DAO technical overview

'WORK IN PROGRESS' This document is a detailed technical overview of the Bisq DAO and BSQ token. Although outdated, please see Phase Zero: A plan for bootstrapping the Bisq DAO,for a high-level overview and rationale,

BSQ token

BSQ is a colored coin based on Bitcoin. One BSQ is represented by 100 bitcoin satoshis.

The colored coin concept does not require OpReturn data but uses the transaction graph to determine if a tx output originates in either the genesis tx or an issuance transaction.

BSQ inherits all the transaction rules from Bitcoin and adds some additional rules. Even though BSQ transactions do not require OP_RETURN, it will be used for certain specialized transactions (voting, compensation requests, etc). Aside from the ancestry to the genesis or an issuance transaction, there is another important rule: the outputs are parsed in a way that the first outputs are interpreted as BSQ as long there is sufficient BSQ value available from the inputs. So the order of BSQ and BTC outputs is essential! For inputs the order is irrelevant. Any violation of those rules would make BSQ invalid. There are many more details which are not currently covered in this document.

We use the Bisq P2P network as a carrier for content-rich data like that of proposals or voting. The blockchain is used for timestamping that data. Both the P2P network data and the tx are linked together and are used for creating network consensus.

BSQ is a result of blockchain-related data and P2P network data.

Infrastructure

The Bisq DAO is based on Bitcoin blockchain data as well as on data from the Bisq P2P network. Each Bisq application verifies the rules of the DAO. The degree of trust to data delivered from other nodes can be determined by the user. Running a full DAO node requires running bitcoind with RPC enabled. The DAO state can be rebuilt from the genesis transaction. The only remaining trusted entity are then the seed nodes which deliver past P2P network data. As seed node operators are bonded, risk for abuse is very limited. There are (at the moment) 8 seed nodes and all need to be in consensus on P2P network data. The user can see the consensus in the application (Network Monitor tab).

Nodes

A user can decide to run the application as lite node or full node. By default it runs as lite node as that does not require any additional setup.

Full nodes

A fully-validating BSQ node has the requirement to run a Bitcoin Core (bitcoind) node to provide the blockchain data for verification. The communication is done via RPC. The details about the setup can be found in the documentation folder of the source code repository.

Full nodes receive a notification from Bitcoin Core at each new block, scan the block for BSQ transactions and broadcast those to the Bisq P2P network. Every transaction with any BSQ input or output (issuance) is considered a BSQ transaction. The full node also listens to network messages from lite nodes which request BSQ blocks from a certain block height. The full node sends back the list of all blocks since the requested height. The bandwidth requirements for this will depend on the number of BSQ transactions, but rough estimations suggest that there will be no considerable issues. Bisq seed nodes are used as full nodes since those are the first nodes to which a user gets connected and we can use the existing connection to transmit the additional data early in the startup process.

Lite nodes

Most users will likely operate in lite node mode. They have to trust the seed node operators that they are not all colluding and holding data back. If at least one operator is honest the lite node can detect a conflict and would re-validate each block from the last snapshot or even from the genesis block. The UI will notify the user about conflicting data from seed nodes.

At startup, a lite node requests the missing BSQ blocks from the seed node and then validates those blocks to achieve a local state of valid and unspent BSQ outputs. In case of chain splits it can be that one of the seed nodes is on another chain and conflicting blocks get propagated. This would trigger a re-validation of all blocks from the latest snapshot for the lite node. The last received block would be considered the current state but the user will see a message saying there are conflicts (and that it is recommended to wait for more than one confirmation before considering a BSQ transaction as valid). Only after all full nodes (seed nodes) have the same state again will the lite node exit the "warning" state. If the user waits for a sufficiently high number of confirmations (4-6) he will not risk that his validation was based on an orphaned chain and that he could become victim of a double spend.

Seed nodes

Seed nodes act as providers for P2P network data and filtered blocks from the Bitcoin blockchain for lite nodes. When a node starts, it requests all P2P network data from several seed nodes.

