Encrypted AES key too large to Decrypt with RSA (Java)
- by Petey B
Hello,
I am trying to make a program that Encrypts data using AES, then encrypts the AES key with RSA, and then decrypt. However, once i encrypt the AES key it comes out to 128 bytes. RSA will only allow me to decrypt 117 bytes or less, so when i go to decrypt the AES key it throws an error.
Relavent code:
KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
kpg.initialize(1024);
KeyPair kpa = kpg.genKeyPair();
pubKey = kpa.getPublic();
privKey = kpa.getPrivate();
updateText("Private Key: " +privKey +"\n\nPublic Key: " +pubKey);
updateText("Encrypting " +infile);
//Genereate aes key
KeyGenerator kgen = KeyGenerator.getInstance("AES");
kgen.init(128); // 192/256
SecretKey aeskey = kgen.generateKey();
byte[] raw = aeskey.getEncoded();
SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
updateText("Encrypting data with AES");
//encrypt data with AES key
Cipher aesCipher = Cipher.getInstance("AES");
aesCipher.init(Cipher.ENCRYPT_MODE, skeySpec);
SealedObject aesEncryptedData = new SealedObject(infile, aesCipher);
updateText("Encrypting AES key with RSA");
//encrypt AES key with RSA
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, pubKey);
byte[] encryptedAesKey = cipher.doFinal(raw);
updateText("Decrypting AES key with RSA. Encrypted AES key length: " +encryptedAesKey.length);
//decrypt AES key with RSA
Cipher decipher = Cipher.getInstance("RSA");
decipher.init(Cipher.DECRYPT_MODE, privKey);
byte[] decryptedRaw = cipher.doFinal(encryptedAesKey); //error thrown here because encryptedAesKey is 128 bytes
SecretKeySpec decryptedSecKey = new SecretKeySpec(decryptedRaw, "AES");
updateText("Decrypting data with AES");
//decrypt data with AES key
Cipher decipherAES = Cipher.getInstance("AES");
decipherAES.init(Cipher.DECRYPT_MODE, decryptedSecKey);
String decryptedText = (String) aesEncryptedData.getObject(decipherAES);
updateText("Decrypted Text: " +decryptedText);
Any idea on how to get around this?
