convert base64 to hex

base64ToHex.js

const crypto = require("crypto");

const keyAsTxt =
  "MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEgyYqQmUAmDn9J7dR5xl-HlyAA0R2XV5sgQRnSGXbLt_xCrEdD1IVvvkyTmRD16y9p3C2O4PTZ0OF_ZYD2JgTVA==";
const keyAsBytes = Buffer.from(keyAsTxt, "base64");
const keySpec = new Uint8Array(keyAsBytes);
const algo = { name: "ECDSA", namedCurve: "P-256" };

(async () => {
  
  const publicKey = await crypto.subtle.importKey("spki", keySpec, algo, true, [
    "verify",
  ]);
  
  // convert public key to hex string
  const publicKeyHex = Buffer.from(
    await crypto.subtle.exportKey("raw", publicKey),
  ).toString("hex");
  console.log(publicKeyHex);
  
  // remove the first byte (0x04) from the hex string
  const publicKeyHexWithoutPrefix = publicKeyHex.slice(2);
  
  // get x and y coordinates from the hex string
  const x = publicKeyHexWithoutPrefix.slice(0, 64);
  const y = publicKeyHexWithoutPrefix.slice(64);
  console.log("x: ", x);
  console.log("y: ", y);
})();

Thanks for the code