How to Encrypt/Decrypt text in a file in Java

Question

I have a problem with my code, when I encrypt data, for example, in this case, the simmetric key I encrypted with the receiver's public key, then saved to a text file, when I read that text file and try to decrypt it, using the receiver's private key, I get a different key, therefore I cannot use it to decrypt the encrypted message.

Sender's code:

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.security.KeyStore;
import java.security.MessageDigest;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import org.apache.commons.codec.binary.Base64;

class Sender{

public static void main(String[] args) {
        //infile.txt
        File inFile = new File(args[0]);
        //outfile.txt
        File outFile = new File(args[1]);
        //mykeystore.jks
        File keyStoreFile = new File(args[2]);
        //mykeystore info
        String alias = args[3];
        String password = args[4];
        String storepass = args[5];
        //receptor certificate
        String receptorCert = args[6];

        try {
            //Read plain text
            FileInputStream rawDataFromFile = new FileInputStream(inFile);
            byte[] plainText = new byte[(int) inFile.length()];
            rawDataFromFile.read(plainText);

            //Create simmetric key
            String key = "Bar12345Bar12345"; // 128 bit key
            String initVector = "RandomInitVector"; // 16 bytes IV
            IvParameterSpec iv = new IvParameterSpec(initVector.getBytes("UTF-8"));
            SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes("UTF-8"), "AES");
            Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
            cipher.init(Cipher.ENCRYPT_MODE, skeySpec, iv);

            //Encrypt plaintext
            byte[] ciphertext = cipher.doFinal(plainText);

            //Hash plaintext
            MessageDigest md = MessageDigest.getInstance("SHA");
            md.update(plainText);
            byte[] digest = md.digest();

            //Encrypt simmetric key with receiver's public key          
            Cipher rsaCipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
            PublicKey receptorPublicKey = getPublicKeyFromCert(receptorCert);
            rsaCipher.init(Cipher.ENCRYPT_MODE, receptorPublicKey);
            byte[] simmetricKey = rsaCipher.doFinal(skeySpec.getEncoded());

            //Encrypt hash with my private key
            KeyStore myKeyStore = KeyStore.getInstance("JKS");
            FileInputStream inStream = new FileInputStream(keyStoreFile);
            myKeyStore.load(inStream, storepass.toCharArray());
            PrivateKey privatekey = (PrivateKey) myKeyStore.getKey(alias, password.toCharArray());
            rsaCipher.init(Cipher.ENCRYPT_MODE, privatekey);            
            byte[] encodedHash = rsaCipher.doFinal(digest);

            //Write to outputfile
            FileOutputStream outToFile = new FileOutputStream(outFile);

            outToFile.write(simmetricKey);
            outToFile.write(encodedHash);
            outToFile.write(ciphertext);

            outToFile.close();
            rawDataFromFile.close();
        } catch (Exception e) {
            e.printStackTrace();
            e.getMessage();
        }
    }
    public static PublicKey getPublicKeyFromCert(String certLocation) {
        PublicKey pub = null;
        try {
            InputStream inStream = new FileInputStream(certLocation);
            CertificateFactory cf = CertificateFactory.getInstance("X.509");
            X509Certificate cert = (X509Certificate) cf.generateCertificate(inStream);
            inStream.close();
            pub = (PublicKey) cert.getPublicKey();

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

Receiver's code:

import java.io.File;
import java.io.FileInputStream;
import java.security.KeyStore;
import java.security.PrivateKey;
import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import org.apache.commons.codec.binary.Base64;

public class Receiver {

    public static void main(String[] args) {
        //Sender's out file
        File inFile = new File(args[0]);
        //receiver's keystore
        File keyStoreFile = new File(args[1]);
        //receiver's keystore info
        String password = args[2];
        String alias = args[3];
        String storepass = args[4];
        //sender's cetificate
        File cert = new File(args[5]);

        try {
            //get Sender's out file
            FileInputStream rawDataFromFile = new FileInputStream(inFile);
            byte[] simmetricKey = new byte[256];
            byte[] hash = new byte[256];
            byte[] message;

            rawDataFromFile.read(simmetricKey);
            rawDataFromFile.read(hash);

            int b = rawDataFromFile.available();
            message = new byte[b];

            rawDataFromFile.read(message);
            //decrypt the simmetric key with receiver's private key
            KeyStore myKeyStore = KeyStore.getInstance("JKS");
            FileInputStream inStream = new FileInputStream(keyStoreFile);
            myKeyStore.load(inStream, storepass.toCharArray());
            PrivateKey privatekey = (PrivateKey) myKeyStore.getKey(alias, password.toCharArray());
            //
            Cipher deCipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
            deCipher.init(Cipher.DECRYPT_MODE, privatekey);

            byte[] key = deCipher.doFinal(simmetricKey);

