Hi,

I have faced some problem related to generation of digital signature
on Microsoft .NET platform and it's verification on Java platform.

I create a digital signature in my C# (Microsoft ASP.NET) application.
The public/private keys are generated by another C# application and it
saves the key parameters to the XML files.
The public key XML files looks like following:
================================================================================
<DSAKeyValue>
<P>vMYiMuNfgygyNr9aMQQO5QWcoGobLmrcjcvee7RGVzUgAMD7XQMbkXNKw3DpYNrGpQxAgf9/g1fHRFvfIQmueGVcXCdhGuEgR85KeMwsbfOms75M2YDiZd+Txn2uq80RUvae2EgV9mEfJd4sILJqpbxdYNaam5IlK4erPIsDyhU=</P>
<Q>pm88Q93QPyKctcsbk2AEY9DQL2s=</Q>
<G>NY2afKKr7vWBON/JYuITdkAaRqfOq8j2CP4k/E5KFFEJsoXX0OTuA97SkGkFH4rI7duFBts8AgPMFT+4sol8hyBxlXZAk/mYNsOXbi+tGx+UjhVXr1q1Py1Oeh2nm9LFUvatf25mvnCXXaS7D5m6oDhisceFmj037+Tb0x4Rn2I=</G>
<Y>H08XX/n2aVwdHLygLUmOWyKu5tx20NX6fs2ZrgP2I6E1VKmYHQm3hhPRlQK6+48Vz+AmXDiqbO3Ptcbl01k847Zz+Fe8r9R9gGzjqFUcRSor5g7jZxIHaYVZ9NXsis6xt77AbhJ9mbKRFvqaddYvRuu6wOoBTL8wXTQFVV/1hMk=</Y>
<J>AAAAASJcevs9ahEe2/FWRzkVX3tKOumVUJY+0G+j1RK7X+klzqGUpO7Ih+KV4uw7DAakbP63489PReT8umGXzbcHhoXMuPFK/ziJCdnEvKbhgUQUCBmddpb0nGhNlGB3UoEPRfaYdoTztAMRNbZHPA==</J>
<Seed>EtzxtCwjIVklWmY8dtR0jtonX0Y=</Seed>
<PgenCounter>RA==</PgenCounter>
</DSAKeyValue>
================================================================================

In my Java application I create the PublicKey object using the
parameters P, G, Q, Y of the public key, that I get from the public
key XML, generated by my C# application.

//------------------------------------------------------------------------------
private PublicKey getPublicKey() throws Exception
{
    PublicKey publicKey = null;

    try
    {
        String sKeyFile = GetKeyFilePath(false);
        File keyFile = new File(sKeyFile);   
   
        DocumentBuilderFactory factory =
                               
DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document pubKeyXml = builder.parse(keyFile);
           
        BigInteger P = GetKeyParam(pubKeyXml, "P");
        BigInteger G = GetKeyParam(pubKeyXml, "G");
        BigInteger Q = GetKeyParam(pubKeyXml, "Q");
        BigInteger Y = GetKeyParam(pubKeyXml, "Y");
           
        DSAPublicKeySpec dsaPubKeySpec = new DSAPublicKeySpec(Y, P, Q,
                                                                   
G);
        KeyFactory keyFactory = KeyFactory.getInstance("DSA");
        publicKey = keyFactory.generatePublic(dsaPubKeySpec);
    }
    catch(Exception ex)
    {
        String msg = ex.getMessage();
        throw new Exception("getPublicKey(): " + msg);
    }
    return publicKey;
}
//------------------------------------------------------------------------------

private BigInteger GetKeyParam(Document keyXml, String paramName)
                                                        throws
Exception
{
    BigInteger biParam = null;
    try
    {
        String sParam = GetNodeValue(keyXml, paramName);
       
//        byte [] param = sParam.getBytes("UTF-8");
//        biParam = new BigInteger(param);

        biParam = new BigInteger(sParam);
    }
    catch (Exception ex)
    {
        String msg = ex.getMessage();
        throw new Exception("GetKeyParam(): " + msg);
    }
    return biParam;
   
}
//------------------------------------------------------------------------------

I try to verify the digital signature in my Java program.

But I get the "BigInteger not invertible." exception when I call the
verify() method of the Signature object.

I have tried to create & verify the signature in the same Java program
using the keys parameters, generated by C#  application,
but I get same exception.

If I generate the key pair in my Java application and use them to
create & verify the digital signature, all works fine.

I have also succeed to generate and verify the digital signature in my
C# applications, using the private/public keys parameters saved in XML
file.

I use the "DSA with SHA1" algorithm.

I suppose that the different byte-ordering in .NET and in Java causes
the problem.
.NET uses the little-endian format and Java uses the big-endian
format.

I have tried to save the XML with public key parameters to file using
the Encoding.BigEndianUnicode.
The "BigInteger not invertible." exception disappeared, but the the
verify() method of the Signature class returns false.

What encoding should I use in my GetKeyParam() method to convert the
string with key parameter to correct byte array and then to
BigInteger?

//            byte [] param = sParam.getBytes("UTF-8");
//            biParam = new BigInteger(param);

Regards,
Arkady