Vigenere Cipher: Description
Vigenere ciphers are simple poly-alphabetic ciphers derived
from Caesar ciphers.
Instead of shifting each plain text character by the same number,
as with a Caesar cipher, characters at different positions
might be shifted by different numbers.
Concretely, one picks an orderes n-Tuple of Caesar ciphers.
A character at position p in the plaintext is encrypted using
the (p mod n) + 1th cipher in the tuple.
For convenience one encodes such a tuple as a word by mapping
a Caesar cipher with shifting distance 1 to a, shifting distance 2
to b, and so on.
Vigenere ciphers form a group where the keylength of the product
of two vigenere ciphers is the lcm of the keylengths of the
Hence super-encipherment makes limited sense.
Equivalent Shifting Distance
13 5 18 3 5 4 5 19
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Breaking Vigenere Cipher
Vigenere ciphers are weak ciphers.
They can be broken by just looking at a
cipher-text and studying common bigrams and trigrams
in the cipher-text and their distance from each
In our approach we will concentrate on trigrams.
Last Update: 19.04.96 (Format: DD.MM.YY)