Potential Weakness In BIP-39 Mnemonic Entropy Distribution Across Multiple Languages

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Introduction

As the use of blockchain technology continues to grow, the importance of secure wallet management has become increasingly crucial. One of the most widely used methods for generating and validating wallet recovery phrases is the BIP-39 standard. However, during extensive research into the generation and validation of BIP-39 mnemonic recovery phrases across multiple blockchain ecosystems, I have observed what appears to be non-uniform entropy distribution in the structure of generated seed phrases.

Background

BIP-39 is a widely adopted standard for generating and validating wallet recovery phrases. It uses a combination of words from a predefined list to create a unique and secure phrase that can be used to recover a wallet. The standard is designed to be language-agnostic, allowing users to generate phrases in their native language. However, my research has revealed potential weaknesses in the entropy distribution of generated seed phrases across multiple languages.

Key Observations

High Frequency of Certain Words

During my analysis, I observed that certain words appear disproportionately as first, middle, or last words in valid mnemonic phrases. For example, some words appeared more than 300 times as initial words in generated valid phrases. This suggests that the word selection process may be biased, potentially allowing attackers to narrow down the search space and recover access to real wallets.

Abnormal Validation Rates

From a test batch of 150,000 phrases, I observed the following validation rates:

  • Over 9,600 valid wallets for 12-word English phrases.
  • Over 14,000 valid wallets for 24-word English phrases.
  • Over 8,000 valid wallets for 24-word Czech phrases.

These results indicate that the validation process may be vulnerable to bias, potentially allowing attackers to recover access to real wallets.

Non-Random Recovery Patterns

Statistical anomalies indicate that valid phrase recovery might not be entirely random. The probability of success at this scale would be extremely low unless a pattern or reduction in entropy exists. This suggests that the generation of seed phrases may be vulnerable to bias, potentially allowing attackers to recover access to real wallets.

Impact

If such entropy weaknesses exist in the generation of seed phrases—whether due to implementation flaws, poor random number generation (RNG), or biased word selection—they may allow attackers to narrow down the search space and potentially recover access to real wallets. This issue could impact any wallet providers or platforms relying solely on BIP-39 without sufficient entropy enhancement or post-generation randomness checks.

Ethical Research Notes

No private user data was accessed or misused. The wallets referenced in this study were identified exclusively using statistical and analytical methods. All actions were performed in a controlled, non-exploitative environment for security research purposes. I am fully committed to responsible disclosure and open to further collaboration to ensure ecosystem safety.

Additional Information

  • GitHub Issue Opened: Issue on Trezor GitHub.
  • Pull Request on Bitcoin BIP-39 GitHub: Pull Request on Bitcoin BIP-39 GitHub.
  • Communication with Cardano: I reached out to the Cardano team regarding this issue, and they requested that I publish it on their forum at forum.cardano.org.
  • Publication on dev.io: I also published this research on dev.io to share the findings with the broader developer community and stimulate discussion on improving mnemonic phrase security.

Suggested Areas for Further Investigation

  • Audit BIP-39 implementations for bias in mnemonic generation.
  • Test the RNG quality of commonly used wallet providers.
  • Introduce additional entropy-hardening layers or recommend entropy audits in BIP-39 usage.
  • Review the impact of language-specific word distributions on security.

Supporting Materials Available Upon Request

  • Scripts used for phrase generation and analysis.
  • Frequency distribution charts for seed word positions.
  • Datasets of non-funded/generated wallet addresses for research validation.
  • Short video demonstration of phrase validation logic (excluding any sensitive data).

Final Note

The purpose of sharing this issue is to strengthen the security of BIP-39-based systems and ensure that user funds remain safe in the long term. I welcome any input from the community and relevant maintainers.

Additional Communication

I have contacted Cardano about this issue, and they requested that I post it on their forum at forum.cardano.org. The issue has also been published on dev.io.

Q: What is BIP-39 and why is it important?

A: BIP-39 is a widely adopted standard for generating and validating wallet recovery phrases. It uses a combination of words from a predefined list to create a unique and secure phrase that can be used to recover a wallet. BIP-39 is important because it provides a secure way for users to recover their wallets in case they lose access to their private keys.

Q: What is the potential weakness in BIP-39 mnemonic entropy distribution?

A: The potential weakness is that certain words appear disproportionately as first, middle, or last words in valid mnemonic phrases. This suggests that the word selection process may be biased, potentially allowing attackers to narrow down the search space and recover access to real wallets.

Q: How did you discover this potential weakness?

A: I conducted extensive research into the generation and validation of BIP-39 mnemonic recovery phrases across multiple blockchain ecosystems. I analyzed a large dataset of programmatically generated phrases, using legal and ethical methods, without targeting or accessing any unauthorized data.

Q: What are the implications of this potential weakness?

A: If the potential weakness is confirmed, it could allow attackers to recover access to real wallets. This could have significant consequences for users who rely on BIP-39 for wallet recovery.

Q: How can wallet providers and platforms mitigate this potential weakness?

A: Wallet providers and platforms can mitigate this potential weakness by implementing additional entropy-hardening layers or recommending entropy audits in BIP-39 usage. They can also test the RNG quality of commonly used wallet providers and audit BIP-39 implementations for bias in mnemonic generation.

Q: What is the current status of this research?

A: I have published this research on dev.io and have opened a GitHub issue on Trezor's GitHub repository. I have also communicated with the Cardano team regarding this issue and have requested that they publish it on their forum.

Q: What is the next step in this research?

A: The next step is to conduct further investigation into the potential weakness. This will involve auditing BIP-39 implementations for bias in mnemonic generation, testing the RNG quality of commonly used wallet providers, and introducing additional entropy-hardening layers or recommending entropy audits in BIP-39 usage.

Q: How can the community get involved in this research?

A: The community can get involved by reviewing the research and providing feedback. They can also help to audit BIP-39 implementations for bias in mnemonic generation and test the RNG quality of commonly used wallet providers.

Q: What is the ultimate goal of this research?

A: The ultimate goal of this research is to strengthen the security of BIP-39-based systems and ensure that user funds remain safe in the long term.

Q: Who is behind this research?

A: I am Okba GUIAR OQBA, a security researcher who is committed to responsible disclosure and open to further collaboration to ensure ecosystem safety.

Q: How can I stay up-to-date with this research?

A: You can stay up-to-date with this research by following the GitHub issue on Trezor's GitHub repository and the publication on dev.io. You can also follow me on social media to stay informed about the latest developments in this research.