The security measures at 8:35 You say that the keys can only be used once? Does that mean the message can’t be decrypted? Or it would be entirely 1,000x harder to figure out without the key, which obviously makes sense.
No, the keys can be used as often as you like. But that would be not a good idea. The security can be increased massively, when every message has its own secret key. But that requires the exchange of many keys between the two communication partners in advance. During WWII, the Lorenz cipher was broken, because the identical key setting was used twice for two messages that weren't the same. Using the same key more than once, offers more possibilities to analyze and break the key.
The Kasiski test was first published in 1863, but it was known and used long before that. Charles Babbage's private notebooks lay out his use of this method in 1846. How long this method had been known, and how widely, we cannot know. Nor whether it was passed secretly or rediscovered multiple times.
The security measures at 8:35
You say that the keys can only be used once? Does that mean the message can’t be decrypted? Or it would be entirely 1,000x harder to figure out without the key, which obviously makes sense.
No, the keys can be used as often as you like. But that would be not a good idea. The security can be increased massively, when every message has its own secret key. But that requires the exchange of many keys between the two communication partners in advance. During WWII, the Lorenz cipher was broken, because the identical key setting was used twice for two messages that weren't the same. Using the same key more than once, offers more possibilities to analyze and break the key.
The Kasiski test was first published in 1863, but it was known and used long before that. Charles Babbage's private notebooks lay out his use of this method in 1846. How long this method had been known, and how widely, we cannot know. Nor whether it was passed secretly or rediscovered multiple times.
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