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The Ethereum wallet app Blockwallet for iOS generates seed phrases with 24 words (BIP39).

Using their keytools I am able to get a private key.

How do I convert the private key into a 12 word seed phrase that works with Metamask?

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  • I found another way to import a private key into Metamask but I'd still like to know how to generate a 12 word seed from a private key. – neuhaus Nov 29 '17 at 14:04
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You cannot convert a private key into a seed.

The operation of deriving a public or private key from a seed is intentionally irreversible. The idea is to prevent someone who knows one of your public or private keys from discovering others.

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  • I think you are mistaken. After all I can generate a 24 word seed from any private key. But if you have something to back it up, please show it. – neuhaus Jun 15 '18 at 8:06
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    Seeds are converted into private keys by the process detailed in BIP 32 (github.com/bitcoin/bips/blob/master/bip-0032.mediawiki). Several of the steps are in this process are designed to be irreversible. If you have a process that can turn a private key into a 24 word seed (that can then derive the same private key), then I've never heard of it, and would be very interested. – James_pic Jun 15 '18 at 10:25
  • Thanks. Looks like the seed phrase just provides a seed that is run through SHA512 to generate the key, so it can't be reversed. Still, the original question was how to convert a 24 word seed into a 12 word seed, this should be doable. – neuhaus Jul 15 '18 at 18:01
  • Converting a 24 word seed to a 12 word seed is also impossible, but for different reasons. According to BIP 39, a mnemonic seed is converted into a binary seed using PBKDF2-SHA-512. To turn a 24 word seed into a 12 word seed, you'd need to find a 12 word seed that produced the same binary seed as the 24 word seed, which would constitute a seconds preimage attack on PBDKF2-SHA-512, which is believed to be impossible. – James_pic Jul 16 '18 at 11:14

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