Strategies for Deciphering



The first things you should do is

get organized!

Compile a list of known codes and cipher methodologies that you can use on secret messages. Once you have tried all the methods you know of, use a hit and miss method, trial and error. The structure of the English language enables cryptologists to see patterns that emerge from normal messages. Just by looking at this paragraph of text, or playing Wheel of Fortune, you can figure out which letters are most common.

Vowels and spaces are the most frequent in the English language. A few constants, such as "S, T, N, etc." are more common than others. Finally, a few known bigrams (2 letters), such as "ll, ee, ss, etc," are more common than others. By recognizing patterns in ciphers you can often guess what the letters are decipher the message. The computer application "Cryptogrammer" teaches you how to decipher this way. Ask your instructor if you are interested in playing Cryptogrammer.

Most Common Letters

In order of most comon to least common:
1. E
2. T
3. A, O, N, R, I, S
4. H
5. D, L, F, C, M, U
6. G, Y, P, W, B
7. V, K, X, J, Q, Z

Bigram Frequency

In order from most common to least common:
TH, HE, AN, RE, ER, IN, ON, AT, ND, ST, ES, EN, OF, TE

Bigram Same Letter Frequency

In order frommost common to least common:
LL, EE, SS, OO, TT, FF, RR, NN, PP, CC, MM, GG

Trigram Frequency

THE, ING, CON, ENT, ERE, ERS, EVE, FOR, HER, TED, TER, TIO, VER

Intial Letters

T, A, O, M, H, W, C, I, P, B, E, S

Second Letters

H, O, E, I, A, U, N, R, T

Third Letters
E, S, A, R, N, I

Final Letters
E, T, S, D, N, R, Y, G

*More than 50% of English words end with "E."
*More than 50% of English words start with T, A, O, S, or W.

Frequency Tables for Deciphering


It's a good idea to

create a table of the counts

for letters of the alphabet, bigrams, trigrams, and initial and ending letters to see how many times a certain letter(s), number(s), or symbol(s) from an encrypted message occurs. The highest occurance of a single letter/number/symbol is most likely to be "E" as seen in the frequency table above. The most common 2 letter/number/symbol bigram is likely to be "TH." If you can place a few likely letters you will often see a few short words, like "THE" appear.

Once words start to appear you're on to something. See if there is an easy pattern to get the rest of the letters. If not, continue

analyzing frequency tables

to decode the rest of the letters.

Use trial and error

and replace letters/numbers/symbols with different letters until more words begin to appear. Try this method on the simple cipher below. Can you figure out what the encrypted message says?


Wpxfmt bsf uif nptu dpnnpo mfuufs