AES-128 padded encryption/decryption with Railo, Java and AS3
I’ve recently been working on text file decryption using Railo server. My files were encrypted in ActionScript 3 with the powerful AES-128 algorithm. For more info on AS3 encryption see Hurlant Crypto demo.
My challenge was to decypt this heavily encrypted content on a different platform, i.e. Railo with underlying Java Cipher capabilities.
The 6 things I knew about the encrypted content were:
1. Encryption Method – AES
2. Mode – CBC (Cipher-block chaining)
3. Padding – PKCS5
4. Initialisation Vector (IV) – given hex string
5. Passphrase – given hex string
6. Encrypted text file saved in base64 encoded string.For my records, this is how I went about decrypting on Railo:
<cfscript> // Create some java objects IvParameterSpec = createObject("java", "javax.crypto.spec.IvParameterSpec"); Cipher = createObject("java", "javax.crypto.Cipher"); SecretKeySpec = createObject("java", "javax.crypto.spec.SecretKeySpec"); BASE64Decoder = createObject("java", "sun.misc.BASE64Decoder"); Str = createObject("java", "java.lang.String"); MessageDigest = createObject("java", "java.security.MessageDigest"); encryptedFileContent = "base64encodedcontent"; password = binarydecode("somehexpassphrase", "hex"); iv = binarydecode("somehexivstring", "hex"); skeySpec = SecretKeySpec.init(password, "AES"); ivSpec = IvParameterSpec.init(iv); cipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); encryptedContent = BASE64Decoder.decodeBuffer(encryptedFileContent); cipher.init(Cipher.DECRYPT_MODE,skeySpec,ivSpec); decryptedBytes = cipher.doFinal(encryptedContent); decryptedString = Str.init(decryptedBytes); </cfscript>
Now that we know how the decryption works, encrypting data on Railo should be a piece of cake. For example:
<cfscript> password = "somepassphrase"; stringToEncrypt = "stringToEncrypt"; md = MessageDigest.getInstance("MD5"); md.update(password.getBytes("UTF-8"), 0, password.length()); rawKey = md.digest(); skeySpec = SecretKeySpec.init(rawKey, "AES"); ivSpec = IvParameterSpec.init(rawKey); cipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); cipher.init(Cipher.ENCRYPT_MODE, skeySpec, ivSpec); encryptedbytes = cipher.doFinal(stringToEncrypt.getBytes()); </cfscript>
The only thing you need to be aware of is the format of parameters passed into encryption/decryption logic, and convert them appropriately. These parameters can be either plain, base64 or hex strings.
Who would’ve thought that reverse engineering could be som much fun
Cheers
Marko
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