Question

i have a AESkey which encrypted by a public key, and later decrypted by a private key

    Cipher cipher = Cipher.getInstance("RSA");
    PrivateKey privateKey = keyPair.getPrivate();
    // decrypt the ciphertext using the private key 
    cipher.init(Cipher.DECRYPT_MODE, privateKey); 
    byte[] decryptedText = cipher.doFinal(theBytes); 

theBytes is a byte[] containing a encrypted AESkey, the question is how to convert the decryptedText back to the AESkey?

Answer 1

I believe you’re receiving an RSA-encrypted AES key along with some AES-encrypted data, and you still need to perform the second of 2 encryptions. Right?

So, anyway, you can load a key from the byte array.

SecretKeySpec secretKeySpec = new SecretKeySpec(decryptedText, "AES");

Subsequently you’d do something like this, to decrypt the AES-encrypted data, ‘encrypted’:

Cipher cipherAes = Cipher.getInstance("AES/CBC/PKCS7Padding");
cipherAes.init(Cipher.DECRYPT_MODE, secretKeySpec);
byte[] decryptedBytes = cipherAes.doFinal(encrypted);
String decryptedString = new String(decryptedBytes);

The /CBC/PKCS7Padding specification may vary, depending on how it was specified during encryption.

Hope this helps.