The DUDEK series used random symmetric keys provided on paper tapes, which were XORed by the unit with the plaintext provided from the teleprinter or recorded on different paper tapes. The DUDEK sets were to be used in conjunction with teleprinters like the Siemens/Ceska Zbrojovka T-100 or the RFT T-51. The maximum transmission speed was at 50 or 75 Baud. The system was cleared up to the top secret level by the Poles provided that it served within the Tempested environment. The last DUDEK sets were retired by the Policja as of January 1, 2011.