(Java) Generate RSA Key and Sign a String

See more RSA Examples

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.

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

    CkRsa rsa = new CkRsa();

    // Generate a 2048-bit RSA key.
    boolean success = rsa.GenerateKey(2048);

    // To return the signature in hex.
    rsa.put_EncodingMode("hex");

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

    // Sign the SHA256 hash of the string.
    String hexSig = rsa.signStringENC(strData,"sha256");

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

    // Now verify the signature:
    success = rsa.VerifyStringENC(strData,"sha256",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,"sha256","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","sha256",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());
        }
  }
}