Get ECDSAPublicKey, ECDSAPrivate from pem encoded string in Dart - flutter

Question

1) How to get ECDSAPublicKey, ECDSAPrivateKey from DER encoded pem string
2) How to Marshal and Unmarshal ECDSAPublicKey,ECDSAPrivateKey using PKCS8 or PKCS1
3) I got ECPublicKey from ECPrivateKey , How to get ECDSAPublicKey directly from pem string instead of getting it from private key
String pemPkString = '''-----BEGIN PRIVATE KEY-----
MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQg6ZuZLImVj3CA2IE3
21G5mOK65KL71ost37cf2wrc7WChRANCAATMME1IAtwwoD53/IBUOY0H+ua6LKHj
yMhGPi/8dPz9h5FMyXHJQmXI3yEmW/tnyIRu6Z8PmAsVvKX8CnSC9fY6
-----END PRIVATE KEY-----''';
String pemPubString = '''-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEzDBNSALcMKA+d/yAVDmNB/rmuiyh
48jIRj4v/HT8/YeRTMlxyUJlyN8hJlv7Z8iEbumfD5gLFbyl/Ap0gvX2Og==
-----END PUBLIC KEY-----''';
String msgToSign = "Hai this is test";
var domainParams = new ECDomainParameters("secp256k1");
void main() {
privateKey = parsePrivateKey(pemPkString);
publicKey = publicKeyFromPrivateKey(privateKey);
var privParams = new PrivateKeyParameter(privateKey);
var signParams =
() => new ParametersWithRandom(privParams, new NullSecureRandom());
generateSignature(new ECDSASigner(), signParams, msgToSign);
var verifyParams = () => new PublicKeyParameter(publicKey);
verifySign(new ECDSASigner(), verifyParams, msgToSign, signature);
}
ECPrivateKey parsePrivateKey(String pemPkString) {
List<int> encodedPkData = PemCodec(PemLabel.privateKey).decode(pemPkString);
BigInt d = decodeBigInt(encodedPkData);
return new ECPrivateKey(d, domainParams);
}
//Get ECPublicKey from ECPrivateKey
ECPublicKey publicKeyFromPrivateKey(ECPrivateKey privateKey) {
ECPoint Q = privateKey.parameters.G * privateKey.d;
return new ECPublicKey(Q, privateKey.parameters);
}
void generateSignature(
Signer signer, CipherParameters params(), String message) {
signer.reset();
signer.init(true, params());
signature =
signer.generateSignature(sha256.convert(utf8.encode(message)).bytes);
print("Signature ");
print(encodeSignatureToPem(signature));
}
void verifySign(Signer signer, CipherParameters params(), String message,
Signature signature) {
signer.reset();
signer.init(false, params());
var ok = signer.verifySignature(
sha256.convert(utf8.encode(message)).bytes, signature);
print("Verified $ok");
}
String encodeSignatureToPem(ECSignature signature) {
var topLevel = new ASN1Sequence();
topLevel.add(ASN1Integer(signature.r));
topLevel.add(ASN1Integer(signature.s));
var dataBase64 = base64Encode(topLevel.encodedBytes);
return dataBase64;
}