Generate RSA Key and Sign a String

Demonstrates how to generate a new RSA public/private key pair and use it to generate a signature for a string. The (binary) digital signature is returned as a hexidecimalized string.

Download Chilkat Java Library

import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    CkRsa rsa = new CkRsa();

    //  Any string argument automatically begins the 30-day trial.
    boolean success;
    success = rsa.UnlockComponent("30-day trial");
    if (success != true) {
        System.out.println("RSA component unlock failed");
        return;
    }

    //  Generate a 1024-bit RSA key pair.
    rsa.GenerateKey(1024);

    //  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");

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

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

    System.out.println(hexSig);
    System.out.println(rsa.lastErrorText());

    //  Now verify the signature:
    success = rsa.VerifyStringENC(strData,"md5",hexSig);
    if (success == true) {
        System.out.println("Signature verified!");
    }
    else {
        System.out.println(rsa.lastErrorText());
    }

    //  Try it with an invalid signature:
    success = rsa.VerifyStringENC(strData,"md5","not a valid sig");
    if (success == true) {
        System.out.println("Signature verified!");
    }
    else {
        System.out.println(rsa.lastErrorText());
    }

    //  Try it with invalid data:
    success = rsa.VerifyStringENC("Not the original data","md5",hexSig);
    if (success == true) {
        System.out.println("Signature verified!");
    }
    else {
        System.out.println(rsa.lastErrorText());
    }

    //  Try it with the wrong hash algorithm:
    success = rsa.VerifyStringENC(strData,"sha-1",hexSig);
    if (success == true) {
        System.out.println("Signature verified!");
    }
    else {
        System.out.println(rsa.lastErrorText());
    }

  }
}