11-01-2022, 09:20 PM
(This post was last modified: 11-01-2022, 09:22 PM by Mark Knowles.)
I think when considering ciphers there are some aspects which tend to be overlooked. I think a cipher needs to satisfy a few conditions:
1) It must be as hard as possible to decipher by someone without the cipher key.
2) It must be as easy as possible to encipher by someone with the cipher key.
3) It must be as easy as possible to decipher by someone with the cipher key.
4) The cipher key must be as easy to create as possible. I say this in the context of diplomatic ciphers where there is a different cipher key for each correspondent.
Obviously these different conditions tend to work against one another, so a balance has to be struck. Of these conditions 2, 3 and 4 are often overlooked.
In the context of diplomacy often the individuals applying the cipher such as envoys and ambassadors may not be skilled cryptographers, so conditions 2 and 3 are very important.
It is my hypothesis that we actually see a simplification of diplomatic ciphers in some Italian states during the latter part of the first half of the 15th century. This I think was in response to the realisation that ciphers that were getting increasingly complex had become too complicated to be practical for ordinary diplomats to use. This fits with my observation of some complex features found in earlier ciphers ceasing to be observed in later ciphers.
1) It must be as hard as possible to decipher by someone without the cipher key.
2) It must be as easy as possible to encipher by someone with the cipher key.
3) It must be as easy as possible to decipher by someone with the cipher key.
4) The cipher key must be as easy to create as possible. I say this in the context of diplomatic ciphers where there is a different cipher key for each correspondent.
Obviously these different conditions tend to work against one another, so a balance has to be struck. Of these conditions 2, 3 and 4 are often overlooked.
In the context of diplomacy often the individuals applying the cipher such as envoys and ambassadors may not be skilled cryptographers, so conditions 2 and 3 are very important.
It is my hypothesis that we actually see a simplification of diplomatic ciphers in some Italian states during the latter part of the first half of the 15th century. This I think was in response to the realisation that ciphers that were getting increasingly complex had become too complicated to be practical for ordinary diplomats to use. This fits with my observation of some complex features found in earlier ciphers ceasing to be observed in later ciphers.