[Flutter]: How to get public key PEM string from the x509 certificate PEM string

Question

I need the way to extract PEM string of Public Key from the x509 certificate PEM string. Now i'm using basic_utils package, that can generate x509Certificate object from the giving PEM string. This x509Certificate object have publicKeyData field that has bytes field, that represents the public key bytes as String. However i cannot use this bytes to generate valid PEM string of public key.

So question is - how can i extract public key as PEM string from the certificate?

Thanks

Answer 1

For RSA public keys:

import 'package:convert/convert.dart';
import 'package:basic_utils/basic_utils.dart';

final bytes = hex.decode(cert.publicKeyData.bytes!);
final key = CryptoUtils.rsaPublicKeyFromDERBytes(Uint8List.fromList(bytes));
final pem = CryptoUtils.encodeRSAPublicKeyToPemPkcs1(key);

The Pkcs1 version of the encoder will bracket the PEM with BEGIN RSA PUBLIC KEY whereas the non-pkcs1 version will use BEGIN PUBLIC KEY.