(.NET Core C#) RSA SHA256 Signature using Private Key from Java Keystore

Signs plaintext using RSA SHA256 using a key from a Java keystore.

Duplicatest this code:

KeyStore keystore; // key repository for keys containing signature certificate
String alias; // alias for the certificate in the key repository
String password; // password for the certificate's private key
String plaintext; // text being signed


Signature signature = Signature.getInstance("SHA256withRSA");
signature.initSign((PrivateKey) keystore.getKey(alias, password.toCharArray()));
signature.update(plaintext.getBytes("UTF-8"));
byte[] rsa_text= signature.sign();

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// This requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

Chilkat.JavaKeyStore jks = new Chilkat.JavaKeyStore();

string jksPassword = "secret";

// Load the Java keystore from a file.  The JKS file password is used
// to verify the keyed digest that is found at the very end of the keystore.
// It verifies that the keystore has not been modified.
bool success = jks.LoadFile(jksPassword,"qa_data/jks/sample_secret.jks");
if (success != true) {
    Debug.WriteLine(jks.LastErrorText);
    return;
}

// Get the private key from the JKS.
// The private key password may be different than the file password.
string privKeyPassword = "secret";
bool caseSensitive = false;
Chilkat.PrivateKey privKey = jks.FindPrivateKey(privKeyPassword,"some.alias",caseSensitive);
if (jks.LastMethodSuccess != true) {
    Debug.WriteLine(jks.LastErrorText);
    return;
}

// Establish the RSA object and tell it to use the private key..
Chilkat.Rsa rsa = new Chilkat.Rsa();

success = rsa.ImportPrivateKeyObj(privKey);

if (success != true) {
    Debug.WriteLine(rsa.LastErrorText);
    return;
}

// Indicate we'll be signing the utf-8 byte representation of the string..
rsa.Charset = "utf-8";

// Sign some plaintext using RSA-SHA256
byte[] binarySignature = null;
string plaintext = "this is the text to be signed";
binarySignature = rsa.SignString(plaintext,"SHA256");
if (rsa.LastMethodSuccess != true) {
    Debug.WriteLine(rsa.LastErrorText);
    return;
}

// Alternatively, if the signature is desired in some encoded string form,
// such as base64, base64-url, hex, etc.
rsa.EncodingMode = "base64-url";
string signatureStr = rsa.SignStringENC(plaintext,"SHA256");
Debug.WriteLine("base64-url RSA signature: " + signatureStr);