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Messages coded with simple substitution codes


The following message was created by a simple random substitution code:

“”ndyuji cjy yxndyuji kxnfxw vxkkcixk rkuji c lcfuxwo dh ndyuji vxwedyk, ncj ax c sdbxfhrt bco dh ujwfdyrnuji vuyytx cjy euie kneddt kwryxjwk wd ycwc ndttxnwudj cjy cjctokuk, jrvaxf wexdfo cjy ctixafc ctkd, ndyuji cjy yxndyuji cfx ujwfujkunctto ujwxfxkwuji wd kwryxjwk dh vdkw cixk, kd xjicixvxjw uk jdw rkrctto cj ukkrx hujyuji wuvx cjy kscnx uj wex nrffunrtrv vuiew ax vdfx dh cj ukkrx wexfx cfx kdvx lxfo iddy fxkdrfnxk cjy wxmwk wd rkx hdf ndyuji cjy yxndyuji kxnfxw vxkkcixk.””

That is, every letter of the alphabet was randomly replaced by a unique letter of the alphabet. This was not, therefore, a Caesar cipher.

This type of substitution code is susceptible to  decoding via frequency counts.

See if you can decode the message.

To make it a little easier I have preserved the word structure.

Note: Zach observed that I had not, originally, coded the capitalized letters, and he cracked the coded message pretty quickly using that and his prior experience in code breaking.

Here’s another, similarly coded message for you to crack:

“gqj zug qjm krj uqkz unr rzd fex gqp  ugfe jma euu yjn bad myj rmy and leu grs zqj jzm rgu qyr mya nqk jmk umr jzq jqe ean dle ugr rzd fex zqw uqa dmy jtd nqe erj fxu yjrj dlu qle ujd luc mys dnp myc dyj zua ndl eug buj rzd fex qes qbr kzq eeu ycu uwu yjz ugd rjq leu rjf xuy jrk euq neb gbt mnr jgu rrq cut qme uxm yjzu ruk dyx nur auk jlu kqf ruv qkz qnb sqr qle ujd knq kpm jmy nqa mxd nxu nzun umr qyd jzu ngu rrq cuj zun utd nut dnb dfj d qjj uga jjd knq kpf rmy cqt nui fuy kbq yqe brm r”

This time I made sure to put the message in lower case, removed punctuation, and then I split the coded message into blocks of 3 letters to destroy the word lengths.



  • I produced this coded message using Mathematica®, and the code of John McLoone at Breaking Secret Codes with Mathematica®
  • A free full cloud version of Mathematica®, with limited storage capability, is available at the Wolfram Development Platform (so schools and students do not need to purchase Mathematica® – they just need an internet connection).