사용자:Bjh13579/SIGABA
위키백과 ― 우리 모두의 백과사전.
ECM Mark II는 미국이 제 2차 세계대전에서 1950년대까지 사용한 에니그마와 유사한 암호기계이다. 이 기계는 육군에서는 SIGABA 혹은 Converter M-134로 불려졌고, 해군에서는 CSP-888/889로 불려졌으며, 해군 판으로 수정된 CSP-2900이 있다.
그 시대의 많은 암호기계들처럼 SIGABA도 전자 로터로 메시지가 암호화 되었고, 로터의 배열이나, 기계의 작동 방식같은 암호해독법이 없으면, 암호를 푸는데 평생을 보내야 할 정도 였다.
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[편집] 역사
SIGABA는 미국 암호제조자들이 It was clear to US cryptographers well before WWII that the single-stepping mechanical motion of rotor machines (e.g. the Hebern machine) could be exploited by attackers. William Friedman, director of the US Army's Signals Intelligence Service, devised a system to correct for this by randomizing the motion of the rotors. His modification consisted of a paper tape reader from a teletype machine attached to a small device with metal "feelers" positioned to pass electricity through the holes. For any given letter pressed on the keyboard, not only would the machine scramble the letters in a fashion largely identical to other rotor machines, but any holes in the tape at that location would advance the corresponding rotors, before the tape itself was advanced one location. The resulting design went into limited production as the M-134, and its message settings included the position of the tape and the settings of a plugboard that indicated which line of holes on the tape controlled which rotors. However, there were problems using fragile paper tapes under field conditions.
Friedman's associate, Frank Rowlett, then came up with a different way to advance the rotors, using another set of rotors. In Rowlett's design each rotor must be constructed such that between one and four output signals were generated, advancing one or more of the rotors.
There was little money for encryption development in the US before the war, so Friedman and Rowlett built a series of "add on" devices called the SIGGOO (or M-229) that were used with the existing M-134s in place of the paper tape reader. These were external boxes containing a three rotor setup in which five of the inputs were live, as if someone had pressed five keys at the same time on an Enigma, and the outputs were "gathered up" into five groups as well — that is all the letters from A to E would be wired together for instance. That way the five signals on the input side would be randomized through the rotors, and come out the far side with power in one of five lines. Now the movement of the rotors could be controlled with a day code, and the paper tape was eliminated. They referred to the combination of machines as the M-134-C.
In 1935 they showed their work to a US Navy cryptographer in OP-20-G, Wenger. He found little interest for it in the Navy until early 1937, when he showed it to Commander Laurance Safford, Friedman's counterpart in the Navy's Office of Naval Intelligence. He immediately saw the potential of the machine, and he and Cmdr. Seiler then added a number of features to make the machine easier to build, resulting in the Electric Code Machine Mark II (or ECM Mark II), which the Navy then produced as the CSP-889 (or 888).
Oddly the Army was unaware of either the changes or the mass production of the system, but were "let in" on the secret in early 1940. In 1941 the Army and Navy joined in a joint cryptographic system, based on the machine. The Army then started using it as the SIGABA.
[편집] SIGABA에 대한묘사
SIGABA는 여러 로터들이 평문을 다른 글자로 바꾸는 것을 이용하는 에니그마와 비슷한 이론을 가졌다. 에니그마와 다른점은 에니그마는 로터를 3개(반사 바퀴를 제외)를 쓰는데 비해서, SIGABA는 반사바퀴를 사용하지 않고, 15개의 로터를 이용했다.
The SIGABA had three banks of five rotors each; the action of two of the banks controlled the stepping of the third.
- The main bank of five rotors was termed the cipher rotors, and each had 26 contacts. This acted similarly to other rotor machines, such as the Enigma; when a plaintext letter was input, a signal would enter one side of the bank and exit the other, denoting the ciphertext letter.
- The second bank of five rotors was termed the control rotors. These were also 26 contact-rotors. The control rotors received four signals at each step. After passing through the control rotors, the outputs were divided into ten groups of various sizes, ranging from 1–6 wires. Each group corresponded to an input wire for the next bank of rotors.
- The third bank of rotors was called the index rotors. These rotors were smaller with only ten contacts, and did not step during the encryption. After travelling though the index rotors, one to four of five output lines would have power. These then turned the cypher rotors.
The SIGABA advanced one or more of its main rotors in a complex, pseudorandom fashion. This meant that attacks which could break other rotor machines with more simple stepping (for example, Enigma) were made much more complex. Even with the plaintext in hand, there are so many potential inputs to the encryption that it is difficult to work out the settings.
On the downside, the SIGABA was also large, heavy, expensive, difficult to operate, mechanically complex and fragile. It was nowhere near as practical a device as the Enigma, which was smaller and lighter than the radios it was used with. It found widespread use in the radio rooms of the US Navy's ships, but as a result of these practical problems the SIGABA simply couldn't be used in the field, and, in most theatres other systems were used instead, especially for tactical communications. The most famous may be the Navajo wind talkers who provided tactical field communications in parts of the Pacific Theater beginning at Guadalcanal. In other theatres, less secure, but smaller lighter and tougher machines were used. SIGABA, impressive as it was, was overkill for tactical communications.
[편집] Combined cipher machine
SIGABA was also adapted for interoperation with a modified British machine, Typex. The common machine was known as the Combined Cipher Machine (CCM), and was used from November 1943.
