> ## Documentation Index
> Fetch the complete documentation index at: https://docs.quantumapi.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Glossary

> Terms and concepts used across Quantum Chain and Qustody.

## A

**Address** — A 20-byte identifier for a Quantum Chain account, displayed as `0x` plus 40 hex characters. Derived from `Keccak-256(publicKey)[0:20]`.

**API key** — A bearer token issued by Qustody that authenticates a service-to-service caller. Created via `POST /v1/credentials`, rotated via `POST /v1/credentials/rotate`.

**Approval** — A signed acknowledgement from a user holding the `approver` role that a transaction may proceed. Required when a `REQUIRE_APPROVAL` policy rule matches.

**Audit log** — A tamper-evident, hash-chained record of every state-changing API call. Verified via `GET /v1/audit/verify`.

**AML screening** — Anti-money-laundering check performed against the destination address (and optionally the sender) before broadcast. Provided by Chainalysis or Shufti Pro.

## B

**Bootnode** — A discovery v4 node that helps new geth instances find peers. Run via `build/bin/bootnode`.

**Broadcast** — Submitting a signed transaction to the Quantum Chain network via `eth_sendRawTransaction`. Returns a transaction hash.

## C

**Callback signing mode** — The signer integration mode where Qustody exposes a signing payload and waits for the signer to POST a signature back. Set with `CUSTODY_SIGNER_TYPE=callback`.

**Chain ID** — The network identifier embedded in every signed transaction. `20803` for Quantum Chain mainnet.

**Circuit breaker** — A reliability primitive in Qustody that opens after repeated failures to a downstream (signer, AML provider, RPC node), preventing cascade failures.

**Clique** — The Proof-of-Authority consensus algorithm used by Quantum Chain. A fixed sealer set takes turns producing blocks.

**Confirmation** — A block built on top of a transaction's block. Qustody waits `CUSTODY_CONFIRMATION_DEPTH` confirmations (default 12) before marking a transaction `CONFIRMED`.

**Custody platform** — A system that manages keys, policies, approvals, and audit on behalf of an organization. Qustody is the reference implementation for Quantum Chain.

## D

**Devnet** — A local development network. Typically a single Clique sealer with `period=5`.

**Digest** — The 32-byte `Keccak-256` hash that the post-quantum signer signs.

## E

**Epoch** — The interval at which a Clique chain finalizes its sealer set. `30000` blocks on Quantum Chain mainnet.

**EVM** — Ethereum Virtual Machine. Quantum Chain runs the **QVM**, which inherits EVM bytecode, opcodes, and gas accounting but removes the `ecrecover` precompile and adds a post-quantum verification precompile at `0x0b`. See [QVM vs EVM](/quantum-chain/qvm-vs-evm).

**External signer** — A separate process or service that holds private keys and produces signatures on demand. Required for production Qustody deployments.

## G

**geth** — The Quantum Chain reference client, a fork of go-ethereum. Built with `make geth`.

**gRPC signing mode** — Qustody calls the signer over gRPC with mTLS. Set with `CUSTODY_SIGNER_TYPE=grpc`. Recommended for production.

## I

**Idempotency key** — A UUID provided by the caller in the `Idempotency-Key` header. Within 24 hours, repeating a request with the same key returns the original response without re-executing.

## K

**Keystore** — A JSON file containing an encrypted post-quantum private key (AES-128-CTR + PBKDF2). The file format matches the standard Web3 Secret Storage definition.

## M

**Mempool** — The pool of pending transactions held by each geth node before they're sealed into a block.

**Mnemonic** — A 12-word BIP-39 phrase that deterministically regenerates a post-quantum keypair. Generated by `keygenerator`; never stored on disk.

## N

**Nonce** — The sequential count of transactions sent from a given address. Quantum Chain (like Ethereum) requires nonces to be sequential.

**Non-custodial** — The property that the platform never holds the user's private keys. Qustody is non-custodial — keys live in the external signer.

## P

**Policy** — A rule set attached to a vault that constrains which transactions may proceed. Supported rules: `MAX_AMOUNT`, `WHITELIST_ADDRESS`, `BLACKLIST_ADDRESS`, `REQUIRE_APPROVAL`, `TIME_WINDOW`, `DAILY_LIMIT`.

