Limitations of Ethereum Signed Hashes: Understanding Tx Malleability

Ethereum’s blockchain technology has been widely adopted and used for a variety of decentralized applications, allowing users to create, send, and receive digital assets without the need for intermediaries. However, one aspect of Ethereum that can be frustrating for developers is its reliance on a specific cryptographic mechanism – the “signed hash” used to validate transactions (tx).

The tx field in an Ethereum tx contains not only the sender’s public key, but also their signature, which serves as proof of work to validate transactions. The tx field includes two important components: the signer’s signature and the signature. When a developer wants to sign a transaction, they create a new public-private key pair (signer’s private key and tx private key). However, there is an issue that can lead to a different transaction hash when changes are made to the signature or formatting.

In this article, we’ll dive deeper into why Ethereum’s script-based validation system is vulnerable to malleability. We’ll explore how changes to the tx field can result in different hashes, and we’ll look at some sources of tx malleability to gain more insight.

Understanding Script Malleability

Scripting is a crucial component of Ethereum transactions, allowing developers to create complex logic within each transaction. Scripts are used to determine whether an account balance meets the requirements for certain actions (e.g. sending or receiving tokens). However, scripts can be created in a variety of ways to bypass security restrictions.

When it comes to validation, script malleability becomes a significant concern. Any changes to the tx field that affect the signature or formatting can result in different hashes. This is because the tx field contains both public and private keys, as well as the signer’s signature. When the signer’s signature is changed, the hash of the tx field is affected.

Sources of Tx malleability

Sipa has listed some sources of tx malleability in their GitHub repository:

• Changes to the resignee signature: Any change to the resignee’s private key or the script that uses it will result in a different transaction hash.

• Changes to script formatting

  : Modifying the script code within the tx field can lead to altered hashes, as the script logic is embedded in the tx data structure.

The consequences of Tx malleability

Tx malleability poses significant risks to Ethereum developers and users. It allows attackers to create fake or forged transactions, potentially leading to:

• Phishing attacks: Attackers can create fake wallets and send tokens to unsuspecting users.

• Rogue transactions: Hackers can intercept and manipulate transactions without consent.

Conclusion

In conclusion, Ethereum’s script-based validation system is vulnerable to malleability. Changes to the tx field or its formatting can result in different hashes, leaving developers and users vulnerable to various types of attacks. To mitigate these risks, developers should:

• Keep your resign private keys secure

  : Regularly update and store resign private keys securely.

• Use secure script code: Ensure that scripts used in tx fields are crafted with caution and follow the specified format.

By understanding the limitations of Ethereum’s signed hash system and taking steps to address tx malleability, developers can help protect against malicious activity and ensure a more secure decentralized ecosystem.

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