One of the most common non-computerized forms of cyptography is the classic substitution cipher, in which the encryption is based on one letter being replaced by another in the alphabet, such as "A = R, B = Y", etc.
Note that throughout this tutorial, I will capitalized all solved letters in the expression.
You will need:
- An online letter positioning dictionary (a dictionary that searches words depending on the positions of letters. Often used for crosswords)
- A piece of paper or a Word Document
Let's say we have this particular message we want to decode:
Hgz etei, hwx'k ry awrqa? R'i fseqqrqa yw aw yw e fepyz!
1. The easiest letter by far to find is "A". The only non-capitalized uniletter word in the English language is the designative "a" as in "a person". (yes, I know, "I" is another one, but its always capitalized) We see that there is one instance where this occurs. The letter e in this cipher is alone and uncapitalized. Therfore e = a.
We now get this:
Hgz atai, hwx'k ry awrqa? R'i fsaqqrqa yw aw yw a fapyz!
2. Now, let's look at the term "R'i". We know that the only two letters split by an apostrophe in the english language are "I'd" and "I'm". Knowing that "I" always comes first in this expression, we notice r = i
We then get this
Hgz atai, hwx'k ry awrqa? I'i fs aqqrqa yw aw yw a fapyz!
3. Before solving the rest of the "R'i", let's look a the term "hwx'l". The only word except for capitalized business names (Roe's, Lay's, etc.) is "how's"
We then come do the following letters
hwk'l = how's
h = h w = o k = w l = s
Put it into the sentence:
Hgz atai, how's ry aorqa? I'i fsaqqrqa yo ao yo a fapyz!
4. The term "fseqqrqa" seems to be a long word, don't you think? Actually, only adverbs are longer than 7 letters. All adverbs end in "ing". Thus
fseqq(rqa) ------> rqa = ing
r = i q = n a = g l = s
Hgz atai, how's ry aorqa? I'i fsanning' yo ao yo a fapyz!
Two words end in "anning": Planning and Scanning. I'd planning and I'd scanning don't work, therefore the expression searched is "I'm"
So, i = m
Hgz Adam, how's ry'aorqa? I'm planning to go to a fapyz!
(Note: The only two-letter expression to come before "go" in the english language is to, therfore y = t. "I'm scanning to go to" doesnt work, so were left with "I'm planning)
5. Expression hgz
The only two words in the English language to have h as a first letter and have two others are "hey" and "hit"
"Hit Adam, how's..." would require how's to be the first word of a sentence, therfore the first word is "hey", and therfore g = e and z = y
Hey Adam, how's it going? I'm planning to go to a fapyy!
6. Expression fapyy
Going through a good ol' online letter positioning dictionary, we find the only word to have a as its second and y as its last letter without having the same third and fourth letter (that would be "sappy") is "party". Therefore, as the final sentence, we have:
Hey Adam, how's it going? I'm planning to go to a party!
And that's how you solve a substitution puzzle!
Adapted from a deleted RationalWiki article by RationalWiki user AgnosticoRationale