I have a question. I used the website (https://www.mobilefish.com/download/ethereum/bip39.html) to generate a 12-words mnemonic(English word list) without password and got below:

"organ rate senior panel first task siren room deer excite bachelor project"

And the 512-bits seed is like: "53329c51c9416d4d2fe46ecd8edab1c9a5289b3366c98bb6ee843e7bd4242ee46b6be686aef697d23278062d8c033cf2788df96cc4f24375682f36eb9a66996d"

However, I tried to generate 512-bits seed by myself but failed.

I used online PBKDF2 SHA-512 Hashes: https://stuff.birkenstab.de/pbkdf2/

And entered like below but got wrong result. Message: organrateseniorpanelfirsttasksirenroomdeerexcitebachelorproject Salt: mnemonic Iterations: 2048 Key length: 64

What I got is: 559c3427c333595e3ef78cc19d7f412452a763a09b66c8c7da2b49ecf12cd5d51ae7cb9bffe9d33ca358a421e984b626053192eea36ba909d307df0fa9ceda60

Please help to answer it.... Thanks!

  • 1
    I see your question was answered and you got it working, but for those who may see this question later on I would like to point out that the Message in the PBKDF2 function is the Mnemonic Words separated by spaces, not concatenated one after the other.
    – Septem151
    Jan 19, 2020 at 15:22

1 Answer 1


Just as a side note: What you get from 12 words is a seed of 512 bit length because it was stretched with PBKDF2. The entropy is only 128 bit with 12 words (each word represents 11 bits of information ~= 132 bit with 4 bit checksum).

If you look at a library like https://github.com/bitcoinjs/bip39/blob/master/src/index.js for example, you see that the spaces between the words aren't removed. If you paste the original words into the PBKDF2 tool you get the correct seed.

  • Thanks for your reply! However, I don't think you have answered my question. In BIP32: To create a binary seed from the mnemonic, we use the PBKDF2 function with a mnemonic sentence (in UTF-8 NFKD) used as the password and the string "mnemonic" + passphrase (again in UTF-8 NFKD) used as the salt. The iteration count is set to 2048 and HMAC-SHA512 is used as the pseudo-random function. The length of the derived key is 512 bits (= 64 bytes). It indicates that using mnemonic sentense as the password and string "mnemonic" + passphrase as the salt.
    – Mooooo
    Jan 17, 2020 at 2:42
  • In point 3, I still can't generate the right 512-bits seed out with "9c76470ecfc577bc325ddf3949d844d6".
    – Mooooo
    Jan 17, 2020 at 2:53
  • Sorry, you are right. What I described was BIP32 (which does use HMAC-SHA512). I forgot that BIP39 also does key stretching already. I edited my answer.
    – guggero
    Jan 17, 2020 at 8:57

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