How to get a public key from private key and/or account id in NEAR protocol?

Question

There are various scenarios when you may possess either account id (this is public information) or own the private (secret) key (e.g. extract it from NEAR Wallet local storage), and you want to know the corresponding public key.

What are the options to get the relevant public keys?

Answer 1

NEAR protocol uses EdDSA signature, and thus ed25519 keys are used. Having a private (secret) key, you can derive the corresponding public key (but you cannot derive the private key from the public key). Most of the libraries that implement EdDSA signing allows to derive a public key from a secret key, and here is how you can do that with near-api-js:

const nearApi = require('near-api-js')

// NEVER SHARE your private (secret) keys! (The key I used below is not used anywhere)
const keyPair = nearApi.KeyPair.fromString('ed25519:43qKAz3LfCTWpTAZPgA1DGsuwbiAjyosXpDrw24efAGP8Q3TcrnoUzTQHNRF5EbNTR38GRVdsHai9sRnzVu755gU')

console.log(keyPair.getPublicKey().toString())

Thus, having the secret key, you can always get the corresponding public key offline.

If you don't have a secret key, you won't be able to sign transactions, but you may still want to know the public keys that belong to some user, in which case you can query NEAR protocol network through RPC:

http post https://rpc.testnet.near.org jsonrpc=2.0 id=dontcare method=query \
  params:='{
    "request_type": "view_access_key_list",
    "finality": "final",
    "account_id": "near.test"
  }'

or with cURL:

curl -X POST https://rpc.testnet.near.org -H 'content-type: application/json' --data \
  '{
    "jsonrpc": "2.0",
    "id": "dontcare",
    "method": "query",
    "params": {
      "request_type": "view_access_key_list",
      "finality": "final",
      "account_id": "near.test"
    }
  }'

In response you will find all the public keys with their permissions for a given (near.test) account id.