Signing message with certificate: JCE, IAIK or similar in IBM SDK 5.0

Question

So, I'm in a very difficult problem.
Using Java:
I've an enterprise certificate (in .p12 format) altogether with its public key ("password" string). Also I've a text message which I've to sign in PKCS7 format. I've been reading a lot and I've realized that there's no STANDARD implementation to do what I want to do. There is the JCE/JCA API and the Certification API, but they are just API's, no implementation. Here are the facts:
-I've to run the application in the IBM JDK 5.0 (AS400 system).
-My application actually works in the SUN JDK 6.0 using the IAIK security provider, but not using JCE, its a very ugly code which I dont know really what it does, but it works. When I put it on the IBM JDK 5.0 it fails (java nullpointer blah blah).
-IAIK Documentation says that it works on JDK 5.0. Yeah, it works, but in SUN implementation, not in IBM's.
Today I don't know what the heck to do, really. What do you think it's the best solution?
-Trying to make the IAIK code work in IBM SDK 5.0 by test-and-error method.
-Trying to sign the message using JCE and the IBM JCE provider (this is what I'm actually trying to do). It would be very nice if somebody provides something to read about (I've read lot of IBM/SUN documentation and I couldnt find anything useful for now.
-Trying to put the SUN JDK 6.0 in the AS400. This would be the easy solution but my bosses said that this is impossible and very dangerous, and additionally this wouldn't work.
-Also I've another code which uses the BouncyCastle provider but this doesn't work. Would this be better to learn how to use? I prefer using standards, though.
In conclusion:
I've 4 security providers: IBM, SUN, IAIK and BouncyCastle (just IAIK works, and I need IBM), and
I've 4 SDK's: IBM 5.0, IBM 6.0, SUN 5.0 and SUN 6.0 (just SUN/IBM 6.0 works, and I need IBM 5.0).
I would like any documentation useful to read. I would provide any information which could be important to answer my question.

