Cryptography Reference
In-Depth Information
The most frequent plaintext letter is assigned a value of 100 and the
remaining plaintext and ciphertext letters are given values from 0 to
100 relative to their frequency of occurrence. Thus, the most frequent
letter (1 on the horizontal scale) has a value of 100, while the next most
frequent letter (2) has a value of about 78, and so forth. The Vigenère
ciphertext has a remarkably less-telling distribution, although not as
pronounced as the completely flat random polyalphabetic cipher.
Encyclopædia Britannica, Inc.
The same would be true if digraph or trigraph fre-
quencies were plotted for a sufficiently long ciphertext.
In other words, the system is unconditionally secure, not
because of any failure on the part of the cryptanalyst to
find the right cryptanalytic technique but rather because
he is faced with an irresolvable number of choices for the
key or plaintext message.
