Frequency analysis tools

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Frequency Analysis Tools

Both the pigpen and the Caesar cipher are types of monoalphabetic cipher. This means that each plaintext letter is encoded to the same cipher letter or symbol. For example, in the Caesar cipher, each �a� becomes a �d�, and each �d� becomes a �g�, and so on.
The main weakness of monoalphabetic ciphers is that although the letters themselves change, their frequency does not. So, any enthusiastic cryptographer could crack the code using frequency analysis tables of the original plaintext language. This method was first documented by an Arabic mathematician Abu al-Kindi in the 9th century.

Here are the percentages that the letters of the alphabet appear in English:

A	B	C	D	E	F	G	H	I	J	K	L	M
8.2	1.5	2.8	4.3	12.7	2.2	2.0	6.1	7.0	0.2	0.8	4.0	2.4
N	O	P	Q	R	S	T	U	V	W	X	Y	Z
6.7	7.5	1.9	0.1	6.0	6.3	9.1	2.8	1.0	2.4	0.2	2.0	0.1

If we put them in order of most frequent letter, it is easy to see that �e� is the most common letter, followed by the letter �t�:

E	T	A	O	I	N	S	H	R	D	L	U	C
12.7	9.1	8.2	7.5	7.0	6.7	6.3	6.1	6.0	4.3	4.0	2.8	2.8
M	W	F	Y	G	P	B	V	K	X	J	Q	Z
2.4	2.4	2.2	2.0	2.0	1.9	1.5	1.0	0.8	0.2	0.2	0.1	0.1

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