Answer 1

But I hope this could fix it :(
My last code:
public static String firmar(String contenido, String certificado, String password)
     throws Exception {
          System.out.println(new Date() + ":: Signing using IAIK provider.");
          boolean dettached = true;
         boolean attributes = true;
         boolean CRLF = true;
         IAIK iaik = new IAIK();
        Security.addProvider(iaik);
       byte aByteInfoToSign[] = contenido.getBytes("UTF8");
        if(aByteInfoToSign == null)
            throw new IOException("Empty message.");
        byte digest[] = SHA1(aByteInfoToSign);
        String digestHEX = toHexString(digest);
        KeyStore keystore = KeyStore.getInstance("PKCS12");
        FileInputStream fileinputstream = new FileInputStream(certificado);
        keystore.load(fileinputstream, password.toCharArray());
        String alias = null;
        Enumeration enumeration = keystore.aliases();
        if(enumeration.hasMoreElements())
            alias = enumeration.nextElement().toString();
        else
             throw new KeyStoreException("Firmador IAIK: Empty Keystore.");
        Certificate certificate = keystore.getCertificate(alias);
        PrivateKey privatekey = (PrivateKey)keystore.getKey(alias, password.toCharArray());
         * Declared absolutely to avoid incompatibilities betwenn IAIK and Sun classes.
        iaik.x509.X509Certificate ax509certificate[] = new iaik.x509.X509Certificate[1];
        ax509certificate[0] = new iaik.x509.X509Certificate(certificate.getEncoded());
        IssuerAndSerialNumber issuerandserialnumber = new IssuerAndSerialNumber(ax509certificate[0]);
        SignerInfo asignerinfo[] = new SignerInfo[1];
        asignerinfo[0] = new SignerInfo(issuerandserialnumber, AlgorithmID.sha1, AlgorithmID.rsaEncryption, privatekey);
          Attribute aattribute[] = new Attribute[4];
          aattribute[0] = new Attribute(ObjectID.contentType, new ASN1Object[] {
               ObjectID.pkcs7_data
          aattribute[1] = new Attribute(ObjectID.signingTime, new ASN1Object[] {
               (new ChoiceOfTime()).toASN1Object()
          ObjectID oid = new ObjectID("1.2.840.113549.3.2");
          SEQUENCE seqRC2 = new SEQUENCE();
          seqRC2.addComponent(oid,0);
          seqRC2.addComponent(new INTEGER(40));
          SEQUENCE seqEncrypAlgoritmos = new SEQUENCE();
          seqEncrypAlgoritmos.addComponent(seqRC2);
          Attribute atributo = new Attribute(ObjectID.symmetricCapabilities,
                               new ASN1Object[] {seqEncrypAlgoritmos});
          aattribute[2] = atributo;
          aattribute[3] = new Attribute(ObjectID.messageDigest, new ASN1Object[]{ new OCTET_STRING(digest) });
        if(attributes)
            asignerinfo[0].setAuthenticatedAttributes(aattribute);
        byte byte0;
        if(dettached)
            byte0 = 2;
        else
            byte0 = 1;
        SignedData signeddata = new SignedData(digestHEX.getBytes(), byte0);
        signeddata.setCertificates(ax509certificate);
        signeddata.addSignerInfo(asignerinfo[0]);
        ContentInfo contentinfo = new ContentInfo(signeddata);
        if(!contentinfo.hasContent())
             throw new Exception("Couldn't create the sign");
        ByteArrayOutputStream result = new ByteArrayOutputStream();
        ByteArrayOutputStream source = new ByteArrayOutputStream();
        contentinfo.writeTo(source); // <-- here is the error (line 136)
        Base64OutputStream base64outputstream = new Base64OutputStream(result);
        base64outputstream.write(source.toByteArray());
        base64outputstream.flush();
        base64outputstream.close();
        String resFinal;
        if(CRLF)
             resFinal = result.toString();
        else
             resFinal = result.toString().replaceAll("[\r\n]+","");
//         resFinal = sinCRLF(result.toString());
        if(resFinal.equals(""))
            throw new Exception("Couldn't create the sign");
         * Restore the Security variable.
        Security.removeProvider(iaik.getName());
        return resFinal;
     private static byte[] SHA1(byte abyte0[])
        try
            MessageDigest messagedigest = MessageDigest.getInstance("SHA-1");
            byte abyte1[] = messagedigest.digest(abyte0);
            messagedigest.reset();
            return abyte1;
        catch(NoSuchAlgorithmException nosuchalgorithmexception)
             throw new Error("Configuration error",  nosuchalgorithmexception);
     private static String toHexString(byte abyte0[])
        StringBuffer stringbuffer = new StringBuffer();
        int i = abyte0.length;
        for(int j = 0; j < i; j++)
            byte2hex(abyte0[j], stringbuffer);
        return stringbuffer.toString().toUpperCase();
     private static void byte2hex(byte byte0, StringBuffer stringbuffer)
        char ac[] = {
            '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
            'a', 'b', 'c', 'd', 'e', 'f'
        int i = (byte0 & 0xf0) >> 4;
        int j = byte0 & 0xf;
        stringbuffer.append(ac);
stringbuffer.append(ac[j]);
}Using the IBM SDK 5.0, the error:iaik.pkcs.PKCSException: iaik.asn1.CodingException: iaik.asn1.CodingException: Unable to encrypt digest: No installed provider supports this key: (null)
     at iaik.pkcs.pkcs7.SignedData.toASN1Object(Unknown Source)
     at iaik.pkcs.pkcs7.SignedDataStream.toASN1Object(Unknown Source)
     at iaik.pkcs.pkcs7.ContentInfo.toASN1Object(Unknown Source)
     at iaik.pkcs.pkcs7.ContentInfo.writeTo(Unknown Source)
     at aeat.FirmadorIAIK.firmar(FirmadorIAIK.java:136)
... more irrelevant data...