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To make
cryptograms even easier to solve, test developers group
substituted letters with the words they came from, instead
of running everything together or breaking at an arbitrary
length. This allows attack by other means. For example,
A and I are the only single-letter words in
English. The most commonly occurring two-letter English
words, in decreasing frequency, are in,
on,
an,
he, to,
and
or.
Most
substitution ciphers can be quickly broken by frequency
analysis. The six most commonly occurring letters in
ordinary English text, in decreasing frequency, are E T
A O I N, a pattern easily remembered as
E Tao In. The
most frequently occurring ciphertext letter normally
corresponds to E, the next to T, and so forth, cascading
down to N. |
