Nested SegWit Overview
P2SH-P2WPKH: Nested SegWit (The Transition Bridge)
When SegWit was introduced in 2017, the developers faced a major problem: many old wallets didn't know how to send to the new Bech32 (bc1...) addresses. To ensure everyone could benefit from the upgrade, they created Nested SegWit (P2SH-P2WPKH).
1. The Wrapper Concept
Nested SegWit is exactly what it sounds like: a SegWit transaction hidden inside a P2SH envelope.
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To an old wallet, it looks like a standard P2SH address starting with a 3.
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To a modern wallet, it is a signal to move the signatures to the Witness area and apply the 4:1 fee discount.
2. Why "Nest" it?
If you used a native SegWit address in 2017, you might find that an old exchange or wallet would say "Invalid Address." By using a Nested SegWit address:
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The old wallet sees a standard "3" address and sends the money.
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You, as the receiver, use a SegWit-compatible wallet to spend those coins.
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When you spend, you use the Witness field, saving on transaction fees.
3. The 3-Series Success
Nested SegWit is the reason why many "3" addresses are actually SegWit. While P2SH was originally for multisig, today a huge percentage of P2SH addresses are actually single-key Nested SegWit accounts.
4. Temporary but Critical
Nested SegWit was designed as a temporary transition phase. Today, as Bech32 (Native SegWit) and Taproot have become standard, Nested SegWit is being phased out in favor of even more efficient formats. However, it remains a brilliant example of how Bitcoin handles complex upgrades through backward compatibility.
| Feature | Legacy (P2PKH) | Nested SegWit | Native SegWit |
|---|---|---|---|
| Address | Starts with 1 | Starts with 3 | Starts with bc1q |
| Fee Savings | 0% | ~20-30% | ~30-40% |
| Compatibility | Universal | Universal | Improving |
| Structure | Standard | Wrapped | Direct |
In the next section, we will analyze the Redeem Script that makes this nesting possible.
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