I have been reading the book "Serious Cryptography" by Aumasson to begin learning about Cryptography. There was a part where the author suggested how encryption using permutation should have these properties to be secured
- It should be a permutation, which is a rearrangement of the letters A to Z, such that each letter has a unique inverse. For example, a substitution that transforms the letters A, B, C, and D, respectively to C, A, D, and B is a permutation, because each letter maps onto another single letter. But a substitution that transforms A, B, C, D to D, A, A, C is not a permutation, because both B and C map onto A. With a permutation, each letter has exactly one inverse.
- The permutation should be determined by the key
- Different keys should result in different permutations.
- The permutation should look random
For the first property, I wonder if Vigenere Cipher can be considered to be secured (focusly based on the these permutation rules above) since certain keys can result in collisions.
Message = "ABBA" //
Key = "BA"
Ciphertext = "BBCA", with "A" and "B" having collided result.