Block Signatures

Finalized

Block signatures attest that a node validated a candidate block and authorizes it to be considered for acceptance. In v10+ the signature is accompanied by the signer’s PoCW eligibility solution for a recent reference block.

This page specifies only the on-wire structures used inside blocks and on the network. It does not prescribe implementation details.

Concepts

  • Signers must first obtain eligibility via a PoCW solution for a recent reference block.
  • For v10+, the RSA signature covers the digest sha3_512sq(blockChecksum || powSolution.solution). This binds the specific PoCW solution (nonce) to the signed block.
  • Signatures included in a block are encoded in a compact header form to conserve space. The RSA signature bytes are omitted and the signing public key may be replaced by its 64-byte hash. The full form (including RSA signature) is used with recent blocks.

Data Types

  • IxiVarInt / IxiVarUInt: variable-length integers.
  • IxiBytes: length-prefixed byte array.

Signature Structure (in Block Header, v10+)

When included in a block's Signatures section, each entry is encoded in a compact form to minimize header size. The RSA signature bytes are omitted, and the public key may be hashed.

FieldTypeNotes
signerIxiBytesSigner identifier. In compacted headers this is the address without checksum (or an address-derived identifier).
powSolutionIxiBytesEncoded PoCW solution (see below). May contain a hash of the signing public key instead of the full key in compacted form.

If the block is later compacted by a superblock, the entire signatures list can be replaced by:

  • compactedSignatureCount: IxiVarUInt
  • totalSignerDifficultyBits: IxiVarUInt (aggregate difficulty encoded in bits)

PoCW Solution (v10+)

Encodes the signer's eligibility proof parameters:

FieldTypeConstraintsDescription
blockNumIxiVarUIntReference block height used for the challenge.
solutionIxiBytes1-64 bytesNonce that satisfies the target difficulty for the challenge.
signingPubKeyIxiBytes<= 300 bytes (header may use 64-byte hash)Public key used to sign the block (or its hash in compacted form).

PoCW challenge hash (little-endian where applicable):

sha3_512sq( IxiVarUInt(blockNum) || blockChecksum(blockNum) || recipientAddressNoChecksum || hashOrBytes(signingPubKey) || solution )
  • blockChecksum(blockNum) is the checksum of the reference block at height blockNum.
  • recipientAddressNoChecksum is the binary address (without its 3-byte checksum) of the signer.
  • hashOrBytes(signingPubKey) equals sha3_512sq(signingPubKey) if the key is longer than 64 bytes, otherwise the raw bytes.
  • Difficulty is derived from this hash; aggregate difficulty may be compacted into bits for storage.

Signature Structure (network broadcast)

When signatures are broadcast as standalone messages, the full form is sent:

FieldTypeNotes
blockNumIxiVarUIntTarget block number being signed.
blockHashIxiBytesTarget block checksum.
signerIxiBytesSigner identifier (address or public key).
powSolutionIxiBytesFull PoCW solution with public key.
signatureIxiBytesRSA signature over `sha3_512sq(blockHash

Verification checklist (receiver)

For each received signature (header entry or broadcast message):

  1. Validate PoCW solution window and minimum difficulty per consensus parameters.
  2. Recompute the PoCW challenge hash from blockNum, reference blockChecksum(blockNum), signer address, signingPubKey (or its hash), and solution.
  3. Verify the RSA signature over sha3_512sq(blockHash || powSolution.solution) using the included signingPubKey (or the resolved public key).
  4. Ensure the signer is eligible and has not already signed the block (per-block uniqueness).

Notes:

  • Header-embedded entries omit the RSA signature and may carry a hashed signingPubKey; full verification requires fetching the broadcast form if not otherwise known.
  • In compacted blocks, totalSignerDifficultyBits preserves aggregate difficulty for historical accounting.

Addresses

Blocks