Dash Core

Dash Core Developer Documentation

Welcome to the Dash Core developer documentation. You'll find guides and documentation to help you start working with Dash Core as quickly as possible, as well as support if you get stuck. Let's jump right in!

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Dash Core's mixing feature provides a way to improve privacy by performing non-custodial CoinJoin. For additional details, reference this Official Documentation page.

The following video provides an overview with a good introduction to the details:

Wallet Preparation

The walletwallet - Software that stores private keys and monitors the block chain (sometimes as a client of a server that does the processing) to allow users to spend and receive duffs. completes two operations in this phase:

  1. Split value into inputs matching the CoinJoin denominationsdenominations - Denominations of Dash value, usually measured in fractions of a dash but sometimes measured in multiples of a duff. One dash equals 100,000,000 duffs. by sending transactionstransactions - A transaction spending satoshis. to itself

  2. Split value into inputsinputs - An input in a transaction which contains three fields: an outpoint, a signature script, and a sequence number. The outpoint references a previous output and the signature script allows spending it. to use for collateral by sending transactions to itself

Note: Both these operations incur the standard transaction feetransaction fee - The amount remaining when the value of all outputs in a transaction are subtracted from all inputs in a transaction; the fee is paid to the miner who includes that transaction in a block. like any other transaction

Creating Denominations

The CoinJoin denominations include a bit mapping to easily differentiate them. The dsa message and dsq message use this bit shifted integer instead of sending the actual denomination. The table below lists the bit, its associated integer value used in P2P messages, and the actual Dash value.

BitDenom. (Integer)Denomination (DASH)
0110.0001
1201.00001
2400.100001
3800.0100001
41600.00100001

Protocol version 70213 added a 5th denomination (0.001 DASH).

Example Testnet denomination creation transaction

Creating Collaterals

Collaterals are used to pay CoinJoin fees, but are kept separate from the denominations to maximize privacy. Since protocol version 70213, the minimum collateral fee is 1/10 of the smallest denomination for all sessions regardless of denomination. In Dash Core, collaterals are created with enough value to pay 4 collateral fees (4 x 0.001 DASH). (Dash Core Reference)

In protocol version 70208, collateral inputs can be anything from 2x the minimum collateral amount to the maximum collateral amount (currently defined as 4x the minimum collateral). In protocol versions > 70208, Dash Core can use any inputinput - An input in a transaction which contains three fields: an outpoint, a signature script, and a sequence number. The outpoint references a previous output and the signature script allows spending it. from 1x the minimum collateral amount to the maximum collateral amount.

Example Testnet collateral creation transaction

Example Testnet collateral payment transaction

CoinJoin Processing

This phase involves exchanging a sequence of messages with a masternodemasternode - A computer that provides second-tier Dash functionality (InstantSend, PrivateSend, decentralized governance). Masternodes are incentivized by receiving part of the block reward, but must hold 1000 Dash as collateral to prevent sybil attacks. so it can construct a denominate transaction with inputs from the clients in its pool.

Data Flow

ClientsDirectionMasternodeDescription
0Client determines whether to join an existing pool or create a new one
1dsa messageClient asks to join pool or have the masternode create a new one
2dssu messageMasternode provides a pool status update (Typical - State: POOL_STATE_QUEUE, Message: MSG_NOERR)
3dsq messageMasternode notifies clients when it is ready to receive inputs
4dsi messageUpon receiving a dsq message with the Ready bit set, clients each provide a list of their inputs (unsigned), collateral, and a list of outputs where funds should be sent
5dssu messageMasternode provides a pool status update (typical - State: POOL_STATE_ACCEPTING_ENTRIES, Message: MSG_ENTRIES_ADDED)
6dsf messageMasternode sends the final transaction containing all clients inputs (unsigned) and all client outputs to each client for verification
7dssu messageMasternode provides a pool status update (Typical - State: POOL_STATE_SIGNING, Message: MSG_NOERR)
8dss messageAfter verifying the final transaction, clients each sign their own inputs and send them back
9dsc messageMasternode verifies the signed inputs, creates a dstx message to broadcast the transaction, and notifies clients that the denominate transaction is complete (Typical - Message: MSG_SUCCESS)
10inv messageMasternode broadcasts a dstx inventory message
11getdata message (dstx)(Optional)

