Decrypted String always returning Null

Question

Data fetched from server using

var request = var request = URLRequest(url: URL(string: "http://www.example.com/test.php")!)   
        request.httpMethod = "POST"   
        let akey:String =  txt_key.stringValue;   
        let email:String = txt_email.stringValue   
        let VAL:String="test"      
        var data="blah"   
        let postString = data   
        request.httpBody = postString.data(using: .utf8)   
        let task = URLSession.shared.dataTask(with: request) { data, response, error in   
            guard let data = data, error == nil else {                                                 /   
                print("error=\(error)")   
                return   
            }   
            if let httpStatus = response as? HTTPURLResponse, httpStatus.statusCode != 200 {           /   
                print("statusCode should be 200, but is \(httpStatus.statusCode)")   
                print("response = \(response)")   
            }   
            let responseString = String(data: data, encoding:  .utf8)   
            print(responseString)   
        }   
        task.resume()   

Decryption using

   func aesDecrypt(key:String, iv:String, options:Int = kCCOptionPKCS7Padding) -> String? {
        if let keyData = key.data(using: String.Encoding.utf8),
            let data = NSData(base64Encoded: self, options: .ignoreUnknownCharacters),
            let cryptData    = NSMutableData(length: Int((data.length)) + kCCBlockSizeAES128) {

            let keyLength              = size_t(kCCKeySizeAES128)
            let operation: CCOperation = UInt32(kCCDecrypt)
            let algoritm:  CCAlgorithm = UInt32(kCCAlgorithmAES128)
            let options:   CCOptions   = UInt32(options)

            var numBytesEncrypted :size_t = 0

            let cryptStatus = CCCrypt(operation,
                                      algoritm,
                                      options,
                                      (keyData as NSData).bytes, keyLength,
                                      iv,
                                      data.bytes, data.length,
                                      cryptData.mutableBytes, cryptData.length,
                                      &numBytesEncrypted)

            if UInt32(cryptStatus) == UInt32(kCCSuccess) {
                cryptData.length = Int(numBytesEncrypted)
                let unencryptedMessage = String(data: cryptData as Data, encoding:String.Encoding.utf8)
                return unencryptedMessage
            }
            else {
                return nil
            }
        }
        return nil
}

Even when responseString is not null,The following code always returns optional("")

 let unencode = String(describing: responseString!).aesDecrypt(key: "123456789012asdsadasd", iv: "iv-salt-string--")

Why is this happening ? Please advice.

Answer 1

Per MartinR's comment:

I have verified that "JDoNBXk21oJ9x15Bkv12uw==" is exactly the result of encrypting an empty string with your key and iv. The error is in your PHP script, not in the Swift code.

Therefore you need to resolve the error on the server.