Dart

Understanding a few ECDSA Public Key Formats

See more ECC Examples

Describes a few ECDSA public key formats. Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // Here we have the output of the following openssl command:  openssl ec -in key.pem -pubout -text

  // Private-Key: (256 bit)
  // priv:
  //     0e:63:25:8a:73:3c:71:b6:c0:e7:a3:0f:94:b9:74:
  //     e0:be:bd:46:18:be:40:7e:66:9e:21:99:85:0e:ed:
  //     87:2d
  // pub:
  //     04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:
  //     b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:
  //     39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:
  //     2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:
  //     12:b7:b8:6a:43
  // ASN1 OID: prime256v1
  // NIST CURVE: P-256
  // writing EC key
  // -----BEGIN PUBLIC KEY-----
  // MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
  // Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
  // -----END PUBLIC KEY-----

  // The public key is shown in two different formats.
  // The first is this:

  // pub:
  //     04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:
  //     b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:
  //     39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:
  //     2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:
  //     12:b7:b8:6a:43

  // It is the ANSI X9.63 format.
  // 65-bytes are the uncompressed public key (04 || X || Y) 

  // This is the same public key, but in PEM format

  // -----BEGIN PUBLIC KEY-----
  // MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
  // Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
  // -----END PUBLIC KEY-----

  // It contains ASN.1 that more explicitly identifies the key type.
  // 
  // SEQUENCE (2 elem)
  //   SEQUENCE (2 elem)
  //     OBJECT IDENTIFIER 1.2.840.10045.2.1 ecPublicKey (ANSI X9.62 public key type)
  //     OBJECT IDENTIFIER 1.2.840.10045.3.1.7 prime256v1 (ANSI X9.62 named elliptic curve)
  //   BIT STRING (520 bit) 000001000101110100011010010011111101100110111101010010011001111011100...

  // PEM format can be loaded into a Chilkat public key object like this:

  final sbPem = CkStringBuilder();
  sbPem.append('-----BEGIN PUBLIC KEY-----\r\n');
  sbPem.append('MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET\r\n');
  sbPem.append('Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==\r\n');
  sbPem.append('-----END PUBLIC KEY-----\r\n');

  final pubKey1 = CkPublicKey();
  try {
    pubKey1.loadFromString(sbPem.getAsString());
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // The X9.63 format can be loaded like this:
  final sbHex = CkStringBuilder();
  sbHex.append('04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:');
  sbHex.append('b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:');
  sbHex.append('39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:');
  sbHex.append('2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:');
  sbHex.append('12:b7:b8:6a:43');

  // Get rid of the ":" chars.
  final numReplaced = sbHex.replace(':', '');

  // We'll need to convert hex to base64..
  final bdKey = CkBinData();
  bdKey.appendEncoded(sbHex.getAsString(), 'hex');

  final pubKey2 = CkPublicKey();
  try {
    pubKey2.loadFromString(bdKey.getEncoded('base64'));
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Let's get the key in pubKey2 as PEM.
  // It should be idential to the PEM above.
  print(pubKey2.getPem(true));

  // Here's the output.  You can see it's the same as the PEM above..

  // -----BEGIN PUBLIC KEY-----
  // MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
  // Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
  // -----END PUBLIC KEY-----
}