Additional notes

Step 0 - Pool Selection

  • Existing pool information is derived from the Queue messages seen by the client
  • Dash Core attempts to join an existing pool and only requests creation of a new one if that fails, although this is not a requirement that alternative implementations would be required to follow

Step 1 - Pool Request

  • The dsa message contains a collateral transaction
    • This transaction uses a collateral inputinput - An input in a transaction which contains three fields: an outpoint, a signature script, and a sequence number. The outpoint references a previous output and the signature script allows spending it. created in the Wallet Preparation phase
    • The collateral is a signed transactiontransaction - A transaction spending satoshis. that pays the collateral back to a client addressaddress - A 20-byte hash formatted using base58check to produce either a P2PKH or P2SH Dash address. Currently the most common way users exchange payment information. minus a fee of 0.001 DASH

Step 3 - Queue

  • A masternode broadcasts dsq messages when it starts a new queue. These message are relayed by all peerspeers - A computer that connects to the Dash network..
  • As of protocol version 70214, sessions have a variable number of participants defined by the range nPoolMinParticipants (3) to nPoolMaxParticipants (5). Prior protocol version sessions always contained exactly 3 participants. Spork 22 introduced in Dash Core 0.16.0 expanded the maximum number of participants to 20 and also reduced the minimum number of participants to 2 for testnet/devnet/regtest networks. The spork was removed in Dash Core 0.17.0 which made the change permanent.
  • The masternode sends a dsq message with the ready bit set once it has received valid dsa messages from either:
    1. The maximum number of clients (20)
    2. Greater than the minimum number of clients (3) and the timeout has been reached (30 seconds)

🚧

Clients must respond to the Queue ready within 30 seconds or risk forfeiting the collateral they provided in the dsa message (Step 1) (Dash Core Reference)

Step 4 - Inputs

  • The collateral transaction can be the same in the dsi message as the one in the dsa message (Step 1) as long as it has not been spent
  • Each client can provide up to 9 (COINJOIN_ENTRY_MAX_SIZE) inputs (and an equal number of outputs) to be used (Dash Core Reference)
  • This is the only message in the process that contains enough information to link a wallet's CoinJoin inputs with its outputs
    • This message is sent directly between a client and the masternode processing the session (not relayed across the Dash network) so no other clients see it

Step 6 - Final Transaction (unsigned)

  • Once the masternode has received valid dsi messages from all clients, it creates the final transaction and sends a dsf message
    • Inputs/outputs are ordered deterministically as defined by BIP-69 to avoid leaking any data (Dash Core Reference)
    • Clients must sign their inputs to the Final Transaction within 15 seconds or risk forfeiting the collateral they provided in the dsi message (Step 4) (Dash Core Reference)

Step 10 - Final Transaction broadcast

  • Prior to protocol version 70213, masternodes could only send a single un-mined dstx message at a time. As of protocol version 70213, up to 5 (MASTERNODE_MAX_MIXING_TXES) un-mined dstx messages per masternode are allowed. (Dash Core Reference)

General

With the exception of the dsq message and the dstx message (which need to be public and do not expose any private information), all CoinJoin P2P messages are sent directly between the masternode processing the transaction and the relevant client(s).

Fees

Processing Fees

  • If processing completes successfully, Dash Core charges the collateral randomly in 1/10 denominate transactions to pay miners (Dash Core Reference)
  • Clients that abuse the system by failing to respond to dsq messages or dsf messages within the timeout periods may forfeit their collateral. Dash Core charges the abuse fee in 2/3 cases (Dash Core Reference)

Sending Fees

To maintain privacy when using CoinJoin funds, transactions must fully spend all inputs to a single output (with the remainder becoming the fee - i.e. no change outputchange output - An output in a transaction which returns duffs to the spender, thus preventing too much of the input value from going to transaction fees.). This can result in large fees depending on the value being sent.

For example, an extreme case is sending the minimum non-dust value (546 duffs). This results in an extremely large transaction fee because the minimum denomination (0.00100001 DASH or 100,001 duffs) must be fully spent with no change. This results in a fee of 0.00999464 DASH and a sent value of only 0.00000546 DASH as shown by the calculation below.

100001 duffs (smallest CoinJoin denomination) - 546 duffs (value to send) = 99455 duffs (fee)

Updated 3 months ago



CoinJoin


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