TYPE 0x0204 · HASH FAMILY

HASH_GUARDED

Raw SHA-256 preimage verification. SATISFIED when SHA256(preimage) equals the committed hash. Non-invertible and fail-closed.

Hash Non-Invertible

Ladder Diagram

Fields

Field	Data Type	Size	Side	Description
committed_hash	HASH256	32 B	Conditions	SHA-256 hash that the preimage must match
preimage	PREIMAGE	32 B	Witness	Data whose SHA-256 must equal committed_hash

Wire Format Breakdown

Conditions side (in scriptPubKey):

0x3D HASH256 · 32B = 33 bytes (micro-header)

Witness side (in input witness):

0x3D PREIMAGE · 32B = 33 bytes (micro-header)

Total (conditions + witness) ~66 bytes

Evaluation Logic

1. Require 1 HASH256 field + 1 PREIMAGE. Any missing → ERROR

2. Compute SHA256(PREIMAGE)

3. Compare result to committed_hash. If match → SATISFIED

4. Mismatch → UNSATISFIED

Return Values

Condition	Result
Missing HASH256 field	ERROR
Missing PREIMAGE field	ERROR
SHA256(preimage) does not match committed_hash	UNSATISFIED
SHA256(preimage) matches committed_hash	SATISFIED

JSON Wire Format

Conditions (scriptPubKey)

{
  "type": "HASH_GUARDED",
  "inverted": false,
  "fields": [
    { "type": "HASH256", "hex": "a1b2c3...32 bytes (committed_hash)" }
  ]
}

Witness (input)

{
  "type": "HASH_GUARDED",
  "inverted": false,
  "fields": [
    { "type": "PREIMAGE", "hex": "deadbeef...exactly 32 bytes" }
  ]
}

Use Cases

Standalone Hash Lock

Standalone hash lock. Provides raw SHA-256 preimage verification without requiring a companion signature block. Non-invertible by design, preventing data embedding through failed verification + inversion.

Commitment Reveal

Commit a hash on-chain, then reveal the preimage later to unlock funds. Useful for oracle-based protocols, escrow release, and data attestation where a signature is not needed.

Cross-Chain Hash Lock

Hash-locked spending conditions for atomic swap protocols where the hash preimage is revealed on another chain. Combine with SIG or COSIGN for additional authorization requirements.

Anti-Spam Properties

HASH_GUARDED is non-invertible: the inverted flag is rejected at deserialization. This prevents an attacker from creating a block with a garbage hash, providing arbitrary preimage data, and inverting the result to SATISFIED. There is no way to embed arbitrary data through this block type.

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