🧠Entropy Bias in BIP-39 Seed Phrase Generation By [GUIAR OQBA] . Security Researcher

👋 Hello Dev Community ,
I hope this post finds you well.

Over the past few months, I’ve conducted extensive security research into the generation and validation of BIP-39 mnemonic recovery phrases used across multiple blockchain ecosystems — including Ethereum, Solana, Bytecoin, and others.

During this analysis, I discovered a potential non-uniform entropy distribution in the generated seed phrases — a subtle but concerning irregularity that may compromise wallet security in specific scenarios.

🔍 Key Observations
High Word Frequency Bias
Certain words appear disproportionately as the first, middle, or last words in mnemonic sequences.

Example: Some words occurred over 300 times as the initial word in generated valid 12- or 24-word phrases.

Abnormal Validation Rates
From a test batch of 150,000 programmatically generated phrases, we observed:

✅ 9,600+ valid wallets for 12-word English phrases

✅ 14,000+ valid wallets for 24-word English phrases

✅ 8,000+ valid wallets for 24-word Czech phrases

Statistical Anomalies
These rates suggest that valid mnemonic discovery is not entirely random, potentially due to:

Biased word distribution

Flawed entropy sources

Weak random number generation (RNG)

🛡️ Potential Impact
If BIP-39 implementations across platforms are found to have biases or entropy flaws, it could reduce the effective search space — making brute-force or partial-recovery attacks more feasible.

This weakness might affect wallet providers or applications using BIP-39 without adequate entropy enhancements or post-generation entropy checks.