Solving Double-Spending Problem: Innovative Applications of GHOSTDAG Protocol and UTXO Model
In the digital finance realm, blockchain technology is disrupting traditional financial systems. However, as blockchain networks expand, the issue of double spending becomes increasingly prominent.
This article explores the risks of double spending and introduces how the problem is addressed on the Qitmeer Network through the GHOSTDAG protocol and UTXO model.
What is double spending?
In blockchain, double spending means using or sending the same funds more than once, which can jeopardize transaction reliability and security.
Traditional banking systems have lower risk of double spending since banks manage account balances and ensure transaction uniqueness. However, in decentralized blockchains without central validation, double spending becomes a concern.
Here’s a more convincing example to illustrate double spending:
Let’s say Alice wants to buy a cup of coffee. She initiates a transaction on blockchain, sending a certain amount of MEER to the coffee shop as payment. At the same time, Alice initiates another transaction, sending the same amount of MEER to another one of her accounts, attempting to transfer the funds elsewhere.
These two transactions almost simultaneously reach different nodes. Due to network delays and propagation times, this leads to the occurrence of double spending.
Although the coffee shop accepts Alice’s payment and provides the coffee unknowingly, when other nodes in the network detect the conflict, they discover that the same MEER was used in two transactions simultaneously. This results in one transaction being deemed invalid while the other is confirmed as valid.
Such behavior violates the core principles of blockchain technology, undermining the fairness and security of transactions, posing a potential threat to the entire system. Therefore, preventing double spending is one of the crucial issues that blockchain technology must address.
The risk of double spending
In classic blockchain, transactions are processed sequentially in a single chain structure, similar to tasks being handled one at a time at a bank counter. However, allowing blockchain networks to process blocks in parallel to increase speed could increase the risk of double spending. This could result in two transactions on the same chain being approved simultaneously, similar to using the same physical dollar bill to pay for two different items.
In the world of cryptocurrencies, money is intangible, so double spending can become a serious issue, threatening the trust and integrity of the entire system and even potentially leading to instability and fragmentation of the blockchain system.
Qitmeer’s solution: GHOSTDAG protocol and UTXO model
To prevent double spending, the Qitmeer network uses innovative consensus mechanisms, including the GHOSTDAG protocol and UTXO model, ensuring the uniqueness and consistency of each transaction to maintain system security and reliability.
GHOSTDAG protocol
The GHOSTDAG (Greedy Heaviest Observed Subtree Directed Acyclic Graph) protocol is a consensus protocol used in the Qitmeer network. It aims to address double spending issues in parallel block processing and ensure the order and consistency of transactions.
Unlike traditional blockchains, GHOSTDAG retains all branching chains and allows each block to have multiple parent blocks, forming a Directed Acyclic Graph (DAG).
GHOSTDAG determines the main chain by selecting the heaviest observed subtree, where weight refers to the cumulative Proof of Work of the blocks, and observed subtree refers to the path from the genesis block to the current block. This mechanism ensures the order and consistency of transactions, effectively preventing double spending issues.
UTXO model
The UTXO (Unspent Transaction Output) model is the ledger model adopted by the underlying BlockDAG network of Qitmeer. Unlike Ethereum’s account balance model, the UTXO model treats each unspent balance as a transaction output rather than an account.
In the UTXO model, each transaction output is considered an unspent coin that can be referenced and spent by subsequent transactions. When a transaction references an unspent output, it consumes that output and creates one or more new unspent outputs. This model is similar to physical coins in the real world, where once used, they cannot be reused by the same person.
The Qitmeer network ensures that each asset on the chain can only be used in one transaction through the UTXO model, thereby enhancing security and certainty, effectively preventing double spending issues, especially suitable for micropayment scenarios.
Principle
The Qitmeer network utilizes the GHOSTDAG protocol and UTXO model to address the risks of parallel blocks and double spending. The combination of these technologies ensures that each transaction can only be used once, even if transactions are processed in parallel.
The GHOSTDAG protocol ensures a universal consensus order for transactions, similar to the rulebook followed by bank tellers to ensure no confusion about the sequence of customers. Transactions are categorized into “blue” (main chain) and “red” (conflicting) groups, similar to how supervisors swiftly resolve teller disputes.
In the GHOSTDAG system, blocks are divided into “kernels” and “anticone”, allowing the system to handle conflicting transactions methodically. The UTXO model provides additional security:
In the UTXO system, users do not have balances like traditional bank accounts; instead, they have “unspent transaction outputs” from previous transactions. When spending digital assets, you’re essentially referencing an unspent output and declaring, “I’m using this”. Once used, the output is marked as spent and cannot be used again.
By innovatively combining the GHOSTDAG protocol and UTXO model technologies, the Qitmeer network ensures that once assets on the chain are used in a transaction, they cannot be reused elsewhere.
Summary
The combination of the GHOSTDAG protocol and the UTXO model provides Qitmeer with a powerful solution to the double-spending problem and ensures the integrity and security of transactions.
Leveraging the concurrent transaction capabilities of BlockDAG, even with thousands of transactions per block, the system can swiftly process transactions within a minute without loss or delay. This setup also provides additional certainty, ensuring that each transaction can only be spent once, laying the foundation for a high-performance blockchain network.
This intricate technological fusion enhances user trust in the blockchain system, bridging the gap between traditional banking operations and the forefront of digital finance, paving the way for a trusted future in finance.
