5-UCO

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The 5-UCO (abbreviated from 5-Unit Controlled , German: "Five units controlled"; also BID / 30 ) was a British key machine that used the cryptographically secure one-time key method ( English One-Time Pad , or OTP ) for encryption. used.

history

The machine was developed and used by the United Kingdom during the Second World War to equip its own teletype lines with the highest level of security against unauthorized decipherment . In particular, the intelligence information collected under the code name Ultra , which the British military was able to gain from the deciphering and analysis of the encrypted secret German communications, was forwarded in encrypted form using the 5-UCO .

After the war, around 1950, it was used for top-secret communication between the British and their American allies . It was later used in other British Commonwealth countries as well as within NATO . On the American side there was the SSM-33 based on the same principle (also called: SIGTOT ).

technology

Typical paper tape as the session key for 5-UCO was used
Baudot code

The 5-UCO worked on the principle of OTP and used as the support for the session key a hole strip of paper with the then usual number of five rows of holes (picture). Instead of a one-time pad (one-time block), a one-time tape ( one-time strip ), abbreviated as OTT , was actually used, but this does not change the cryptographically secure principle. The name 5-UCO comes from the number five of the rows of holes in this strip . In contrast to the Baudot code , which uses well-defined combinations of holes for character coding , the holes in the strip used as a key were punched as randomly as possible . This key was combined with the plain text data stream to be encrypted via an exclusive-or link (XOR) with the help of a mixer within the machine and resulted in the ciphertext as the output data stream .

For authorized decryption , an identically perforated strip had to be available on the receiver side as on the transmitter side. In order to maintain the full security of the procedure, each key-punched tape was only allowed to be used once and was then destroyed. This is a disadvantage of the method, which requires a complex and expensive key replenishment.

Also during the Second World War, the T43 telex key was used on the German side , which can be viewed as a cryptographic counterpart to the 5-UCO . In spite of their extremely high cryptographic security, the machines were only rarely used on both the German and British sides and only for extremely sensitive messages, as the required one-time key strips could not be produced and distributed quickly and cheaply in sufficient quantities.

literature

Web links

Individual evidence

  1. ↑ a b Ralph Erskine: The 1944 Naval BRUSA Agreement and its Aftermath , Cryptologia , 30: 1, 2006, p. 15, doi : 10.1080 / 01611190500401086
  2. ↑ 5-UCO in the Crypto Museum (English). Retrieved July 5, 2016.
  3. ↑ SSM-33 (SIGTOT) Cryptosystem on JProc.ca (English), accessed on August 9, 2019.
  4. ↑ 5-UCO at Jerry Proc (English). Retrieved July 5, 2016.