Backstory
Crypto AG was a company located in Switzerland that specialized in communication security. They produced a number of encryption machines (some similar to the infamous Enigma) used for secure communication.
The company was secretly bought in 1970 by the CIA and the German intelligence agency BND. It has recently been revealed (11. February 2020) that the CIA & BND were responsible for installing backdoors in Crypto AG's machines (with knowledge of some high level Swiss state officials). The operation was first known by the code name "Thesaurus" and later "Rubicon".
Crypto AG was apparently a desirable target for it's neutrality as it is a Swiss company and because they sold products to over 120 governments (Iran, Argentinia, Italy, Vatican City, UNO, etc.), indifferent of political orientation.
Edit: Further information
Machines / designs that were definitely and intentionally compromised:
C52 / CX52, first manufactured in 1951
Many of the C-52 and CX-52 machines sold by Crypto AG were compromised to benefit the US and British national signals intelligence agencies, National Security Agency (NSA) and Government Communications Headquarters (GCHQ), respectively. (Wikipedia)
H460, first manufactured in 1967
In 1967, Crypto released the H-460, an all-electronic machine whose inner workings were designed by the NSA.
The warning proved prescient as Caflisch (American electrical engineer who applied and subsequently was hired by Crypto AG without knowledge of the American intelligence services) soon began probing the vulnerabilities of the company’s products. She and Spoerndli, a colleague in the research department, ran various tests and “plaintext attacks” on devices including a teletype model, the HC-570, that was built using Motorola technology, Spoerndli said in an interview.
[…]
“The algorithms,” he said, “always looked fishy.”
In the ensuing years, Caflisch continued to pose problems. At one point, she designed an algorithm so strong that NSA officials worried it would be unreadable. The design made its way into 50 HC-740 machines rolling off the factory floor before company executives discovered the development and stopped it. (Washington Post)
Machines / designs that were compromised with (so far) uncertain involvement of intelligence agencies (I have not yet found any reference other than Wikipedia mentioning these machines):
CD57, first manufactured in 1957
Sullivan shows how the CD57 can be attacked using a hill climbing search technique. (Wikipedia)
Questions
These backdoors (as others) could apparently be achieved on the basis of mathematical principles.
My questions are:
- How did the machines work?
- How exactly did the backdoors work?
