RSA Encryption Decryption Class Demo

RSAEncDecDemo.java

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.RSAPrivateKeySpec;

import javax.crypto.Cipher;
import javax.xml.bind.DatatypeConverter;

import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;

public class RSAEncDecDemo {

	private static final String PUBLIC_KEY_FILE = "lk.public.key";
	private static final String PRIVATE_KEY_FILE = "lk.private.key";

	@SuppressWarnings("restriction")
	public static void main(String[] args) throws IOException {

		try {
			KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
			keyPairGenerator.initialize(2048);
			KeyPair keyPair = keyPairGenerator.generateKeyPair();
			PublicKey publicKey = keyPair.getPublic();
			PrivateKey privateKey = keyPair.getPrivate();

			writeStringkey(PUBLIC_KEY_FILE,new BASE64Encoder().encode(publicKey.getEncoded()));
			writeStringkey(PRIVATE_KEY_FILE,new BASE64Encoder().encode(privateKey.getEncoded()));

			String demoString = "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"; 
			RSAEncDecDemo rsa = new RSAEncDecDemo();
			String decrypted = rsa.decryptData(demoString);
			String msisdn = decrypted.substring(0,decrypted.indexOf("|"));

		} catch (Exception e) {
			e.printStackTrace();

		}
	}

	private String decryptData(String strData) throws IOException {
		byte[] data = DatatypeConverter.parseHexBinary(strData);
		byte[] descryptedData = null;

		try {
			PrivateKey privateKey = readPrivateKeyFromFile(PRIVATE_KEY_FILE);
			Cipher cipher = Cipher.getInstance("RSA");
			cipher.init(Cipher.DECRYPT_MODE, privateKey);
			descryptedData = cipher.doFinal(data);

		} catch (Exception e) {
			e.printStackTrace();
		}

		return new String(descryptedData);
	}


	@SuppressWarnings("restriction")
	public PrivateKey readPrivateKeyFromFile(String fileName)throws IOException, NoSuchAlgorithmException,InvalidKeySpecException {

		String publicK = readStringKey(fileName);
		byte[] keyBytes = new BASE64Decoder().decodeBuffer(publicK);
		PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(keyBytes);
		KeyFactory fact = KeyFactory.getInstance("RSA");
		return fact.generatePrivate(keySpec);
	}

	public PrivateKey readPrivateKeyFromFileold(String fileName)throws IOException {
		FileInputStream fis = null;
		ObjectInputStream ois = null;
		try {
			fis = new FileInputStream(new File(fileName));
			ois = new ObjectInputStream(fis);

			BigInteger modulus = (BigInteger) ois.readObject();
			BigInteger exponent = (BigInteger) ois.readObject();

			RSAPrivateKeySpec rsaPrivateKeySpec = new RSAPrivateKeySpec(modulus, exponent);
			KeyFactory fact = KeyFactory.getInstance("RSA");
			PrivateKey privateKey = fact.generatePrivate(rsaPrivateKeySpec);

			return privateKey;

		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			if (ois != null) {
				ois.close();
				if (fis != null) {
					fis.close();
				}
			}
		}
		return null;
	}

	public static void writeStringkey(String fileName, String data) {
		try {
			FileWriter out = new FileWriter(new File(fileName));
			out.write(data);
			out.close();
		} catch (IOException e) {
		}
	}

	public static String readStringKey(String fileName) {

		BufferedReader reader = null;
		StringBuffer fileData = null;
		try {

			fileData = new StringBuffer(2048);
			reader = new BufferedReader(new FileReader(fileName));
			char[] buf = new char[1024];
			int numRead = 0;
			while ((numRead = reader.read(buf)) != -1) {
				String readData = String.valueOf(buf, 0, numRead);
				fileData.append(readData);
				buf = new char[1024];
			}

			reader.close();

		} catch (Exception e) {
		} finally {
			if (reader != null) {
				reader = null;
			}
		}
		return fileData.toString();

	}
}