(Chilkat for Android™ API)
Create PKCS1 RSA Signature with PEM Private Key

Demonstrates how to load a private key from a PEM file and create a PKCS1 RSA digital signature.

Download: Chilkat for Android™ Java Libraries

// Important: Don't forget to include the call to System.loadLibrary
// as shown at the bottom of this code sample.
package com.test;

import android.app.Activity;
import com.chilkatsoft.*;

import android.widget.TextView;
import android.os.Bundle;

public class SimpleActivity extends Activity {
  // Called when the activity is first created.
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    TextView tv = new TextView(this);
    String outStr = "";

    CkPrivateKey pkey = new CkPrivateKey();

    //  Load the private key from an RSA PEM file:
    pkey.LoadPemFile("pvkey2_rsa.pem");

    boolean success;

    String pkeyXml;
    //  Get the private key in XML format:
    pkeyXml = pkey.getXml();

    CkRsa rsa = new CkRsa();

    //  Any string argument automatically begins the 30-day trial.

    success = rsa.UnlockComponent("30-day trial");
    if (success != true) {
        outStr += "RSA component unlock failed" + "\n";
        tv.setText(outStr);
        setContentView(tv);
        return;
    }

    //  Import the private key into the RSA component:
    success = rsa.ImportPrivateKey(pkeyXml);
    if (success != true) {
        outStr += rsa.lastErrorText() + "\n";
        tv.setText(outStr);
        setContentView(tv);
        return;
    }

    //  This example will sign a string, and receive the signature
    //  in a hex-encoded string.  Therefore, set the encoding mode
    //  to "hex":
    rsa.put_EncodingMode("hex");

    //  If some other non-Chilkat software is going to verify
    //  the signature, it is important to match the byte-ordering.
    //  The LittleEndian property may be set to true
    //  for little-endian byte ordering,
    //  or false  for big-endian byte ordering.
    //  Microsoft apps typically use little-endian, while
    //  OpenSSL and other services (such as Amazon CloudFront)
    //  use big-endian.
    rsa.put_LittleEndian(false);

    String strData;
    strData = "This is the string to be signed.";

    //  Sign the string using the sha-1 hash algorithm.
    //  Other valid choices are "md2", "md5", "sha256",
    //  "sha384", and "sha512".
    String hexSig;
    hexSig = rsa.signStringENC(strData,"sha-1");

    outStr += hexSig + "\n";

    outStr += "Success!" + "\n";
    tv.setText(outStr);
    setContentView(tv);
  }

  static {
      // Important: Make sure the name passed to loadLibrary matches the shared library
      // found in your project's libs/armeabi directory.
      //  for "libchilkat.so", pass "chilkat" to loadLibrary
      //  for "libchilkatemail.so", pass "chilkatemail" to loadLibrary
      //  etc.
      // 
      System.loadLibrary("chilkat");

      // Note: If the incorrect library name is passed to System.loadLibrary,
      // then you will see the following error message at application startup:
      //"The application <your-application-name> has stopped unexpectedly. Please try again."
  }
}