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I am researching how quantum computers affect current encryption methods (RSA and more). However, I remember learning in a course that there used to be a particular encryption method which was popular but suddenly had a very bad vulnerability in the past (like quantum computers and Shor's algorithm would be for RSA) and everybody had to move on (is that right?). I cannot find anything about this in the past, does anybody have any idea which cryptosystem I am talking about? |
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You could be thinking about the Merkle-Hellman knapsack cryptosystem. It was invented in 1978 and everything seemed well and good until it was completely broken six years later in 1984 by Shamir - it was a complete and total break, i.e. the cryptosystem became unusable overnight. That said I don't know if the knapsack cryptosystem was ever "popular" in the modern sense (it was 1978 after all) but it was certainly an early public key cryptosystem that met an unfortunate end. On the other hand, for an example of a progressively worn-down algorithm (as opposed to one being broken immediately) there is of course MD5's collision resistance. |
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This is a shot in the dark, but could you be thinking of the Needham-Schroeder protocol? It was published in 1978 [1], and an attack was published as much as 18 years later, in 1996 [2]. It is not an encryption method, though, but a protocol. In fact, the original paper does not even specify an encryption method to be used, but uses encryption symbolically. Accordingly, the discovered flaw has nothing to do with encryption; rather, it is a conceptual flaw in the protocol's design. However, it is often used in cryptography/security courses as a historical example of a protocol broken late after its invention, so I thought you might have been thinking of this one. Another popular example that comes to mind is WEP, a link-layer security protocol which was part of the original IEEE 802.11 specification from 1997 and the predecessor of WPA/WPA2. This one was broken due to cryptographic breaches resulting from various weaknesses in its design and misapplications of cryptographic primitives [3,4].
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