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[Content] - Update PrivateSend collateral info (#62 )

- Change for protocol >70208 to provide more flexibility
Closes #48

2018-04-18 17:21:03 -04:00

30 KiB

Raw Blame History

{% comment %} This file is licensed under the MIT License (MIT) available on http://opensource.org/licenses/MIT. {% endcomment %} {% assign filename="_includes/devdoc/guide_dash_features.md" %}

Dash Features

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Dash aims to be the most user-friendly and scalable payments-focused cryptocurrency in the world. The Dash network features instant transaction confirmation, double spend protection, anonymity equal to that of physical cash, a self-governing, self-funding model driven by incentivized full nodes and a clear roadmap for on-chain scaling to up to 400MB blocks using custom-developed open source hardware.

While Dash is based on Bitcoin and compatible with many key components of the Bitcoin ecosystem, its two-tier network structure offers significant improvements in transaction speed, anonymity and governance. This section of the documentation describes these key features that set Dash apart in the blockchain economy.

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InstantSend

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Dash Core's InstantSend feature provides a way to lock transaction inputs and enable secure, instantaneous transactions.

The following video provides an overview with a good introduction to the details including the InstantSend vulnerability that was fixed in Dash Core 0.12.2. Some specific points in the video are listed here for quick reference:

2:00 - InstantSend restrictions
5:00 - Masternode quorum creation
6:00 - Input locking
7:45 - Quorum score calculation / Requirement for block confirmations
9:00 - Description of Dash Core pre-0.12.2 InstantSend vulnerability
13:00 - Description of vulnerability fix / Post Dash Core 0.12.2 operation

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InstantSend Data Flow

Once a sufficient number of votes approve the transaction lock, the InstantSend transaction is approved and shows 5 confirmations (DEFAULT_INSTANTSEND_DEPTH).

NOTE: The 5 "pseudo-confirmations" are shown to convey confidence that the transaction is secure from double-spending and DO NOT indicate the transaction has already been confirmed to a block depth of 5 in the blockchain.

If an InstantSend transaction is a valid transaction but does not receive a transaction lock, it reverts to being a standard transaction.

There are a number of limitations on InstantSend transactions:

The lock request will timeout 15 seconds after the first vote is seen (INSTANTSEND_LOCK_TIMEOUT_SECONDS)
The lock request will fail if it has not been locked after 60 seconds (INSTANTSEND_FAILED_TIMEOUT_SECONDS)
A minimum fee (0.0001 Dash) is required since the transaction involves the masternodes in addition to miners. This fee was most recently decreased by DIP-0001.
To be used in an InstantSend transaction, an input must have at least the number confirmations (block depth) indicated by the table below

Network	Confirmations Required
Mainnet	6 Blocks
Testnet	2 Blocks
Regtest	2 Blocks
Devnet	2 Blocks

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PrivateSend

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Dash Core's PrivateSend feature provides a way to improve privacy by performing coin-mixing without relinquishing custodial access. For additional details, reference this Official Documentation PrivateSend page.

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

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PrivateSend Wallet Preparation

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The wallet completes two operations in this phase:

Split value into inputs matching the PrivateSend denominations by sending transactions to itself
Split value into inputs to use for collateral by sending transactions to itself

Note: Both these operations incur standard transaction fees like any other transaction

Creating Denominations

The PrivateSend 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.

| Bit | Denom. (Integer) | Denomination (DASH) | | 0 | 1 | 10.0001 | | 1 | 2 | 01.00001 | | 2 | 4 | 00.100001 | | 3 | 8 | 00.0100001 |

The denominations are structured to allow converting between denominations directly without requiring additional inputs or creating change (for example, 1 x 10.0001 = 10 x 1.00001, 1 x 0.100001 = 10 x 0.0100001, etc.).

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Example Testnet denomination creation transaction

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Creating Collaterals

PrivateSend collaterals are used to pay mixing fees, but are kept separate from the denominations to maximize privacy. The minimum collateral fee is 0.001 DASH for all mixing 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 input from 1x the minimum collateral amount to the maximum collateral amount.

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Example Testnet collateral creation transaction

Example Testnet collateral payment transaction

PrivateSend Mixing

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The mixing phase involves exchanging a sequence of messages with a masternode so it can construct a mixing transaction with inputs from the clients in its mixing pool.

