AES KeyPairGenerator Not Recognised

Question

I have an issue with my java code. I'm trying to encrypt a file. However, when I run my java code I get "java.security.InvalidKeyException: Invalid AES key length: 162 bytes".

Here is the code:

byte[] rawFile;
File f = new File("./src/wonkybox.stl");
FileInputStream fileReader = new FileInputStream(f);
rawFile = new byte[(int)f.length()];
fileReader.read(rawFile);

/*****   Encrypt the file (CAN DO THIS ONCE!)  ***********/

//Generate the public/private keys
KeyPairGenerator keyGen = KeyPairGenerator.getInstance("AES");
SecureRandom random = SecureRandom.getInstance("SHA1PRNG","SUN");
keyGen.initialize(1024, random);
KeyPair key = keyGen.generateKeyPair();
PrivateKey privKey = key.getPrivate();
PublicKey pubKey = key.getPublic();

//Store the keys
byte[] pkey = pubKey.getEncoded();
FileOutputStream keyfos = new FileOutputStream("./CloudStore/keys/pubkey");
keyfos.write(pkey);
keyfos.close();

pkey = privKey.getEncoded();
keyfos = new FileOutputStream("./CloudStore/keys/privkey");
keyfos.write(pkey);
keyfos.close();


//Read public/private keys
KeyFactory keyFactory = KeyFactory.getInstance("AES");
FileInputStream keyfis = new FileInputStream("./CloudStore/keys/pubkey");
byte[] encKey = new byte[keyfis.available()];
keyfis.read(encKey);
keyfis.close();

X509EncodedKeySpec pubKeySpec = new X509EncodedKeySpec(encKey);
PublicKey pub1Key = keyFactory.generatePublic(pubKeySpec);

keyfis = new FileInputStream("./CloudStore/keys/privkey");
encKey = new byte[keyfis.available()];
keyfis.read(encKey);
keyfis.close();

PKCS8EncodedKeySpec privKeySpec = new PKCS8EncodedKeySpec(encKey);
PrivateKey priv1key = keyFactory.generatePrivate(privKeySpec);

//Encrypt file using public key
Cipher cipher = Cipher.getInstance("AES");
System.out.println("provider= " + cipher.getProvider());
cipher.init(Cipher.ENCRYPT_MODE, pub1Key);


byte[] encryptedFile;
encryptedFile = cipher.doFinal(rawFile);

//Write encrypted file to 'CloudStore' folder
FileOutputStream fileEncryptOutput = new FileOutputStream(new File("./CloudStore/encrypted.txt"));
fileEncryptOutput.write(encryptedFile);
fileEncryptOutput.close();

The error occurs at the line "KeyPairGenerator keyGen = KeyPairGenerator.getInstance("AES");".

Answer 1

AES is a symmetric algorithm, hence they use of KeyPairGenerator is not supported. To generate a key with AES you call KeyGenerator

KeyGenerator kgen = KeyGenerator.getInstance("AES");
       kgen.init(128);  //set keysize, can be 128, 192, and 256

By looking at the rest of your code, it looks like you are trying to achive asymmetric encryption (since you call getPublic() and getPrivate() etc), so I advice you to switch to using RSA or any other asymmetric algorithm that java supports. You will most likley only need to replace AES with RSA in your getInstance(); calls, and pherhaps some fine-tuning. Good luck

Answer 2

As far as I know, AES is symmetric encryption algorithm i.e. it needs only one key for encryption/decryption.

From the JavaDoc of java.security.KeyPairGenerator:

The KeyPairGenerator class is used to generate pairs of public and private keys.

Meaning that it should be used for asymmetric encryption algorithms. For symmetric encryption algorithms one should use javax.crypto.KeyGenerator.

However, I advise simply mimicking some tutorial on how to encrypt / decrypt byte array in Java using AES like this one.

It uses sun.misc.Base64Encoder / Base64Decoder classes to encode / decode byte array to / from String, however you may skip this step.

Hope this helps

Answer 3

How can you use a keypair generator for AES? AES is a symmetric key algorithm. Refer this link. That means if you encrypt data using a key "k", then you will have to decrypt it also using the same key "k".

But when you generate key pair, as the name suggests, two keys are generated and if you encrypt using one of the keys, you can decrypt only using the other key. This is the base for PKI.

If you want to use keypair generator use an algorithm like "rsa" or "dsa" in the getInstance() method like this :

KeyPairGenerator keygen=KeyPairGenerator.getInstance("rsa");

I think your code should now work fine after making the above change.