External DAO monitor

Monitoring of DAO-related data and infrastructure will be added to the Bisq monitoring. This should help us spot any potential consensus or network conflict early.

This is not deployed at the moment, but will be integrated soon.

BSQ block explorer

The BSQ block explorer shows all BSQ transactions with some metadata (transaction type, etc). It gives also some statistical data about the network. It is a very basic version at the moment, but we are working on a more sophisticated version. Any BSQ transaction can be looked up in a normal Bitcoin block explorer as well, but of course those explorers will not show any DAO-related context. If looking up a BSQ address on a normal Bitcoin block explorer, a user needs to remove the B prefix so the address is considered a valid BTC address.

BSQ integration on bisq

The Bisq DAO and BSQ are fully integrated into the Bisq UI. It comes with a BSQ wallet and UI for creating proposals, participating in voting, and taking part in other DAO functions.

Wallet

The Bisq application provides an integrated BSQ wallet with basic features for receiving and sending BSQ, as well as a transaction history screen. The wallet is based on BIP 44and uses registered coin type 142. This provides extra protection against the risk of accidentally using the BSQ wallet as a BTC wallet (e.g., when restoring from seed words). To avoid users from needing to backup 2 different sets of seed words, we use the same seed for both the BSQ and the BTC wallets, even though they are stored in different files. To further avoid mixing BSQ with normal Bitcoin, we use a "B" as address prefix for BSQ addresses in the user interface. Internally that prefix does not exist, as a BSQ address is a normal BTC address, and BSQ transactions are normal BTC transactions.

BSQ token transactions and balances are represented inside the application but there is also a web-based BSQ block explorer.

A BSQ transaction is valid only after a blockchain confirmation. However, for better usability, we allow users to spend their own change outputs. This involves no risk, as a user would render all follow-up transactions invalid if he tries to double-spend. Unconfirmed BSQ received from others is not spendable.

Application internal DAO monitor

Inside the application we maintain a hash chain of states and P2P network data. The overall DAO state gets hashed at each new block which contains the previous hash, thus forming a chain of hashes. If the last hash is correct, all the previous must be correct as well. Each node receives the last 10 hashes from seed nodes and compares it with its local hash. If there is any conflict, it shows a warning and requests to rebuild the DAO state. At each new block, each peer broadcasts its local hash to its neighbors. That way, the node also receives hashes from normal peers.

Similar to DAO states, we also maintain a hash chain for proposal data and blind vote data. These hashes are created only once per voting cycle at an appropriate block height (i.e., when it is expected that the whole network has received all data).

There are valid cases when consensus could be temporarily broken. In case of a chain split, nodes can have different DAO states, as the Bitcoin block hash is part of the data, and if 2 nodes are on a different chain they will have different block hashes.

In case some P2P network data was not distributed well in the network, there may be temporary conflicts of the relevant hash chains. An application restart should usually resolve such issues. If not, rebuilding the DAO state forces all P2P network data to be reloaded.

Snapshots

To avoid reevaluating all history at each startup, we use a snapshot mechanism.

Every 20 blocks a snapshot mechanism is triggered. The current state is cloned and kept in memory, and if a previous clone exists, it is persisted. At the next snapshot trigger event, the last clone is persisted and a new clone is cached. In this way, the snapshot is always at least 20 blocks old.

The lite node requests the blocks since the latest snapshot only, so that will usually be 20-40 blocks (maximum). The only exception to this is on first startup after a new install, when a lite node only has the snapshot shipped with the binary—in this case, requested blocks might consume a bit more bandwidth.

If we maintain a monthly release schedule, there can be about 4500 blocks in a month, but even with that we expect not more than 1-5 MB of bandwidth to receive the initial blockchain data.

Snapshots shipped in releases

Each application release is updated with a recent snapshot version of the DAO state. This data will be used for new users who have not created their own snapshot yet. This saves new users from needing to download all historical data and rebuilding DAO state from genesis.

