getPublicKey function

Uint8List getPublicKey(dynamic privateKey, { bool isCompressed = true, })

Derives the public key from a private key using the P-256 curve.

• privateKey: The private key as a Uint8List or a hexadecimal string.
• isCompressed: Specifies whether to return a compressed or uncompressed public key. Defaults to true.

Returns:

• The public key as a Uint8List in the specified format.

Implementation

Uint8List getPublicKey(dynamic privateKey, {bool isCompressed = true}) {
  Uint8List privKeyBytes;
  if (privateKey is String) {
    if (privateKey.length != 64) {
      throw ArgumentError('Private key must be a 32-byte hexadecimal string.');
    }
    privKeyBytes = Uint8List.fromList(List<int>.generate(privateKey.length ~/ 2,
        (i) => int.parse(privateKey.substring(i * 2, i * 2 + 2), radix: 16)));
  } else if (privateKey is Uint8List) {
    if (privateKey.length != 32) {
      throw ArgumentError('Private key must be exactly 32 bytes.');
    }
    privKeyBytes = privateKey;
  } else {
    throw ArgumentError(
        'Private key must be a Uint8List or a hexadecimal string.');
  }

  final domain = ECDomainParameters('secp256r1');

  final privateKeyValue = BigInt.parse(
      privKeyBytes.map((byte) => byte.toRadixString(16).padLeft(2, '0')).join(),
      radix: 16);
  final privateKeyParam = ECPrivateKey(privateKeyValue, domain);
  final publicKeyPoint = domain.G * privateKeyParam.d;

  if (publicKeyPoint == null) {
    throw StateError('Failed to compute public key.');
  }

  if (isCompressed) {
    return Uint8List.fromList(publicKeyPoint.getEncoded(true));
  } else {
    return Uint8List.fromList(publicKeyPoint.getEncoded(false));
  }
}