Question

I have an encrypted email id for unsubscribing from abcde.test.com.

for ex : https://abcde.test.com/Forms/unSubscribe.jsp?n=2&rid=00028e7353d9c4eca480a579e10ef09b&eid=588876054d458e62779be9345f399252cac7346ad8c464b8ed0bdfbff3512dd96a5b4190c5d71c30c90c34ff39e544aa

This is encrypted in aes-256.where eid=”encrypted message” and rid when combined with keysize,and keystr (like “6a6b663472346c38736873346569727538346234333534376635333962353666”) forms the encoded key.

Now I want to decrypt this message.
can any one help me decrypting it?

Answer 1

Try the following using Java SE and Apache Commons. Please note that you haven’t indicated the mode or padding for your cipher (just “AES”), so you might need to make some adjustments.

// decode the key string into bytes (using Apache Commons)
byte[] keyBytes = Hex.decodeHex(keystr.toCharArray());

// create a representation of the key
SecretKeySpec spec = new SecretKeySpec(keyBytes, "AES");

// turn the key spec into a usable key
SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("AES");
SecretKey key = keyFactory.generateSecret(spec);

// use a cipher to decrypt the eid
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.DECRYPT_MODE, key);
byte[] plainText = cipher.doFinal(hex.decodeHex(eid.toCharArray())); // decode from Hex again

I don’t know what type eid represents, so turning that into something concrete is up to you, but here’s an example:

String eid = new String(plainText, "ASCII");