Stream implementation for encrypted files

The following works for both encryption and decryption. If the Cipher has been initialised with javax.crypto.Cipher.ENCRYPT_MODE then it encrypts and if with javax.crypto.Cipher.DECRYPT_MODE then it decrypts..

public static void encryptOrDecryptFile(File ifile, Cipher cipher, File ofile) throws Exception

{

InputStream istrm = new FileInputStream(ifile);

istrm = new javax.crypto.CipherInputStream(istrm, cipher);

OutputStream ostrm = new FileOutputStream(ofile);

byte[] buffer = new byte[65536];

for (int len = 0; (len = istrm.read(buffer)) >= 0;)

{

ostrm.write(buffer, 0, len);

}

ostrm.close();

istrm.close();

}

If all you need is to read from an encrypted XML file then just wrap the FileInputStream in a CipherInputStream and use that as input to the SAX parser. To save then just wrap your FileOutputStream in a CipherOuputStream.

Message was edited by:

sabre150

sabre150a at 2007-7-14 21:46:11 >

> Thanks, it's helpful. A bit more clarification. If

> I'm going to use asymmetric algorithm, then should I

> use different Cipher instances for encryption and

> decryption? Like one of them initialized with private

> key and another with public.

I probably would have two instances but it is not strictly necessary since one can init() a cipher as often as one likes.

sabre150a at 2007-7-14 21:46:11 >