One embodiment of a method of authenticating data comprises: receiving, at a device, data in a plurality of indexed packets transmitted by a data server, the data of the indexed packets being at least a portion of a larger data stream; receiving, at the device, from a data authentication server connected to the device by a network, a server-computed authentication value based on a subset of the data transmitted by the data server, the data authentication server having access to the data that was transmitted from the data server to the device; and comparing a device-computed authentication value based on a subset of the received data, corresponding to the subset of the data transmitted by the data server, with the server-computed authentication value in order to determine whether the subset of the data received at the device is authentic.