A method includes, in a mobile communication terminal, receiving a signal, which carries media content that has been encrypted after being compressed in accordance with a compression protocol having a plurality of predefined configurations. Each configuration specifies a respective compression mode of the compression protocol. The received signal is decrypted, and one or more parameters that define a configuration of the compression protocol that was used for compressing the media content are determined from the decrypted signal. An absence of match is detected when the determined one or more parameters do not match any of the plurality of predetermined configurations of the compression protocol. An error in decrypting the received signal is identified based on detecting the absence of a match.