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
HASH_GUARDED SHA-256(pre) → == committed_hash SHA256(preimage) == committed_hash
Fields
FieldData TypeSizeSideDescription
committed_hash HASH256 32 B Conditions SHA-256 hash that the preimage must match
preimage PREIMAGE var Witness Data whose SHA-256 must equal committed_hash. Length is unconstrained — the full byte run is consumed.
Wire Format Breakdown

Conditions side (committed in the rung leaf):

0x0204 0 1 HASH256 · 32B = 38 bytes

Witness side (in input witness):

0x0204 0 1 PREIMAGE · var ≈ 4 + 1 + len bytes
Total (conditions + witness) ≈ 43 + len bytes

The "inverted" byte is rejected at deserialization for HASH_GUARDED (non-invertible). PubkeyCountForBlock = 0.

Evaluation Logic
1. Locate the HASH256 and PREIMAGE fields in the merged conditions+witness block. If either is missing → ERROR
2. committed_hash must be exactly 32 B; otherwise → ERROR
3. Compute SHA256(PREIMAGE) using CSHA256. The PREIMAGE length is unconstrained — the full byte run is consumed.
4. memcmp the 32-byte result against committed_hash. Equal → SATISFIED; differs → UNSATISFIED
Return Values
ConditionResult
HASH256 or PREIMAGE field missingERROR
committed_hash not exactly 32 BERROR
SHA256(preimage) ≠ committed_hashUNSATISFIED
SHA256(preimage) = committed_hashSATISFIED
JSON Wire Format
Conditions (committed in the rung leaf)
{
  "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... (variable-length preimage)" }
  ]
}
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.

← TAGGED_HASH CTV →