I have a private key for my wallet and also a keystore for it. I want to use it in MEWConnect. Is there a way to get a mnemonic phrase from a private key?


No, a mnemonic is generated using an hd wallet - a hierarchical deterministic wallet. Private keys are "children" of this mnemonic and there can be millions of them, but there's no way to go back to the parent having only a child private key.

You can generate a new mnemonic if you install MetaMask or most of the other Ethereum wallets out there (Status, Coinbase Wallet etc).

  • There’s absolutely no way to get mnemonic phrase from private key? – Incrediblez7 Nov 17 '18 at 22:12
  • Unfortunately no, that's not how cryptography in Ethereum or Bitcoin works! It'd be a massive security breach if you could do that. I'd recommend reading more on hierarchical deterministic wallets. – Paul Razvan Berg Nov 17 '18 at 22:14
  • Is there a way to convert back and forth from a 12 to a 24 words mnemonic phrase? – rraallvv Apr 9 '19 at 9:25
  • If you go from 24 words to 12 words you lose information, there's no way to recover it. – Dan Williams Feb 17 at 14:45

I concur with Paul Berg that there is no way to represent a single private key as a mnemonic, with the qualification that there is no STANDARD way which will automatically work with existing wallets or other utilities. If you wanted to create a mnemonic for backup with a custom algorithm you can use the BIP39 word list, which has 2048 words, and manually map bits of your private key to the corresponding word.

2048 equals 2^11 so you need to split up the 256 bits of your private key into 11-bit segments with padding/checksum added to make it a multiple of 11. A good way is to take the sha256 checksum of the private key and append the last 8 bits of it to the private key, so you get 264 bits, which map to 24 words.

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