Verify digital signature??

Question

I've seen the tutorials from java and so on but I cant get the thing work.
I have a .cer certificate so i want it to read like:
FileInputStream keyfis = new FileInputStream("C:\\Work\\java\\editorDeTexto\\cert.der");
        byte[] encKey = new byte[keyfis.available()];
        keyfis.read(encKey);
        keyfis.close();
        X509EncodedKeySpec pubKeySpec = new X509EncodedKeySpec(encKey);
        KeyFactory keyFactory1 = KeyFactory.getInstance("RSA");
        PublicKey pubKey = keyFactory1.generatePublic(pubKeySpec); ........The program cant read the FileStream, anyway when it reads the stream i get this error:
derInputStream.getLenght(): lenghtTag = 111 too big
I dont know how to solve this problem at all... this is my main problem.

Answer 1

Finally did it... after a lot of days searching:
public static PublicKey get(String filename)
        throws Exception {
        File f = new File(filename);
        FileInputStream fis = new FileInputStream(f);
        DataInputStream dis = new DataInputStream(fis);
        byte[] keyBytes = new byte[(int)f.length()];
        dis.readFully(keyBytes);
        dis.close();
        X509EncodedKeySpec spec =
          new X509EncodedKeySpec(keyBytes);
        KeyFactory kf = KeyFactory.getInstance("RSA");
        return kf.generatePublic(spec);
public static boolean verifySig(byte[] data, PublicKey key, byte[] sig) throws Exception {
        Signature signer = Signature.getInstance("SHA1withRSA");
        signer.initVerify(key);
        signer.update(data);
        return (signer.verify(sig));
      }The main problem is the public key, java dont read PEM files so you have to convert it.
The solution for all your problems are here:
[http://codeartisan.blogspot.com/2009/05/public-key-cryptography-in-java.html|http://codeartisan.blogspot.com/2009/05/public-key-cryptography-in-java.html]
[http://www.keyzam.com/forum/index.php?topic=4.0|http://www.keyzam.com/forum/index.php?topic=4.0]
Remember to stay put, and not become crazy... this is really difficult (The prove is that noone helps me).
Anyway thanks to all.
Good signing/checking.
Edited by: alrik11es on Aug 24, 2009 2:00 PM