The user still can rebuild from genesis if he does not want to trust that developers have shipped a correct snapshot. Any discrepancy would be easily detected.

Blockchain related data

One part of the DAO is based on Bitcoin blockchain data. We only use the blockchain for timestamping. Transactions do not carry content-rich data—this data is stored on the Bisq P2P network.

List of possible BSQ transaction types:

• Genesis tx
• Transfer BSQ tx
• Trade fee tx
• Proposal tx
• Compensation request tx
• Reimbursement request tx
• Blind vote tx
• Vote reveal tx
• Lockup tx
• Unlock tx
• Asset listing fee tx
• Proof of burn tx

In addition, a transaction can be unverified, invalid or irregular.

Unverified is the default state for all unconfirmed BSQ transactions. Validation is done once a tx is confirmed.

Invalid transactions are transactions which have violated validation rules. BSQ are destroyed in such transactions.

Irregular transactions are transactions which are invalid with their intended use but have not destroyed their BSQ. An example is a proposal tx which got confirmed too late (not in proposal phase) and therefore is invalid as a proposal tx, but the BSQ is still valid to be spent.

Genesis tx

We use BTC from our donation address to fund the input for the genesis tx. We will issue 3 657 480 BSQ which is equivalent to 3.65748 BTC. The amount of 3 657 480 BSQ is the sum of the 2 500 000 BSQ which we distributed as symbolic testnet BSQ to past contributors back in July 2017 and 1 157 480 BSQ contributors have earned since we started the DAO Phase Zero in October 2017.

The outputs are the BSQ addresses of all contributors who have contributed to Bisq before we start the DAO on mainnet. All outputs are by definition valid BSQ. The genesis tx is funded with the exact amount, including the miner fee, so there is no change output.

Transfer BSQ tx

Sending BSQ to another address is a simple transaction without OpReturn. It requires a BSQ input for the transferred BSQ as well as a BTC input to cover the miner fee. The outputs are the receiver’s BSQ address, an optional BSQ change output, and an optional BTC change output.

A transaction to send 10 BSQ could look like this:

• Input 1: 30.00 BSQ (BSQ sender)
• Input 2: 0.01 BTC (required BTC for mining fee)
• Output 1: 10.00 BSQ (BSQ receiver)
• Output 1: 20.00 BSQ (BSQ change output back to sender)
• Output 2: 0.0095 BTC (BTC change output)
• Mining fee: 0.0005

In this case, we only used 9.50 BSQ of the 10.00 BSQ from the input. Since the second output is spending more than the remaining 0.50 BSQ, it is an invalid BSQ output so we consider it a BTC output. The remaining 0.50 BSQ which was not used in the first output will be used for the mining fee, thus reducing the mining fee which is paid from the BTC input (input 2).

Trade fee tx

We invalidate a small amount of BSQ for the trade fee payment. Since the burned amount is used as miner fee and not as a regular tx output, we are not restricted by the dust limit of 546 satoshis, and can spend fees as little as 0.01 BSQ (equivalent to 1 BTC satoshi). The fee is the difference of the BSQ input and the BSQ output.

• A BSQ trade fee payment tx could look like this (for a fee with 0.5 BSQ):
• Input 1: 10.00 BSQ
• Input 2: 0.1 BTC
• Output 1: 9.50 BSQ
• Output 2: 0.09950050 BTC change output
• Mining fee: 0.0005 (0.00049950 BTC + 0.00000050 BTC or 0.50 BSQ)

In this case, we only used 9.50 BSQ of the 10.00 BSQ from the input. Since the second output is spending more than the remaining 0.50 BSQ, it is an invalid BSQ output so we consider it a BTC output. The remaining 0.50 BSQ which was not used in the first output will be used for the mining fee, thus reducing the mining fee which is paid from the BTC input (input 2).