Commit-Reveal vs Dual-Layer Scripts: The Real Architecture of Bitcoin Script

Companion notes to my book Mastering Taproot.

HODLing is the beginning.

But Bitcoin was meant to be programmed.



"Not Just HODLing: Real Bitcoin Script Engineering" starts here.

Bitcoin Script looks like a single program. It isn’t.

Underneath, two different architectures coexist:

• a philosophical commit–reveal model shared by all address types




• an engineering dual-layer structure introduced only in P2SH, P2WSH, and Taproot script-path

Most confusion comes from mixing these two.

This essay separates them cleanly.

1. The Universal Truth: Commit → Reveal

Every Bitcoin output — P2PKH, SegWit, Taproot — follows one rule:

Lock:   commit to a condition

Unlock: reveal a proof satisfying it

• P2PKH commits to a pubkey hash




• P2SH commits to a script hash




• P2WSH commits to SHA256(script)




• Taproot commits to a tweaked key (optionally hiding a Merkle tree)

This is a conceptual model, not an execution structure.

Commit–reveal is the language. Opcodes are the grammar.

2. Single-Layer vs Dual-Layer Scripts

Commit–reveal is universal. Dual-layer execution is not.

Bitcoin has exactly two script architectures:

Single-Layer Scripts

Used by:

• P2PK / P2PKH




• P2MS (bare multisig)




• P2WPKH




• Taproot key-path

Structure:

scriptSig / witness pushes data

            ↓

scriptPubKey (or implicit logic) executes directly

No script hash. No script extraction. No inner vs outer.

P2WPKH

Witness only carries data. Nodes recognize OP_0 <20 bytes>, then execute an implicit P2PKH-equivalent program.

This is not dual-layer because there is no script hash and no revealed script.

Taproot key-path

Pure single-layer: a single Schnorr signature verifies the tweaked key. No script execution at all.

Dual-Layer Scripts

Used only by:

• P2SH




• P2WSH




• Taproot script-path

Architecture:

Outer layer:   verify a commitment (hash / tweaked key)

Inner layer:   execute the revealed script

┌─────────────────────────────┐

│        Outer Commit Layer   │

│   (scriptPubKey commitment) │

└───────────────┬─────────────┘

                │

                ▼

┌─────────────────────────────┐

│      Inner Execution Layer  │

│ (redeemScript / witnessScript / tapscript)

└─────────────────────────────┘

Only these three structures follow: unlock → reveal → load script → execute script.

This is why P2SH has no OP_CHECKSIG in its locking script. All logic lives in the inner script.

3. The Commitment Types

P2SH

scriptPubKey:  OP_HASH160 <script_hash> OP_EQUAL

redeemScript:  (actual logic, e.g. OP_CHECKSIG)

P2WSH

scriptPubKey:  OP_0 <32-byte script_hash>

witnessScript: (actual logic)

Taproot script-path

scriptPubKey:  OP_1 <32-byte output_pubkey>

witness:       <stack> <tapscript> <control_block>

The control_block contains the internal key and Merkle path.

The outer script never encodes logic — only a fingerprint of logic.

4. Why This Distinction Matters

Failing to distinguish these two layers leads to confusion:

• Why P2SH’s scriptPubKey has no OP_CHECKSIG




• Why SegWit moves scripts into the witness




• Why P2WSH and Taproot require revealing full scripts




• Why Taproot must reconstruct the tweaked key




• Why key-path spend is “scriptless”

With the correct architecture, everything clicks:

Commit–reveal is the philosophy.Dual-layer is the mechanism.

P2PKH only follows the philosophy. P2SH / P2WSH / Taproot script-path implement both.

5. The Unified Evolution

P2PK     → commit(pubkey)

P2PKH    → commit(hash(pubkey))

P2SH     → commit(hash(script))

P2WSH    → commit(sha256(script))

Taproot  → commit(internal_key + tweak(merkle_root))

Commitments grow more abstract. Privacy improves. Scripts expose less and less.

But the core remains unchanged:

Commit → Reveal → Execute

This is the true architecture of Bitcoin programmability.

By .

on July 3, 2026.