Disclosed are various examples for securing the transmission of files to and from a client device. In some examples, an initialization token is identified for a file that includes a number of portions. An algorithm is iteratively applied to the initialization token to determine that no repeated output occurs over a number of iterations corresponding to the number of file portions. Initialization data is transmitted from a client device to a management service that manages access to the file. The initialization token is included in the initialization data if no repeated output occurs when the algorithm is iteratively applied over the number of iterations.