The 5-UCO (5-Unit Controlled)Ralph Erskine, "The 1944 Naval BRUSA Agreement and its Aftermath", ''Cryptologia'' 30(1), January 2006 pp14–15 was an on-line one-time tape Vernam cipher encryption system developed by the UK during

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

for use on

teleprinter A teleprinter (teletypewriter, teletype or TTY) is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point (telecommunications), point-to-point and point- ...

circuits. During the 1950s, it was used by the UK and the US for liaison on

cryptanalysis Cryptanalysis (from the Greek ''kryptós'', "hidden", and ''analýein'', "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems. Cryptanalysis is used to breach cryptographic se ...

. 5-UCO was fully synchronous, and therefore could be electrically regenerated on tandem high frequency (HF) radio links (i.e. one link connected to the next). It could operate directly with commercial circuits. The system also provided traffic-flow security (TFS). Another feature of the 5-UCO was that the receiving operator could maintain synchronisation if the path delay suddenly changed by "walking up and down" the key tape (one character at a time or one bit at a time). This procedure avoided the cumbersome task of a restart.Melville Klein, "Securing Record Communications: The TSEC/KW-26", 2003, NSA brochure, p. 4
(PDF)
/ref> 5-UCO required large amounts of key tape to operate on a continual basis. In 1960, supplying the key tape for a single 5-UCO in continuous use cost £5000 per year ()."Awards to civilian personnel in respect of cypher machine development", 1955-1960, PRO AVIA 65/977 In the US, the logistical problems involved in the generation, supply and destruction of sufficient quantities of key tape limited its use to only the most sensitive traffic. The Army Security Agency sought to develop a replacement, an effort later taken over by the newly formed

National Security Agency The National Security Agency (NSA) is an intelligence agency of the United States Department of Defense, under the authority of the director of national intelligence (DNI). The NSA is responsible for global monitoring, collection, and proces ...

and resulting in the fielding of the KW-26 (ROMULUS) system. Colonel G. Bellairs was awarded sums totalling £2250 for the development of 5-UCO, £750 in 1943, and £1,500 in 1960. Dr G. Timms and Mr D. C. Harwood were also awarded £1,000 for work on random tape for 5-UCO.

References

External links

5-UCO on Crypto Museum website
{{Cryptography navbox , machines Encryption devices

See also

References

External links