Assume that a company wants to use DES in order to encrypt messages to remotely control its manufacturing machines. The company uses different messages types of 8 ASCII characters length each. The message payloads consist of simple operational orders like starting machines, stopping them, speeding up, etc.
The company considers to run DES in OFB mode (i.e., as a stream cipher). Assuming the eavesdropper has somehow figured out that the majority of all exchanged messages carry the payload INACTIVE. What (if any) information can an eavesdropper infer?
Any suggestions ???