Documentation

Introduction to P2WSH (Pay-To-Witness-Script-Hash)

Overview

P2WSH (Pay-to-Witness-Script-Hash) is a native Segregated Witness address format introduced in BIP141 that combines the flexibility of P2SH with the benefits of SegWit. These addresses begin with bc1q on mainnet (similar to P2WPKH but longer) and enable complex spending conditions with reduced fees, increased script size limits, and transaction malleability protection.

How It Works

P2WSH addresses are derived from a witness script through the following process:

The following diagram shows the anatomy of a P2WSH address:
P2WSH Address Anatomy Script Hash Generation Witness Script Variable length (e.g. multisig) SHA-256 Script Hash 32 bytes Bech32 Encoding HRP "bc" + Version 0x00 + Script Hash 32 bytes Witness Program (33 bytes) Bech32 Encode with checksum (6 chars) HRP "bc" 1 Version "q" (0) Script Hash (Bech32 encoded) 32 bytes → 52 chars Checksum 6 chars 62 characters total (starts with bc1q) P2WSH Address bc1qrp33g0q5c5txsp9arysrx4k6zdkfs4nce4xj0gdcccefvpysxf3qccfmv3
  1. Create a witness script defining the spending conditions (e.g., multisig, timelock, or custom logic).
  2. Apply SHA-256 hashing to the witness script, producing a 256-bit hash (32 bytes).
  3. Create a witness program by combining witness version 0 with the 32-byte script hash.
  4. Encode the witness program using Bech32 encoding with the appropriate human-readable prefix.

P2WSH vs P2SH

Unlike P2SH which uses HASH160 (SHA-256 + RIPEMD-160) to produce a 20-byte hash, P2WSH uses only SHA-256 to produce a 32-byte hash. This provides stronger collision resistance (256-bit vs 160-bit) and allows for more secure complex scripts.

Feature P2SH P2WSH
Hash Algorithm HASH160 (SHA-256 + RIPEMD-160) SHA-256 only
Hash Size 20 bytes (160-bit) 32 bytes (256-bit)
Script Size Limit 520 bytes 10,000 bytes
Encoding Base58Check Bech32
Address Prefix (Mainnet) 3 bc1q
Script/Signature Location ScriptSig Witness data
SegWit Fee Discount No Yes (witness data at 1/4 weight)
Malleability Protection No Yes

Witness Scripts

The witness script defines the actual spending conditions, similar to a P2SH redeem script.

Common witness script types include:

Multisig (M-of-N)

Requires M signatures from N possible public keys.

The following example shows a 2 of 3 signatures script:
plaintext
OP_2
<pubkey1>
<pubkey2>
<pubkey3>
OP_3
OP_CHECKMULTISIG

Timelock

Funds can only be spent after a specific time or block height.

The following example shows a specific time or block height script:
plaintext
<expiry_time>
OP_CHECKLOCKTIMEVERIFY
OP_DROP
<pubkey>
OP_CHECKSIG

Complex Conditional Scripts

P2WSH's larger script limit enables more sophisticated conditions.

The following example shows a more sophisticated script:
plaintext
OP_IF
    OP_2
    <pubkey1>
    <pubkey2>
    <pubkey3>
    OP_3
    OP_CHECKMULTISIG
OP_ELSE
    <timeout>
    OP_CHECKSEQUENCEVERIFY
    OP_DROP
    <recovery_pubkey>
    OP_CHECKSIG
OP_ENDIF

Security Considerations

P2WSH provides enhanced security compared to P2SH through its use of a full 256-bit SHA-256 hash. This offers significantly stronger collision resistance—finding two different scripts that produce the same hash is computationally infeasible.

The spending conditions remain hidden until the funds are spent, similar to P2SH. However, once spent, the full witness script is revealed on the blockchain. For maximum privacy, consider using Taproot (P2TR) which can hide unused script branches permanently.

P2WSH inherits SegWit's transaction malleability fix. Since signatures are stored in the witness data (which is not included in the transaction ID calculation), third parties cannot modify transaction IDs. This is crucial for protocols that depend on unconfirmed transaction chains.

The increased script size limit (10,000 bytes vs 520 bytes for P2SH) enables more complex spending conditions but also requires careful script design to avoid excessive transaction fees.

Address Format

P2WSH addresses use Bech32 encoding with a 32-byte witness program:

  • Mainnet — Addresses start with bc1q .
  • Testnet — Addresses start with tb1q.
  • Regtest — Addresses start with bcrt1q.
On this page