**Post-quantum signature** — A signature produced by a cryptographic scheme believed to be secure against quantum-capable adversaries. Used by Quantum Chain in place of ECDSA.

**Public key** — The verification key paired with a post-quantum private key. Registered with Qustody when a wallet is created.

## Q

**Quantum (QUANTUM)** — The native currency of Quantum Chain. Quantum is to Quantum Chain what ETH is to Ethereum: it pays for gas and is the base unit of value transfer. Referenced in the Qustody API by `asset_id: "QUANTUM"`. The smallest denomination is `wei` (1 QUANTUM = 10^18 wei).

**QRC token standard** — A family of Quantum Chain token standards (QRC-20, QRC-721, QRC-1155, QRC-1400, QRC-3643, QRC-4626, QRC-3525) that mirror the operational shape of widely-used Ethereum-style standards while running on the QVM and being authorized with post-quantum signatures. See [Token standards](/reference/token-standards).

**QVM** — Quantum Virtual Machine. The execution layer of Quantum Chain. EVM-compatible at the bytecode, opcode, and gas-accounting level, but the cryptographic primitives differ: `ecrecover` is removed and a post-quantum verification precompile is added at `0x0b`. See [QVM vs EVM](/quantum-chain/qvm-vs-evm).

**Qustody** — The reference custody platform for Quantum Chain. Multi-tenant, non-custodial, policy-driven.

## R

**RBAC** — Role-Based Access Control. Qustody ships with five system roles (`admin`, `operator`, `viewer`, `approver`, `compliance_officer`) and supports custom roles.

**Reorg** — A reorganization of the canonical chain when a longer fork is observed. Bounded in Clique by sealer-out-of-turn rules.

**Remote signing mode** — Qustody calls the signer over HTTPS. Set with `CUSTODY_SIGNER_TYPE=remote`.

## S

**Sealer** — A validator in the Clique sealer set. Sealers take turns proposing blocks every `period` seconds.

**Signing payload** — The data a signer must sign for a Qustody transaction: the transaction's Keccak-256 digest, plus metadata (nonce, chain ID).

**Snap sync** — The default geth sync mode. Downloads recent block headers and a state snapshot.

## T

**Tenant** — The top-level isolation boundary in Qustody. All resources (vaults, wallets, transactions, users, policies) are scoped to a tenant.

**Token (Qustody)** — A Qustody-tracked record representing a deployed or to-be-deployed QRC token contract on Quantum Chain. Has an `id`, `standard`, `symbol`, `decimals`, `contractAddress`, `status`, `adminVaultAccountId`, and `approvalPolicyId`. See [Token management](/qustody/token-management/overview).

**Token allowlist** — An on-chain or off-chain list of addresses permitted to hold or transfer a permissioned QRC token. Maintained per token through the `/v1/tokens/{tokenId}/allowlist` endpoints.

**Token configuration** — A draft of a token's parameters stored in Qustody before deployment: standard, symbol, decimals, supply policy, admin vault, approval policy.

**Token operation** — A single privileged action against a Qustody-managed token (`DEPLOY_TOKEN`, `MINT`, `BURN`, `TRANSFER`, `GRANT_ROLE`, `REVOKE_ROLE`, `PAUSE`, `UNPAUSE`, `FREEZE`, `UNFREEZE`, `UPDATE_COMPLIANCE`). Each operation flows through the existing transaction state machine and produces an audit-log entry.

**Token template** — A pre-validated contract template that Qustody can instantiate for a chosen QRC standard. Listed via `GET /v1/token-templates`.

**Transaction state machine** — The 14-state lifecycle a Qustody transaction moves through. See [State machine](/concepts/state-machine).

**Travel rule** — A regulatory requirement to share originator and beneficiary information with counter-party VASPs above a threshold. Supported by Qustody's compliance endpoints.

## V

**Vault** — A logical grouping of wallets within a tenant. Policies attach to vaults.

**Validator** — Synonym for sealer; a Quantum Chain node authorized to produce blocks.

## W

**Wallet** — A Qustody record representing a Quantum Chain address and its registered post-quantum public key. Created with `POST /v1/wallets`.

**Webhook** — An HTTPS endpoint Qustody POSTs events to. Each delivery is signed with HMAC-SHA256 using the per-endpoint secret.