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PrivateSend Data Flow

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

Additional notes

Step 0 - Pool Selection

Existing mixing pool information is derived from the Queue messages seen by the client
Dash Core attempts to join an existing mixing pool 2/3 of the time although this is not a requirement that alternative implementations would be required to follow (Dash Core Reference)

Step 1 - Pool Request

The dsa message contains a collateral transaction
- This transaction uses a collateral input created in the Wallet Preparation phase
- The collateral is a signed transaction that pays the collateral back to a client address 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 peers.
Once the masternode has received valid dsa messages from 3 clients (nPoolMaxTransactions), it sends a dsq message with the ready bit set (Dash Core Reference)
- 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 (PRIVATESEND_ENTRY_MAX_SIZE) inputs (and an equal number of outputs) to be mixed (Dash Core Reference)
This is the only message in the PrivateSend process that contains enough information to link a wallet's PrivateSend inputs with its outputs
- This message is sent directly between a client and the mixing masternode (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)

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 PrivateSend P2P messages are sent directly between the mixing masternode and relevant client(s).

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PrivateSend Fees

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Mixing Fees

If mixing completes successfully, Dash Core charges the collateral randomly in 1/10 mixing transactions to pay miners (Dash Core Reference)
Clients that abuse the mixing 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 PrivateSend, PrivateSend transactions must fully spend all inputs to a single output (with the remainder becoming the fee - i.e. no change outputs). 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) via PrivateSend. This results in an extremely large transaction fee because the minimum PrivateSend denomination (0.0100001 DASH or 1,000,010 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.

1000010 duffs (smallest PrivateSend denomination) - 546 duffs (value to send) = 999464 duffs (fee)

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Example Testnet PrivateSend transaction spending 546 duffs

Masternode Payment

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Masternode payment uses a verifiable process to determine which masternode is paid in each block. When a new block is processed, a quorum of MNPAYMENTS_SIGNATURES_TOTAL (10) masternodes vote on the next masternode payee. The quorum is calculated deterministically based on the distance between masternode's hash and the block's proof of work.

Each member of the quorum issues a 'mnw' message that is relayed to the network. The payee is selected from a subset of masternodes made up of 10% of eligible nodes that have been waiting the longest since their last payment. The winner is then determined based on a number of parameters including the distance between the its hash and the block's proof of work. For additional detail, reference this Official Documentation Payment Logic page.

Nodes receiving a mnw message verify the validity of the message before relaying it to their peers. If the message is invalid, the sending node may be treated as misbehaving and have its ban score increased.

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Masternode Sync

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Dash Core performs full masternode synchronization as required. There are several conditions that initiate a start/restart the sync process:

Initial startup of Dash Core
More than 60 minutes have passed since the last activation
A failure occurred during the last sync attempt (after a 1 minute cooldown before sync restarts)
Issuing a mnsync reset RPC command

Initial Masternode Sync

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This diagram shows the order in which P2P messages are sent to perform masternode synchronization initially after startup.

The following table details the data flow of P2P messages exchanged during initial masternode synchronization.

Masternode Sync Status

There are several status values used to track masternode synchronization. They are used in both ssc messages and the mnsync RPC.

Ongoing Masternode Sync

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Once a masternode completes an initial full sync, continuing synchronization is maintained by the exchange of P2P messages with other nodes. This diagram shows an overview of the messages exchanged to keep the masternode list, masternode payments, and governance objects synchronized between masternodes.

Recurring Ping

Each masternode issues a ping (mnp message) periodically to notify the network that it is still online. Masternodes that do not issue a ping for 3 hours will be put into the MASTERNODE_NEW_START_REQUIRED state and will need to issue a masternode announce (mnb message).

Masternode List

After the initial masternode list has been received, it is kept current by a combination of the periodic mnp messages received from other masternodes, the mnb messages sent by masternodes as they come online, and mnv messages to verify that other masternodes are valid.

Also, dseg messages can be sent to request masternode info when messages are received that have been signed by an unrecognized masternode (most masternode/governance messages include a vin value that can be used to verify the masternode's unspent 1000 Dash).

Unsynchronized peers may send a dseg message to request the entire masternode list.

Masternode Payment

After the initial masternode payment synchronization, payment information is kept current via the mnw messages relayed on the network. Unsynchronized peers may send a mnget message to request masternode payment sync.

