Duplicate openssl dgst -md5 -sign myKey.pem something.txt | openssl enc -base64 -A

Demonstrates how to duplicate the creation of an RSA signature produced by this OpenSSL command:

openssl dgst -md5 -sign myKey.pem something.txt | openssl enc -base64 -A

 Chilkat Java Library Downloads for Windows, Linux, and MAC OS X

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[])
  {
    CkPrivateKey pkey = new CkPrivateKey();

    //  Load the private key from an RSA PEM file:
    pkey.LoadPemFile("myKey.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) {
        System.out.println(rsa.lastErrorText());
        return;
    }

    //  Import the private key into the RSA component:
    success = rsa.ImportPrivateKey(pkeyXml);
    if (success != true) {
        System.out.println(rsa.lastErrorText());
        return;
    }

    //  OpenSSL uses BigEndian byte ordering:
    rsa.put_LittleEndian(false);

    //  The resulting signature will be a Base64 string:
    rsa.put_EncodingMode("base64");

    //  For simplicity, we're not loading
    //  the data to be signed from a file.  We are instead simply
    //  using a literal string value.
    String strData;
    strData = "This is the text to be signed.";

    //  Hash the input using MD5, and then sign the hash:
    //  Other valid hash algorithm choices are "md2" and "sha-1".
    String base64Sig;
    base64Sig = rsa.signStringENC(strData,"md5");

    System.out.println(base64Sig);

    System.out.println("Success!");

  }
}