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Domain Separation

Before an object is input to some cryptographic function, it is prepended with a multi-character domain-separating prefix.

All domain separators must be “prefix-free” (that is, they must not be concatenated).

The list below specifies each prefix:

  • For cryptographic primitives:

    • OT1 and OT2: The first and second layers of keys used for ephemeral signatures.
    • MA: An internal node in a Merkle tree.
    • MB: A bottom leaf in a vector commitment.
    • KP: Is a public key used by the Merkle Signature Scheme
    • spc: A coin used as part of the state proofs construction.
    • spp: Participant’s information (state proof public key and weight) used for state proofs.
    • sps: A signature from a specific participant used for state proofs.

  • In the Algorand Ledger:

    • BH: A Block Header.
    • BR: A Balance Record.
    • GE: A Genesis configuration.
    • spm: A State Proof message.
    • STIB: A SignedTxnInBlock that appears as part of the leaf in the Merkle tree of transactions.
    • TL: A leaf in the Merkle tree of transactions.
    • TX: A Transaction.
    • SpecialAddr: A prefix used to generate designated addresses for specific functions, such as sending state proof transactions.

  • In the Algorand Byzantine Fault Tolerance protocol:

    • AS: An Agreement Selector, which is also a VRF input.
    • CR: A Credential.
    • SD: A Seed.
    • PL: A Payload.
    • PS: A Proposer Seed.
    • VO: A Vote.

  • In other places:

    • arc: ARCs-related hashes https://github.com/algorandfoundation/ARCs. The prefix for ARC-XXXX should start with arcXXXX (where XXXX is the 0-padded number of the ARC). For example, ARC-0003 can use any prefix starting with arc0003.
    • MX: An arbitrary message used to prove ownership of a cryptographic secret.
    • NPR: A message that proves a peer’s stake in an Algorand networking implementation.
    • TE: An arbitrary message reserved for testing purposes.
    • Program: A TEAL bytecode program.
    • ProgData: Data that is signed within TEAL bytecode programs.

Auctions are deprecated; however, their prefixes are still reserved in code:

  • aB: A Bid.
  • aD: A Deposit.
  • aO: An Outcome.
  • aP: Auction parameters.
  • aS: A Settlement.