            System.out.println(Base64.encodeBase64String(key));

        } catch (Exception e) {
            System.out.println("Error del sistema " + e);
            e.printStackTrace();
        }

    }

}

UPDATE:

Now I can decrypt the simmetric key using the receiver's private key. But I dont know how to create a decoder using the same argument when I encrypted the message.

Sender's code to encrypt plain text.

    String key = "Bar12345Bar12345"; // 128 bit key
    String initVector = "RandomInitVector"; // 16 bytes IV
    IvParameterSpec iv = new IvParameterSpec(initVector.getBytes("UTF-8"));
    System.out.println(iv.getIV());
    SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes("UTF-8"), "AES");
    Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
    cipher.init(Cipher.ENCRYPT_MODE, skeySpec, iv);
    byte[] ciphertext = cipher.doFinal(plainText);

Receiver's decryption 1

    SecretKeySpec keySpec = new SecretKeySpec(decryptedKeySpec, "AES");
    Cipher decoder = Cipher.getInstance("AES");
    decoder.init(Cipher.DECRYPT_MODE, keyspec);
    byte[] original = descipher.doFinal(message);

ERROR: Given final block not properly padded

Receiver's decryption 2

    SecretKeySpec keySpec = new SecretKeySpec(decryptedKeySpec, "AES");
    Cipher decoder = Cipher.getInstance("AES/CBC/PKCS5PADDING");
    decoder.init(Cipher.DECRYPT_MODE, keyspec);
    byte[] original = descipher.doFinal(message);

ERROR: Parameters missing

FINAL UPDATE: Now my code works, thanks for all the help. This code can be downloaded from here (btw, it's in spanish, but i don't think it matters):

download

Answer 1

The issue is you are using AES to encrypt

SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes("UTF-8"), "AES"); Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");

whereas to decipher, you are using RSA,

Cipher deCipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");

Code snippet to use for encrypt/decrypt using AES

import java.util.Base64;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;

public class EncryptionDecryptionAES {
    static Cipher cipher;

    public static void main(String[] args) throws Exception {
        KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
        keyGenerator.init(128);
        SecretKey secretKey = keyGenerator.generateKey();
        cipher = Cipher.getInstance("AES");

        String plainText = "AES Symmetric Encryption Decryption";
        System.out.println("Plain Text Before Encryption: " + plainText);

        String encryptedText = encrypt(plainText, secretKey);
        System.out.println("Encrypted Text After Encryption: " + encryptedText);

        String decryptedText = decrypt(encryptedText, secretKey);
        System.out.println("Decrypted Text After Decryption: " + decryptedText);
    }

    public static String encrypt(String plainText, SecretKey secretKey)
            throws Exception {
        byte[] plainTextByte = plainText.getBytes();
        cipher.init(Cipher.ENCRYPT_MODE, secretKey);
        byte[] encryptedByte = cipher.doFinal(plainTextByte);
        Base64.Encoder encoder = Base64.getEncoder();
        String encryptedText = encoder.encodeToString(encryptedByte);
        return encryptedText;
    }

    public static String decrypt(String encryptedText, SecretKey secretKey)
            throws Exception {
        Base64.Decoder decoder = Base64.getDecoder();
        byte[] encryptedTextByte = decoder.decode(encryptedText);
        cipher.init(Cipher.DECRYPT_MODE, secretKey);
        byte[] decryptedByte = cipher.doFinal(encryptedTextByte);
        String decryptedText = new String(decryptedByte);
        return decryptedText;
    }
}

Please check http://javapapers.com/java/java-symmetric-aes-encryption-decryption-using-jce/