Terms used across this documentation, defined once.
Chain and consensus
Anchor block. A block whose header carries a post-quantum certificate over its parent, and whose block hash covers a commitment to that certificate. Every 128th block on a grid offset from block 17,225,968.
Certificate. The set of validator seals attached to an anchor header, encoded and committed to by a 32-byte digest in vanityData.
Deterministic finality. A committed block does not reorganise. One confirmation is final. This is a property of QBFT, not a probabilistic assumption.
f. The number of faulty validators the consensus tolerates. On chain 2800, f = 2 with nine validators.
Quorum. The number of validators that must agree for a block to commit: six of nine.
QBFT. The Byzantine fault tolerant consensus engine from Hyperledger Besu that chain 2800 runs.
Seal. One validator's signature. A classical seal is secp256k1; a post-quantum seal is Falcon-512 or SLH-DSA-SHA2-128s.
extraData. The header field carrying QBFT's consensus data. On chain 2800 it has an AERE sixth element, and element 0, vanityData, carries the anchor digest.
Cryptography
Falcon-512, Falcon-1024. Lattice-based post-quantum signature schemes from the NIST process. Signatures are compressed and therefore variable length.
ML-DSA-44. FIPS 204, the standardised lattice-based signature scheme, formerly Dilithium.
SLH-DSA-SHA2-128s. FIPS 205, the standardised hash-based signature scheme, formerly SPHINCS+. Large and slow, and dependent on nothing but the hash function.
SHAKE256. FIPS 202 extendable-output hash function.
Hybrid certificate. A certificate carrying seals from two different signature families at once, so that a break in one family does not break the certificate. Live from block 17,047,600.
HNDL, harvest now decrypt later. A threat to encrypted data, not to signatures. It does not apply to a blockchain signature, which is public the moment it is made. See Threat model.
Long-range attack. Rewriting old history using validator keys recovered later. This is the threat the anchor addresses.
Positive control. A check, run in the same execution as a measurement, that a thing known to be present is found. Without it, a zero from a broken tool is indistinguishable from a zero that was earned. This term appears throughout our documentation because it is the difference between a measurement and a guess.
Operations
Anchor interval. How often an anchor block occurs. 32 until block 17,225,968, then 128.
Enforcement height. The block number at which a consensus rule begins to be required.
Follower. A node that follows the chain without producing blocks.
Registry. The list of validator post-quantum public keys, indexed, against which certificate seals are verified. Its hash is committed in the genesis config.
State window. The number of recent blocks for which an endpoint keeps state. 512 on the public RPC, beyond which some reads return a false zero rather than an error.