# Replacement Cipher

Replacement cipher: Let τ be a permutation of the alphabet, and apply τ to each letter of the message. Frequency analysis is useful for breaking this type of code. Decode the following, which was encoded using a replacement cipher.

MIZVN KXXHA XRRTK NXYEX QIZVI IZXWM NXYGT JWVHC YTOXX QNHTI JYTWV NMHUR XOYLN ZTJTE XYAZX RWMHU XEMRK LIJYT WNWVR REXPV IMTHN OTHIM HLVRR GYXCX VIXQ --- NVWLX RBTZH NTH

I have made a frequency table of the occurrence of each letter in the above code.

X-18 T-12 H-10 N-10 R-10 I-9 V-9 Y-8 M-7 W-7 Z-6 E-4 J-4 L-4 K-3 O-3 Q-3 A-2 C-2 G-2 U-2 B-1 P-1 D-0 F-0 S-0

Comparing this with the frequency of letters occurring in English leads me to believe that X corresponds with E and that T corresponds with T. However this is where I get stuck.

• Note that the words are in groups of five letters, except for the last words. I don't know of any language with mostly five-letter words, so it seems that the spacings in between the words have been changed. Also, it seems to be a quote. The last three words is most likely the name of a person. – Joel Reyes Noche Nov 21 '14 at 1:26
• @Amzoti - using the frequencies in English, replacing letters based on that alone does not yield any clear text. – UserX Nov 21 '14 at 1:27
• @JoelReyesNoche - I saw that too; unfortunately that didn't help me when trying to replace letters. – UserX Nov 21 '14 at 1:27
• Look at the double letters (XX, RR). Do you know the frequencies of double letters in English? (I expect EE, OO would be the highest). – Joel Reyes Noche Nov 21 '14 at 1:31
• This is problem 5.2 of Survey of Mathematical Problems, which is in English, so the text is also most likely in English. – Joel Reyes Noche Nov 21 '14 at 1:39