The Nested SegWit Redeem Script

To "Nest" SegWit inside a P2SH output, we use a very specific Redeem Script. This script acts as a cryptographic trapdoor: to an old node, it is just data, but to a new node, it is an instruction.

1. The Script Template

The Redeem Script for a P2SH-P2WPKH output is exactly 22 bytes long: 00 14 [20-Byte Public Key Hash]

• 00: This is the SegWit version byte (Version 0).

• 14: This is the push-data opcode (20 bytes).

• [20-Byte Hash]: This is the hash of the public key (exactly like in P2PKH).

2. On-Chain Footprint

When someone sends you Nested SegWit, they send to a standard P2SH ScriptPubKey: OP_HASH160 [20-Byte Hash of the 22-byte script] OP_EQUAL

Notice how small this is. The sender doesn't even know they are sending to a SegWit address.

3. The Unlocking Script (ScriptSig)

When you spend these coins, your ScriptSig must contain the 22-byte Redeem Script: 16 0014[20-byte-hash]

• 16: Hex for 22 (the length of the script).

• 0014...: The script itself.

4. Why 22 bytes?

The 22-byte format is the signal for BIP 141.

1. The BVM sees a P2SH spend.

2. It checks the hash. It matches.

3. It looks at the Redeem Script.

4. It says: "Wait, this is exactly 22 bytes and starts with 00 14. This is a SegWit spend!"

5. It then looks in the Witness field for the actual signature and public key.

Component	Length	Content
Witness Version	1 Byte	0x00
Push Opcode	1 Byte	0x14
PKH Data	20 Bytes	The Hashed Identity

In the next section, we will discuss Backward Compatibility Mechanics.