the Input. The massive keys are in the Witness, costing only 1 WU per byte.

Term	Also Known As	Content	Storage Location
Redeem Script	The Wrapper	00 20 [Hash]	ScriptSig (Input)
Witness Script	The Inner Script	OP_M [Keys] OP_N...	Witness Stack

In the next section, we will discuss the security implications of SHA256 vs. HASH160.