substitution cipher. This device works by encrypting single plain letters

into two cipher symbols - in this case, the cipher symbols are the co-

ordinates of the Polybius Square.

Coords	1	2	3	4	5
1	A	B	C	D	E
2	F	G	H	I	K
3	L	M	N	O	P
4	Q	R	S	T	U
5	V	W	X	Y	Z

the plain text message: T H I S I S A S E C R E T M E S S A G E

the cipher text message: 44232443 2443 11 431513421544 32154343112215

the row and column [in that order] for each letter of the clear message -

however, the order is only important for this specific implementation. You could

grab the column first then the row. You could use any number, letter or symbol

in place of the columns and the letters of the alphabet could be in any order -

all these different methods simply add a layer of complexity [just as the Affine

Cipher did to the Caesar Cipher] but as a form of monoalphabetic

substitution cipher, they are all equally susceptible to cryptanalysis.

more difficult is the omission of the letter "J" [the letter omitted is just as

arbitrary]. Since both "I" and "J" will encrypt to "24", this can foil frequency

analysis [as well as my Multiliteral to Uniliteral Cipher Converter -although

the above encrypted message in particular would be properly converted since

both "I" and "J" do not appear in the message].