Introduction to V3 Custody
V3 Custody is an MPC platform for digital asset custody: key shares instead of private keys, policy checks before signing, and double-entry accounting behind every balance.
What is V3 Custody
V3 Custody is infrastructure for storing and moving digital assets without handing your keys to anyone, including us.
A complete private key never exists. Every outgoing transaction is checked against your organization's rules before a signature is created. Every movement of funds is recorded in an immutable double-entry ledger. You manage everything through the REST API, the web console, or approvals from your phone.
Three core principles
A key is a set of shares, not a file. Signing uses threshold ECDSA: each node holds its own key share, and the signature is produced jointly, so no single node, whether run by an operator or compromised by an attacker, ever sees the whole key. The complete key does not exist at any point in its lifecycle: not at creation, not during signing, and not during recovery.
Rules are configuration, not code. The Policy Engine evaluates every request before any key share is touched. Policies match on selectors (amount, asset, network, recipient address, wallet segment, initiator) and return one of three outcomes: allow, queue (held for approval), or block. Because the check happens before signing, a blocked transaction never has to be rolled back or revoked: it simply never reaches the blockchain.
Balances are computed, not stored. Every operation writes a balanced pair of debit and credit entries that are never edited or deleted. A balance is the result of those entries, so answering "why is this the number here" takes a query, not an investigation.
Vault: an address tree built on your schema
A Vault is a derivation scheme you design yourself rather than receive ready-made. You define the segments (network, purpose, asset, client index, stage) and their order, and the Vault turns them into deterministic derivation paths. Segments are either static, fixed for the entire Vault, or dynamic, creating a new branch per client, per request, or per deposit.
In practice, the address tree becomes your accounting model. The path shows what an address was created for, and the Policy Engine writes rules against the same segments instead of lists of opaque addresses.
Transaction lifecycle
Request
A transfer is created through the API, the web console, or the mobile app.
Policy check
The Policy Engine returns allow, queue, or block, along with the reason and the list of policies that matched.
Approval
Queued transactions wait for the approvers the policy requires. An approver sees the amount, the recipient, and the stated reason before signing off.
Signing
Only at this step do the MPC nodes jointly produce a signature. Key shares stay where they are.
Broadcast
The signed transaction is sent to the blockchain. The fee is sponsored by Gas Station, so the sending address doesn't need a native balance.
Ledger entry
The movement is recorded in the ledger as a pair of balanced entries with an idempotency key, so a retried request never doubles the amount.
Gas is no longer your problem
A freshly created address usually can't send a single cent until it receives TRX, ETH, or BNB. V3 Custody removes this step: you top up one Gas Station balance, in the native coin or plain USDT, and every address you create works from the first second.
Gas Station serves millions of addresses, not just yours, so fee sponsorship leaves no on-chain trail linking your addresses to each other. There is no shared funding wallet upstream for anyone to trace.
Who it's for
Teams that manage many addresses and need to explain every movement: exchanges and OTC desks, payment providers, services that assign a separate address to each user, and treasury departments that report to auditors.
Getting started
Quickstart
Spin up an instance and make your first API call.
Authentication
API keys, sessions, and approval authorization.
API Reference
All endpoints, parameters, and response formats.
Errors
Error codes and how to handle each one.
Not a developer? The Help Center covers everyday tasks: how to get access to a wallet, how to set up a custodial account, and what to check if a transaction won't sign.