Please guide me on the issue of private key

Question

Hi All
I am working on application that requires to do encryption and decryption using public and public key. I need some guidance on how to implement this functionality. The only requirement is to have public key and private key in two different files. For public key i can get it from .cer certificate file but i do not have much idea of what feature in java is provided to read private key from file. The file is definately not the keystore file. Please guide me as to in what format the private key should be so that my java program could read it and do decryption.
Another thing is that the private and public key file will be provided by the client. I do not have any control on creating them. I will be given a location where i could find public and private key and passphrase for private key.
Basically i do not have any clue on what class or technique to use to read those
Thanks and Regards
Pankaj Tiwari

Answer 1

This is how i create the private and the public key files (Not the certificate file) :
KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
kpg.initialize(2048); // 2048 is the keysize.
KeyPair kp = kpg.generateKeyPair();
PublicKey publicKey = kp.getPublic();
PrivateKey privateKey = kp.getPrivate();
// Serialize to a file
ObjectOutput outPK = new ObjectOutputStream(new FileOutputStream("C:/Temp/PrivateKey.ser"));
outPK.writeObject(privateKey);
outPK.close();
This is how i verify the signature of a file :
File fileKey = new File("C:/Temp/KeyPair/publicKey.ser");
ObjectInputStream inPK = new ObjectInputStream(new FileInputStream(fileKey));
PublicKey publicKey = (PublicKey) inPK.readObject();
inPK.close();
// C:/Temp/myfile.zip.sign is the file that was generated when i signed my file C:/Temp/myfile.zip
String algorithm = "SHA1withRSA";
String myFile = "C:/Temp/myfile.zip";
File fileSign = new File("C:/Temp/myfile.zip.sign");
ObjectInputStream inSign = new ObjectInputStream(new FileInputStream(fileSign));
byte[] signature = (byte[]) inSign.readObject();
inSign.close();
Signature verif = Signature.getInstance(algorithm);
verif.initVerify(pubKey);
FileInputStream in = new FileInputStream(myFile);
int chVerif = 0;
while ((chVerif = in.read()) != -1) {
verif.update((byte)chVerif);
if (verif.verify(signature))
System.out.println("OK");
else
System.out.println("Error");