Some useful patterns in English

By about 1300 CE, Arabic cryptographers had determined that you can decipher messages in which one letter has been replaced by another letter, number, or symbol by exploiting statistical characteristics of the underlying language. Here are some especially useful patterns in English.

1. E is by far the most common letter – representing about 1/8th of normal text.
2. If you list the alphabet from most to least commonly used, it divides into four groups.
3. The highest frequency group includes: e, t, a, o, n, i, r, s, and h.
4. The middle frequency group includes: d, l, u, c, and m.
5. Less common are p, f, y, w, g, b, and v.
6. The lowest frequency group includes: j, k, q, x, and z.
7. E associates most widely with other letters: appearing before or after virtually all of them, in different circumstances.
8. Among combinations of a, i, and o io is the most common combination. Ia is the second most common. Ae is rarest.
9. 80% of the time, n is preceded by a vowel.
10. 90% of the time, h appears before vowels.
11. R tends to appear with vowels; s tends to appear with consonants.
12. The most common repeated letters are ss, ee, tt, ff, ll, mm and oo.

Naturally, there are thousands more such patterns. Even understanding a few can help in deciphering messages that have had a basic substitution cipher applied.

Here’s one to try out:

LKCLHQBCKDRCPQQBDKAPZULSQUCDK
AZRDTDGPCOTZKQDPQBZQDQZHHLOIP
XLSVDQBZAOCZQICZGLHQDJCQLOCZI
QBDKAPQBZQDKQCOCPQXLSDKXLSOPM
ZOCQDJCSKHLOQSKZQCGXLQQZVZDPO
CGZQDTCGXMLLOGXMOLTDICIHLOVDQ
BRZHCPQLLJZKXLHQBCJRGLPCNSDQC
CZOGXDKQBCCTCKDKA

One hint is that cipher alphabets are not always entirely random. The tools on this page are useful for cracking monoalphabetic substitution ciphers.

Author: Milan

In the spring of 2005, I graduated from the University of British Columbia with a degree in International Relations and a general focus in the area of environmental politics. In the fall of 2005, I began reading for an M.Phil in IR at Wadham College, Oxford. Outside school, I am very interested in photography, writing, and the outdoors. I am writing this blog to keep in touch with friends and family around the world, provide a more personal view of graduate student life in Oxford, and pass on some lessons I've learned here. View all posts by Milan