Governance

After the initial governance synchronization, governance information is kept current by the govobj messages and govobjvote messages relayed on the network. Unsynchronized peers may send govsync messages to request governance sync.

Masternode Sync Schedule

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The following tables detail the timing of various functions used to keep the masternodes in sync with each other. This information is derived from ThreadCheckPrivateSend in src/privatesend.cpp.

The following actions only run when the masternode sync is past MASTERNODE_SYNC_WAITING status.

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Governance

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Synchronization

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Dash Core synchronizes the governance system via the Masternode network as the last stage of the Masternode sync process (following the sync of sporks, the Masternode list, and Masternode payments).

The govsync message initiates a sync of the governance system. Masternodes ignore this request if they are not fully synced.

There are two distinct stages of governance sync:

Initial request (object sync) - requests the governance objects only via a govsync message sent with a hash of all zeros.
Follow up request(s) (vote sync) - request governance object votes for a specific object via a govsync message containing the hash of the object. One message is required for each object. Dash Core periodically (~ every 6 seconds) sends messages to connected nodes until all the governance objects have been synchronized.

{% highlight text %} Dash Core limits how frequently the first type of sync (object sync) can be requested. Frequent requests will result in the node being banned. {% endhighlight %}

Masternodes respond to the govsync message with several items:

First, the Masternode sends one ssc message (Sync Status Count) for govobj objects and one for govobjvote objects. These messages indicate how many inventory items will be sent.
Second, the Masternode sends inv messages for the govobj and govobjvote objects.

Once the syncing node receives the counts and inventories, it may request any govobj and govobjvote objects from the masternode via a getdata message.

Governance Sync Data Flow

Sentinel

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Sentinel is a Python application that connects to a masternode's local dashd instance to run as an autonomous agent for persisting, processing, and automating Dash 12.1+ governance objects and tasks. Sentinel abstracts some governance details away from Dash Core for easier extensibility of the governance system in the future. This will allow the integration between Evolution and Dash Core to proceed more smoothly and enable new governance object additions with minimal impact to Dash Core.

Sentinel runs periodically and performs four main tasks as described below: governance sync, ping, governance object pruning, and superblock management. The governance object data is stored in a SQLite database.

Sentinel Sync

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Sentinel issues a gobject list RPC command and updates its database with the results returned from dashd. When objects are removed from the network, they are purged from the Sentinel database.

Sentinel Ping

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In Dash Core 12.2, use of the watchdog governance object type was replaced by integrating sentinel information into the masternode ping (mnp message) via Pull Request #1491. Sentinel calls the sentinelping RPC which updates the masternode info to prevent it from entering a MASTERNODE_WATCHDOG_EXPIRED state.

Sentinel Prune

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Sentinel 1.1.0 introduced proposal pruning which automatically votes to delete expired proposals following approximately half of a superblock cycle. This delay period ensures that proposals are not deleted prematurely. Prior to this, proposals remained in memory unless a sufficient number of masternodes manually voted to delete them.

Sentinel Superblock

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Sentinel manages superblock creation, voting, and submission to dashd for network propagation.

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Quorum Selection

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Dash quorums are used to facilitate the operation of masternode provided features in a decentralized, deterministic way.

Quorum Type	Members	Consensus	Description
InstantSend	10	Majority	A set of 10 masternodes are selected for each input of the InstantSend transaction. A majority (6+) of them must agree to lock the input. If all inputs in the transaction can be locked, it becomes a successful InstantSend.
MN Payments	10	Majority	A set of 10 masternodes are selected for each block. A majority (6+) of them must agree on the masternode payee for the next block.
MN Broadcast	10	Majority	If a majority (6+) of nodes agree, a new `mnb` message is not required.

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30 KiB Raw Blame History

Dash Features

InstantSend

PrivateSend

PrivateSend Wallet Preparation

PrivateSend Mixing

PrivateSend Fees

Masternode Payment

Masternode Sync

Initial Masternode Sync

Ongoing Masternode Sync

Masternode Sync Schedule

Governance

Synchronization

Sentinel

Sentinel Sync

Sentinel Ping

Sentinel Prune

Sentinel Superblock

Quorum Selection

30 KiB

Raw Blame History