Date: Thu, 6 Jul 1995 18:44:16 EDT From: "Randy Nichols, ACA Pres." <75542.1003@compuserve.com> GERMAN REDUCTION CIPHERS Part I TRAFFIC ANALYSIS A small sister to cryptanalysis is the applications of traffic analysis (TA). TA was the forerunner to differential cryptanalysis and a primary reason for the cracking of the German Codes in WWII. {Unfortunately, the same principles worked on the British and American Codes as well.} The German Army (maybe even the German Soul) was dedicated to unquestioned organization. Paperwork and radio messages must flow to the various military units in a prescribed manner. Traffic Analysis is the branch of signal intelligence analysis which deals with the study of external characteristic of signal communications. The information is used: 1) to effect interception, 2) to aid cryptanalysis, 3) to rate the level and value of intelligence in the absence of the specific message contents and 4) to improve the security in the communication nets. COMPONENTS Allowing for differences in language and procedure signs and signals, there are six standard elements for military radio communications systems. These are: 1) call-up, 2) order of traffic, 3) transmission of traffic, 4) receipting for traffic, 5) corrections and services, and 6) signing off. In order to insure proper handling of messages in the field and message center, some information was sent in the clear or using simple coding. This information about routing and accounting was usually in the preamble or message postamble. This included: 1) Serial numbers, message center number, 2) Group Count, 3) File Date and Time [like a PGP signature] 4) Routing System - origin, destination and relay, (distinction is made as to action or FYI locations) 5) Priority (important stuff was originally signal flashed - hence the term FLASH message for urgent message) 6) transmission and delivery procedure, 7) addresses and signatures, 8) special instructions. As a general rule, German high-echelon traffic contained most of these items and German low-echelon traffic cut them to a minimum. The German penchant for organization could be seen in the way they handled serial numbers. Any radio message flowing from division level to soldier in the field would have a reference serial number attached in clear or matrix cipher, by the writer, the HQ message center, the signal center or code room, the "in desk" , the transmitter, linkage, and/or operator. The routing system usually consisted of a code and syllabary that represented the location or unit. An example taken from WWII U. S. Army procedure: A45 BR6 B STX-O-P P-A45 BR6-T-N-A45 A-79K 011046Z A-45-W-F2P SLW BR6 GR 28 BT TEXT BT 011046Z K where: A45 BR6 - multiple callup; receiving calls STX-O-P - transmitting call with precedence designation, OP= operational priority P-A45 - message priority to A45 only; to others routine BR6-T-N-A45 - BR6 to relay to all except A45 A-79K - originator of message 011046 - Date and Time Zulu used pre and postamble A-45 - action destination W-F2P SLW BR6 - Information destinations GR 28 Group Count.. note how small for such external information envelope You can see where modern E-Mail and word processing systems have made some of this information easier to handle by the portable desk idea but TA would still apply. American "cryptees' were adept in determining the German Order of Battle (OB) from their cryptonets (ex. from intercepts re limited distribution from corp to a theater). TA not only gave the locations but the communication relationships between units or groups of units in the field. Some German commands were allowed latitude in their compositions of codes and ciphers. This proved to be an exploitable fault in their security. ANALYSIS OF ROUTING American success in reconstructing German communication networks was partly do to the appropriate (and sometimes lucky) analysis of the routing system. The radio station could be tied into the code group. Crib techniques included focusing on the relay point, recognizing a book message crib to several locations, correlating the address and signature cribs, tagging the operational chatter, separating the addresses, using solved messages to give outright routing assignments, syllabary solutions and changes in the system itself. The textual features of the message gave valuable information. Tabulations of messages, text type, and volumes helped discriminate the practice and dummy traffic. Recognition of the communications net as OB often gave away the crypto-entity. APPLICATIONS TO CRYPTANALYSIS TA yields information via Crib messages, Isologs and Chatter. Crib messages assume a partial knowledge of the underlying plaintext through recognition of the external characteristics. Command sitrep reports, up and down German channels, were especially easy for American crypees. The origin, serial number range, the cryptonet id, report type, the file date and time, message length and error messages in the clear, gave a clear picture of the German command process. German OB, troop dispositions and movements were deduced by TA. An Isolog exists when the underlying PT is encrypted in two different systems. They exist because of relay repetition requirements, book messages to multiple receivers (spamming would have been a definite no-no), or error by the code clerk. American crypees were particularly effective in obtaining intelligence from this method. CONCLUSION Traffic analysis boils down to finding the contact relationships among units, tracking their movements, building up the cryptonet authorities, capitalizing on lack of randomness in their structures, and exploiting book and relay cribs. I submit that American intelligence was quite successful in this endeavor against the Germans in WWII. REFERENCES AND FURTHER READING: 1) TM 32-250, Fundamentals of Traffic Analysis (Radio Telegraph) Department of the Army, 1948. 2) AFM - 100-80, Traffic Analysis, Department of the Air Force, 1946. 3) W. Barker, ed., History of Codes and Ciphers in the U.S. During the Period between World Wars, Part II, 1930 - 1939., Agean Park Press, 1990. 4) L.D. Callimahos and W. F. Friedman, Military Cryptanalytics, Parts I -II, Agean Park Press, 1994. (Appendix 2) 5) L.D. Callimahos, Traffic Analysis and the Zendian Problem, Agean Park Press, 1984. (also available through NSA Center for Cryptologic History) 6) D. Kahn, Kahn on Codes, McMillian, New York, 1983. 7) FM 34-60, Counterintelligence, Department of the Army, February 1990.