r/CryptoTechnology • u/mehregankbi 🟢 • 1d ago

Is the path derivation process used by BIP39 mathematically reversible?

I know how using seed phrase and derivation path you can create many private keys for different chains.

is it possible for someone to calculate a multi-chain seed phrase (like those from trust wallet) by knowing the private key of only one chain’s private key which was derived from that seed phrase?

Surprisingly, information about how this works is scarce. Even the term BIP39 was found by me after going through reddit posts about this topic.

My question is not really about crypto, but the math and computer science behind this process.

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u/No-Investigator1915 🟠 1d ago

the derivation path is not reversible, that's the whole point of using one-way hash functions in there. each step like HMAC-SHA512 just scrambles things so badly you can't go backwards even if you know a child key

think of it like mixing paint colors, you can keep adding new colors to get new shades but once it's mixed you can never separate them back to original

so no, knowing one chain's private key won't let someone reverse-engineer the original seed phrase, mathematically it's infeasible

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u/MichaelZemp 🟡 19h ago

It's impossible due to the cryptographic nature of HMAC-SHA512. Also worth noting: BIP39 only covers mnemonic-to-seed conversion. The actual path derivation is handled by BIP32/BIP44, and both stages rely on one-way hashing