Android™

Verify the RSA Signature of a SHA256 Hash

See more RSA Examples

Demonstrates how to verify an RSA signature of a SHA256 hash. Android™

// 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 {

  private static final String TAG = "Chilkat";

  // Called when the activity is first created.
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    boolean success = false;

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

    // Let's say you have a file containing the 32-bytes of a SHA256 hash,
    // and a file that is an RSA signature of those 32 bytes.
    // Here's how you verify using the RSA public key found in a PEM.

    CkPublicKey pubKey = new CkPublicKey();
    success = pubKey.LoadFromFile("rsaPubKey.pem");
    if (success == false) {
        Log.i(TAG, pubKey.lastErrorText());
        return;
        }

    CkRsa rsa = new CkRsa();

    // Get the public key.
    success = rsa.UsePublicKey(pubKey);
    if (success == false) {
        Log.i(TAG, rsa.lastErrorText());
        return;
        }

    // Get the 32-byte SHA256 hash.
    CkBinData bdHash = new CkBinData();
    success = bdHash.LoadFile("myHash.sha256");
    if (success == false) {
        Log.i(TAG, "Failed to load SHA256 hash.");
        return;
        }

    // Get the RSA signature to be validated.
    CkBinData bdSig = new CkBinData();
    success = bdSig.LoadFile("mySig.sig");
    if (success == false) {
        Log.i(TAG, "Failed to load RSA signature.");
        return;
        }

    // Verify the signature against the SHA256 hash.
    String enc = "base64";
    rsa.put_EncodingMode(enc);
    success = rsa.VerifyHashENC(bdHash.getEncoded(enc),"sha256",bdSig.getEncoded(enc));
    if (success == false) {
        Log.i(TAG, rsa.lastErrorText());
        return;
        }

    Log.i(TAG, "Signature validated.");

  }

  static {
      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."
  }
}