(.NET Core C#) RSA Sign utf-8 Bytes of String to get Base64 RSA Signature

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Demonstrates how RSA sign the utf-8 byte representation of a string to get the signature in base64 format.

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// Assuming the smartcard/USB token is installed with the correct drivers from the manufacturer,
// this code can work on multiple platforms including Windows, MacOS, Linux, and iOS.

// Chilkat automatically detects and determines the way in which the HSM is used,
// which can be by PKCS11, Apple Keychain, Microsoft CNG / Crypto API, or ScMinidriver.

Chilkat.Cert cert = new Chilkat.Cert();

// Set the token/smartcard PIN prior to loading.
cert.SmartCardPin = "123456";

// Specify the certificate by its common name.
bool success = cert.LoadFromSmartcard("cn=chilkat-rsa-2048");
if (success == false) {
    Debug.WriteLine(cert.LastErrorText);
    return;
}

Debug.WriteLine("Signing with cert: " + cert.SubjectCN);

// Create a string to be hashed and signed.
Chilkat.StringBuilder sb = new Chilkat.StringBuilder();
bool crlfLineEnding = true;
int i;
for (i = 0; i <= 10; i++) {
    sb.AppendLine("This is a test.",crlfLineEnding);
}

Chilkat.Rsa rsa = new Chilkat.Rsa();

// Use the certificate's private key for signing.
success = rsa.SetX509Cert(cert,true);
if (success == false) {
    Debug.WriteLine(rsa.LastErrorText);
    return;
}

// Sign the SHA-256 hash of the utf-8 byte representation of the contents of sb
// Return the signature in base64 format.
rsa.EncodingMode = "base64";
rsa.Charset = "utf-8";
string stringToSign = sb.GetAsString();
string sigBase64 = rsa.SignStringENC(stringToSign,"sha256");
if (rsa.LastMethodSuccess == false) {
    Debug.WriteLine(rsa.LastErrorText);
    return;
}

Debug.WriteLine("RSA signature as base64: " + sigBase64);