How i convert Raw seed to Private Key in Substrate

Question

I have a toy example : My keypair is ed25519

const seed = [
   40, 246, 184,  64,  69, 145, 132, 131,
  231,  66, 112, 159, 162,  36,  79, 197,
   62,  54, 222, 103, 122, 190,   7, 143,
   94, 190, 180,  76,  87, 182, 115, 236
]

seed is Uint8Array(32) type

How I convert seed into private key in Substrate with polkadotjs api

Answer 1

You can get the Keypair and with it you can obtain the Public Key, the Address and sign transactions.

But the keyring does not expose the private key. It manages all signing operations on your behalf.

A code example to do that from your seed:

const keyring = new Keyring({ type: 'ed25519' })
const seed = [
    40, 246, 184,  64,  69, 145, 132, 131,
   231,  66, 112, 159, 162,  36,  79, 197,
    62,  54, 222, 103, 122, 190,   7, 143,
    94, 190, 180,  76,  87, 182, 115, 236
 ]
// add the account, encrypting it, override to ed25519
const keys = keyring.addFromSeed(Uint8Array.from(seed), { name: 'hex seed acc' },'ed25519');
console.log(keys.publicKey);
console.log(keys.address);
const signature = keys.sign("message");
console.log(signature);