This article discusses the DeserializeSignature vulnerability, which allowed attackers to create invalid ECDSA signatures that were accepted by the Bitcoin network. An ECDSA digital signature is a cryptographic method for verifying the authenticity of digital messages or documents. In the Bitcoin ecosystem, signatures are required to authorize transactions, i.e., to prove that the owner of the coins actually agrees to their transfer.
However, in 2023, a bug was discovered in the DeserializeSignature function, which made it possible to generate incorrect signatures that some Bitcoin clients considered valid.
How DeserializeSignature Works
The DeserializeSignature function is responsible for converting a signature from a byte sequence into an object suitable for verification. It expects the data to be in a specific format, compliant with the ECDSA standard adopted in Bitcoin. The function checks the signature against the computed hash: if everything is correct, it returns true, otherwise, false. The problem was that the function did not verify the correctness of all signature parameters before deserialization, in particular, it did not check that the values of “R” and “S” were not zero. This allowed signatures with zero values to be created, which were mistakenly accepted by some clients as valid. As a result, an attacker could forge a transaction signature that would pass verification using DeserializeSignature with incorrect input data.
Potential Threats and Attack Examples
This vulnerability posed a serious threat to Bitcoin’s security. Attackers could:
- Steal bitcoins by creating invalid signatures to transfer someone else’s funds to their own addresses.
- Perform double-spending by using signatures with zero parameters to create two transactions with the same coins.
- Forge data in the blockchain by adding fake transactions with incorrect signatures, potentially altering balances.
- Attack the transaction confirmation system by sending fake signatures to the network for verification.
The DeserializeSignature Process
DeserializeSignature is the conversion of a byte sequence into a data structure suitable for verifying a transaction signature. In Bitcoin, the signature is created using the ECDSA algorithm and consists of two numbers: r and s. Signatures confirm the authenticity and integrity of transactions. The vulnerability arises if an attacker can alter the deserialization process and forge the signature data.
Deserialization Steps:
- Reading the bytes representing the signature (usually in DER format).
- Checking compliance with the DER format: length and data structure.
- Extracting the r and s components.
- Verifying that r and s are within valid limits (e.g., between 1 and n-1, where n is the order of the curve).
Main Risk Points
- Format verification errors: If the DER format is not checked correctly, invalid signatures may be accepted as genuine.
- Library vulnerabilities: Using insecure deserialization libraries can lead to buffer overflow attacks or arbitrary code execution.
- Insufficient value checks: If r and s are not strictly checked, it allows the creation of fake signatures.
- Timing attacks: If processing time depends on the values of r and s, an attacker may gain information about the private key.
The article further analyzes the results of the vulnerability research, mechanisms of its occurrence, consequences, and protection methods.
Impact on Cryptocurrency Security
The DeserializeSignature vulnerability is dangerous for several reasons:
- Funds can be stolen from users’ wallets.
- Trust in cryptocurrencies is undermined, which may reduce their popularity.
- Attacks are difficult to detect and prevent, making them especially dangerous.
Protection Methods
- Strict data validation during deserialization.
- Regular updates of software and wallets.
- Security audits to identify and fix vulnerabilities.
Research Objectives
- Identify vulnerable points in the deserialization process.
- Assess the possible damage to the Bitcoin network.
- Study existing protection methods.
- Develop recommendations to improve security.
Methodology and Vulnerability Analysis
Errors can occur during Bitcoin data deserialization, which are exploited by attackers. After identifying the vulnerability, a detailed analysis is conducted: its impact on security is assessed, and possible attack scenarios are considered. Current protection methods and their effectiveness are also examined.
To eliminate the vulnerability, it is proposed to:
- Implement stricter checks at the deserialization stage.
- Conduct regular security testing.
- Increase developer awareness of potential vulnerabilities.
Comparison with Previous Research
Previous studies have examined vulnerabilities in the ECDSA algorithm itself, which could lead to private key leakage, as well as attacks on the Bitcoin P2P network, such as double-spending and Sybil attacks. Unlike those, DeserializeSignature is a data processing problem that can be solved by improving deserialization checks, rather than changing algorithms or protocols.
Practical Section: Generating and Analyzing Vulnerable Transactions
The article demonstrates how, using machine learning modules (such as BitcoinChatGPT), a vulnerable Raw transaction structure can be created. An example of such a transaction and its analysis via decoding services are provided, showing that the sender and recipient addresses match, and the signature is generated with the vulnerability.
The process of obtaining a private key from a vulnerable transaction using specialized software (such as ATTACKSAFE ULTRA) and Python scripts is described. The steps are detailed: extracting R, S, Z parameters, running the attack script, calculating the private key, and verifying it matches the address.
Conclusions
The article reviews the main methods for analyzing the DeserializeSignature vulnerability: static and dynamic analysis, fuzzing with machine learning. The vulnerability poses a serious threat to Bitcoin, but active research and the development of security tools significantly reduce the risks. Key recommendations: regularly update software, conduct audits, improve data validation algorithms, and increase the knowledge level of developers and users.
Eliminating this vulnerability is crucial for increasing trust and security in cryptocurrencies. Reliable implementation of the deserialization process and strict control of signature parameters are the foundation of transaction security in Bitcoin.