Is it possible to get root key from CLI generated private key?

Question

Objective

To load a private key generated by cardano-cli into cardano-serialization lib

Details

Using cardano-cli cardano-cli address key-gen, we get this:

{
    "type": "PaymentSigningKeyShelley_ed25519",
    "description": "Payment Signing Key",
    "cborHex": "582099n3n930d9n31b5b102h3vd9csa290c14e0898sn1d278f1939f3e4bed890675a"
}

Are we able to derive the root key? for example in this format:

xprv17qx9vxm6060qjn5fgazfue9nwyf448w7upk60c3epln82vumg9r9kxzsud9uv5rfscxp382j2aku254zj3qfx9fx39t6hjwtmwq85uunsd8x0st3j66lzf5yn30hwq5n75zeuplepx8vxc502txx09ygjgx06n0p

or seed phrase? for example:

bawdy identify skin design ... squash elbow aloof plain nerve verse reply near

Answer 1

You can use that key to sign transactions in cardano-serialization lib, but I believe you can't go back to a seed phrase or root key / other key derivations from it.

To use it for signing transactions, you can unwrap and create the PrivateKey like so:

const cbor_hex_key = "582019544c6b8de8e697c6efa3a1ea728559b063f77f52314fcd2fbce3b692c3e99f";
const unhex = Buffer.from(cbor_hex_key, "hex");
const decode = cbor.decode(unhex);
const privKey = PrivateKey.from_normal_bytes(decode)
console.log(privKey.to_bech32()) // ed25519_sk1r92yc6udarnf03h05ws75u59txcx8aml2gc5lnf0hn3mdykrax0smqv6uc

(the cbor package for decoding is here: https://www.npmjs.com/package/cbor, the serialization lib pkg I use from here: https://www.npmjs.com/package/@emurgo/cardano-serialization-lib-nodejs)

If you do need to start from a root key starting with "xprv...", you can generate an extended key with the CLI using

cardano-cli address key-gen --extended-key

and then use that cborHex value in the serialization lib like so (it will be much longer than the one above):

const cbor_hex_ext_key = "5880a83391da55604678e05489ccb29cee99c238b224b29ef21f98dfd2b121155d5c9dfe7157214cd61c6522aaabb3a5707ae176b220516a51c2cc4f651a3c0dc21c0596b0c11795a9a42cf7ba0014fa402195900813942d66ba3c9b8c175e58fd5ac9e1dfa7008b77af7616ab23a9250374d7c4d39041874cfad9116c204e9b372a"
const ext_unhex = Buffer.from(cbor_hex_ext_key, "hex");
const ext_uncbor = cbor.decode(ext_unhex);
const ext_key = Bip32PrivateKey.from_128_xprv(ext_uncbor)
console.log(ext_key.to_bech32()) // xprv14qeerkj4vpr83cz538xt988wn8pr3v3yk200y8ucmlftzgg4t4wfmln32us5e4suv53242an54c84ctkkgs9z6j3ctxy7eg68sxuy8xfu806wqytw7hhv94tyw5j2qm56lzd8yzpsax04kg3dssyaxeh9gtrw423

But from there also you won't be able to go back to a seed phrase, but in case you're coming from a seed phrase (eg generated via "cardano-address recovery-phrase generate") you can decode it in the lib like so:

const entropy = mnemonicToEntropy("theme debate amateur pudding young deal wealth bag neck victory language abandon tribe unlock rabbit fix visual spawn broom advice anger foam strong document");
const root = Bip32PrivateKey.from_bip39_entropy(
    Buffer.from(entropy, 'hex'),
    Buffer.from(''),
  )
console.log(root.to_bech32()); //xprv1xqdaf53cvc8cdnmx6wf0gz3pxq0kk7rfu7sfkac99tadxs2j0prqe3n20emyw8vv7r8435lw2h4lgar2jwzdyfha7facnln0mhw22dlxgpgw38pt0vus0lyq9rs5rnws79x4dswwyklyklvyuyslh65c4ykl0hr4

Good source for all this: https://github.com/Emurgo/cardano-serialization-lib/blob/4f717ac97bd768168ab273dacd9e43cb6b4aa4ec/doc/getting-started/generating-keys.md)