(Android™) Verify an RSA Signature Against the Signed String

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Demonstrates how to validate an RSA Signature against the string that was signed.

Chilkat Android™ Downloads Android™ Java Libraries Android C/C++ 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 {

  private static final String TAG = "Chilkat";

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

    // Create the same string we previously signed in this example: 
    // RSA Sign utf-8 Bytes of String to get Base64 RSA Signature

    CkStringBuilder sb = new CkStringBuilder();
    boolean crlfLineEnding = true;
    int i;
    for (i = 0; i <= 10; i++) {
        sb.AppendLine("This is a test.",crlfLineEnding);
        }

    String base64_rsa_sig = "gWgpEXQqvXN6wh0MuFXPiw2xCb8cnmdizBT1TD1Tpm2GlJ8gnD59DGSj35GGXk1tM+mCOvMa2uW/9gmz8p6A90JLbn918i/2wKGvcde4wXnzPO7JADSNn2UwYzf3rp4/q/JrHv1GZETRJhABSFqTxOgdmdbEJQE/zijOSctCtQAM2CTb6t2BO8uHKSSUAwPH2cbeWxqsaVRLT4ruk5nZOxhoLgLMSjupiSzbE8zSTkkFOEHD+Mbb2xwg85AI0E4DsUnp+hLwwtS0blesgSyvtBY8oJODJeFcJsR7JDOTPdzHQHgJRl/2A4ij5xT91TpXy7ok43jhT6O9j7Q3qrafIQ==";

    // Get the public key to be used for signature verification.
    CkPublicKey pubKey = new CkPublicKey();
    boolean success = pubKey.LoadFromFile("rsaKeys/chilkat-rsa-2048.pem");
    if (success == false) {
        Log.i(TAG, pubKey.lastErrorText());
        return;
        }

    CkRsa rsa = new CkRsa();
    rsa.ImportPublicKeyObj(pubKey);

    // Verify the string against the signature.
    // We signed the utf-8 byte representation of the string, so we must indicate
    // to also validate against the utf-8 byte representation.
    rsa.put_Charset("utf-8");
    rsa.put_EncodingMode("base64");
    String signedString = sb.getAsString();
    success = rsa.VerifyStringENC(signedString,"sha256",base64_rsa_sig);

    if (success == false) {
        Log.i(TAG, rsa.lastErrorText());
        Log.i(TAG, "Signature invalid.");
        }
    else {
        Log.i(TAG, "Signature valid.");
        }


  }

  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."
  }
}