A robust property of transform encryption coding for channel and quantization noise is presented. In transform encryption coding, the
signal is prefiltered before transform coding. Therefore, a postfiltering process is necessary to reconstruct the signal from the transform coding. It is shown thatthe prefiltered signal is unrecognized and, thus, that signal encryption is achieved. Owing to the requisite postfiltering process, the channel and quantization noise spread all over the reconstructed signal from transform encryption coding, and become less visible. In addition, transform encryption coding not only increases the compression ratio, quality, noise insensitivity, and security level of the coded signal but also removes the blocking effect. It can be considered, therefore, as a combined source-channel coding scheme and is suitable for the applications related to noisy channel communications.