Here’s a puzzle cache, just to switch up the scene a little with a good old cryptographic challenge. The cache is not at the published coordinates, as you need to crack the code below to figure out where the cache is hidden.
Some Historic Background
This cache is a nod to the history of the area. This place was once RAF Chia Keng, a British Royal Air Force Military Base which served as a base for the Government Communications Headquarters (GCHQ) in Singapore. The GCHQ started off as the Government Code and Cypher School (GC&CS), which, as the name suggests, specialised in cryptography and code-breaking, and included feats like breaking the Enigma Cipher during World War II at Bletchley Park.
The GCHQ’s first listening station for the Far East was located here at RAF Chia Keng, and one can only wonder about what top secret communiques were picked up by the aerial masts that once stood tall in the vicinity. And so, in the spirit of the history of the place, it is only apt that a cryptic puzzle be placed here to challenge you.
The Simple Substitution Cipher
Substitution ciphers are probably the oldest form of cryptography, simply because the idea behind it is well… simple. Every letter in the alphabet undergoes a one-to-one substitution with another letter, thus obscuring the message by means of a “function” known only to the sender and the receiver. The substitution function or key is fixed throughout the entire encoding process, which is in contrast to more complex ciphers, like the polyalphabetic cipher, where each letter can be enciphered to various other letters depending on its position in the plaintext and another secret keyword.
Of course, the simplicity of the cipher also means that it is easily broken through various means. The most well-known illustration of how substitution ciphers can be broken "by hand" was deftly written as a plot point in Sir Arthur Conan Doyle’s “The Adventure of the Dancing Men”, in which Sherlock Holmes used a number of classic methods to crack the code. These methods were frequency analysis (i.e. using the frequency of common letters in words of a language), and the use of common bigrams and trigrams (i.e. two letter or three-letter sets that frequently appear in a language).
However, the difficulty of a code using the substitution cipher could be increased by chunking the letters into regular blocks (usually of 5 letters) to obscure the presence of short and common one, two or three letter blocks in a text (e.g. "an", "the", "to" and the like) hence making it a little harder to identify these blocks. But, which a sharp eye and nowadays, using computers and programmes, the frequency of letters and N-grams can still easily be tabulated in spite of this. Adding in algorithm that uses a dictionary attack and scanning the resulting plaintext for recognisable words further hastens the rate at which these codes can be broken.
Cracking substitution ciphers can be still further “complicated” by adding in deliberate misspellings in the plain text and the use of the other languages to throw off such programmes that are built to function in a particular language, but even then, with enough perseverance, a large enough dataset and some good observational skills, the combination of a human and computer scanning through the possibilities should be able to crack the vast majority of substitution ciphers.
With all that said, why not try your hand at this puzzle and see if you can really crack my “simple” substitution cipher?
The Puzzle
Before we begin, let me outline a few key parameters that are absolutely true about the substitution cipher key I am using for this puzzle.
- The plaintext is indeed in English. In fact, I am going to further divulge that it is in Standard British English.
- This is a “simple” substitution cipher, that is, every character in the ciphertext decodes to exactly one and the same character in the plaintext throughout the whole message.
- There are no other types of ciphers used, that is, no transposition (i.e. scrambling of the letter positions), polygraphic (i.e. one plaintext character represented by more than one ciphertext character) or polyalphabetic (i.e. any character being possibly encoded to all other characters) cipher shenanigans going on in this puzzle.
- There is, however, a non-cryptographic additional “layer” in the puzzle which you need to figure out, and it is not because I deliberately misspelt any of the plaintext words.
To make things even simpler, I will even give you two pangrams (i.e. sentences that contains all the letters of the English alphabet) and their corresponding ciphertexts encoded using my substitution cipher. This would render cracking most substitution ciphers trivial, as I hope it would for you in this case, too (see, I am not all that evil).
Plaintext: “THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG”
Ciphertext: PHCIB CWMÏQ SLNCA TUÉOG AHQRH PHKÇB FETNY
Plaintext: “TOM SHALL PACK MY BOX WITH FIVE DOZEN LIQUOR JUGS”
Ciphertext: DNOÜX KGXCO ÏBWNC AIBPL ÏBRTÉ FHSKB CHTUÉ YF
And finally… your challenge:
Puzzle Ciphertext: ABDE BS IBDÜ PH BSDHMSXÜHSK LHQSJDBC HAHQABÇBÜHS INF BADXWKBÜD
Input the answer to the question in the plaintext into Certitude to get the final coordinates:
Good luck!