Cipher Bronze Mystery Cache
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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.
Multilateral Substitution Ciphers
The first cipher we looked at was the simple substitution cipher. In this case the letters of plaintext are replaced with another letter.
The problem with these is that frequency analysis can quickly lead to the cipher being broken. To avoid this the cipher text needs to ensure that more than one symbol of cipher represents one letter of plaintext. One method is to use multiple ciphers in sequence on the plaintext, first one cipher on one letter, then another cipher on the next etc. and then repeat the sequence again.
We will come across this type of cipher later in the series but for now we will introduce a small change than makes cracking at bit harder. Rather than one letter being converted into one cipher letter, number or symbol we will convert it into 2 (or more) letters, numbers or symbols.
In the diagram below the plaintext letters are in the centre and the ciphertext in on the outside.
Looking at this we can see that 'g' becomes 'gb', 'o' becomes 'hd' etc.
However this is still a monoliteral system and can easily be cracked once recognised.
To improve this some of the first and second letters can be the same.
In this case 'g' becomes 'bb' and 'o' becomes 'cd'. Example:
p:the cache is under a rock
c:ddbcae acaaacbcae bddc deccadaedb aa dbcdacbe
or if we loose the structure of the words
c:ddbca eacaa acbca ebddc decca daedb aadbc dacbe
There are now only 5 letters encoding the alphabet!
Cracking Multiliteral Substitution Ciphers
This may now seem a daunting task but all is not lost. Given just the ciphertext the number of letters,numbers or digits can be counted. If there is suspicion of this being an multiliteral substitution cipher then certain things may become apparent such as an even number of characters and certain letters,numbers or codes only appearing every so often. This can clearly be seen in the first example above.
The distribution of digraphs will also follow the usual pattern so in the second sample the pair 'ae', which represents the letter 'e', will be more common than 'be' which represents the letter 'k'.
At this stage a Phi Test can be made to determine if the distribution is suitable and then an standard substitution attack performed.
For further details and examples refer to FM34-40-02.
The Cipher for the "Cipher Bronze" location is:
4 2 1 4 1 2 4 8 5 4 2 2 3 6 2 0 2 8 3 4 2 0 3 8 2
6 1 2 1 4 2 2 2 6 1 6 2 0 2 2 1 2 4 8 3 2 2 0 4 2
2 2 3 8 4 0 4 6 3 4 4 6 4 8 3 2 2 0 5 2 2 2 4 8 2
0 1 2 4 6 3 4 3 0 1 6 2 2 1 6 2 6 2 2 3 2 5 0 3 0
2 0 3 0 3 8 1 4 1 0 2 0 3 8 1 4 1 4 3 6 3 2 3 4 3
0 3 2 1 4 1 6 1 6 1 4 1 2 4 8 3 2 4 6 5 0 4 2 4 2
1 4 1 2 4 8
Many muggles pass by this location although you will find you are quite invisible when next to the cache!
Additional Hints
(Decrypt)
Gur HF Nezl vf lbhe sevraq.
Treasures
You'll collect a digital Treasure from one of these collections when you find and log this geocache:
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