RSAKeyCreation.java

import java.io.BufferedOutputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.security.InvalidAlgorithmParameterException;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.RSAKeyGenParameterSpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Arrays;


public class RSAKeyCreation {

	/**
	 * @param args
	 * @throws NoSuchAlgorithmException 
	 * @throws InvalidAlgorithmParameterException 
	 * @throws InvalidKeySpecException 
	 * @throws IOException 
	 */
	public static void main(String[] args) throws NoSuchAlgorithmException, InvalidAlgorithmParameterException, InvalidKeySpecException, IOException {
		if (args.length != 1) {
			System.out.println("Usage: java RSAKeyCreation <name>");
		}
		
		String name = args[0];
		
		// Beispiel: java RSAKeyCreation KMueller
		// erzeugt die Ausgabedateien KMueller.pub und  KMueller.prv
		RSAKeyGenParameterSpec rsaKeyGenParameterSpec = new RSAKeyGenParameterSpec(1024, RSAKeyGenParameterSpec.F4);
		KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
		keyPairGenerator.initialize(rsaKeyGenParameterSpec);
		
		KeyPair keyPair = keyPairGenerator.generateKeyPair();
		KeyFactory keyFac = KeyFactory.getInstance("RSA");
		
		X509EncodedKeySpec pubKey = keyFac.getKeySpec(keyPair.getPublic(), X509EncodedKeySpec.class);
		PKCS8EncodedKeySpec prvKey = keyFac.getKeySpec(keyPair.getPrivate(), PKCS8EncodedKeySpec.class);
		
		byte[] pubEncoded = pubKey.getEncoded();
		byte[] prvEncoded = prvKey.getEncoded();
		
		DataOutputStream pubOut = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(String.format("%s.pub",name))));
		DataOutputStream prvOut = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(String.format("%s.prv",name))));
		
		// 1. LŠnge des Inhaber-Namens (integer)
		pubOut.writeInt(name.getBytes().length);
		prvOut.writeInt(name.getBytes().length);
		
		// 2. Inhaber-Name (Bytefolge)
		pubOut.writeBytes(name);
		prvOut.writeBytes(name);
		
		// 3. LŠnge des SchlŸssels (integer)
		pubOut.writeInt(pubEncoded.length);
		prvOut.writeInt(prvEncoded.length);
		
		// 4. SchlŸssel (Bytefolge)
		pubOut.write(pubEncoded); // [X.509-Format]
		prvOut.write(prvEncoded); // [PKCS8-Format]
		
		// close
		pubOut.close();
		prvOut.close();
	}
}