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Difficulty:
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Terrain:
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Size: 
(micro)
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Introduction
The "Metal Cipher" series of geocaches is designed to give experience in hand solving simple ciphers. All the caches will be micro and attached to, or in, man-made structures to give some physical challenge.
The initial series will include tin(GCZ1C6), bronze(GCZ4FB), silver(GCZA96) and gold (GCZK1E) and will represent ciphers of increasing difficulty and are best attempted in order.
Ciphers vs. Codes?
A cipher is different from a code in that the units in a plaintext, usually the letters, are swapped with another unit. This is different from a code where an entire word, phrase of concept is replaced with a number, letter or symbol of some sort.
Example
Plaintext: The cache is located under a rock about ten metres south east of the large tree.
Cipher: EFQ OXOFQ ZV PSOXEQG TDGQY XYSOL XCSTE EQD UQEYQV VSTEF QXVE SM EFQ PXYWQ EYQQ
Code: 23 45 73 125 88 23 32 143 87 321 11 98 33 23 532 222
Substitution Ciphers
The first cipher we will be looking at is the simple substitution cipher. In this case the letters of plaintext are replaced with another letter.
An example we all use is the method used for hiding clues with caches, where pairs of letters are swapped. The specific one used on the gc.com website is called ROT13.
Example 1: ROT13
Plaintext :a b c d e f g h i j k l m n o p q r s t u v w x y z
Ciphertext:n o p q r s t u v w x y z a b c d e f g h i j k l m
Here we have just shifted the ciphertext by 13 characters.
Example 2:With Codeword "Cipher Tin" refered to as a "keyword mixed sequence"
Plaintext :a b c d e f g h i j k l m n o p q r s t u v w x y z
Ciphertext:c i p h e r t n a b d f g j k l m o q s u v w x y z
When using a codeword the unique letters of the codeword are spelled out first, then the unused letters.
Example 3: Random
Plaintext :a b c d e f g h i j k l m n o p q r s t u v w x y z
Ciphertext:V D Y H G R Q J N S M F P O X C U L T I K W Z A B E
The letters here have been randomly assigned.
Cracking substitution ciphers
The basic method to cracking these ciphers is as follows:
Convert any symbols to letters a-z and check no more than 26 different symbols or 36 including digits.
Perform a frequency analysis on the ciphertext looking for the expected pattern but shifted as in a Caesar Cipher. Also look to see if it is reversed.
If no obvious pattern that matches a plaintext distribution then assume a random cipher or polyalphabetic.
Perform a Phi Test to check that Phi is between 1.5 and 2.0 (see FM34-40-2)
Most likely a simple substitution if in this range, else a polyalphabetic cipher or worse.
Looking at frequency analysis check most common letters, digraphs, three letter words etc. (see below)
The Cipher for the "Cipher Tin" location is:
THKPLO SHG TMG EL CJUGA UGALO SPL TLGSLO ELMF JG SPL SOUQQ QHX TPMHGQ LMQS
I would strongly suggest tackling the final location at night as many muggles pass by and you will be in plain sight. Furthermore it might be wise to tackle this with a friend due to the terrain.
Online tools
Google FM34-40-2 and download for a free copy
There are various tools that can be found online for performing a frequency analysis.
Order Of Frequency Of Single Letters
E T A O I N S H R D L U
Order Of Frequency Of Digraphs
th er on an re he in ed nd ha at en es of or nt ea ti to it st io le is ou ar as de rt ve
Order Of Frequency Of Trigraphs
the and tha ent ion tio for nde has nce edt tis oft sth men
Order Of Frequency Of Most Common Doubles
ss ee tt ff ll mm oo
Order Of Frequency Of Initial Letters
T O A W B C D S F M R H I Y E G L N P U J K
Order Of Frequency Of Final Letters
E S T D N R Y F L O G H A K M P U W
One-Letter Words
a, I.
Most Frequent Two-Letter Words
of, to, in, it, is, be, as, at, so, we, he, by, or, on, do, if, me, my, up, an, go, no, us, am
Most Frequent Three-Letter Words
the, and, for, are, but, not, you, all, any, can, had, her, was, one, our, out, day, get, has, him, his, how, man, new, now, old, see, two, way, who, boy, did, its, let, put, say, she, too, use
Most Frequent Four-Letter Words
that, with, have, this, will, your, from, they, know, want, been, good, much, some, time
Additional Hints
(Decrypt)
Guvf vf n EBG13 pvcure