There are a lot of things I enjoy about puzzle caches. My favorites though are those that involve ciphers and codes. I am enthralled with the history and the intrigue of past plots involving code breaking. Some successes, such as Enigma, have helped end global atrocities. Others, like the Babington Plot, led to the downfall and eventual beheading of the Queen of Scotland. Some codes have allowed adolescent girls the ability to write in a diary keeping their secrets safe from the prying eyes of nosy sisters -- but that's a story for another time.
I know most cachers prefer cutting and pasting into cipher solvers, but I love trying to solve codes and ciphers by hand. I have spent hours and hours learning Morse Code solely for the purpose of puzzle caches.
Historical pen and paper ciphers used in the past are sometimes known as classical ciphers. They include simple substitution ciphers (such as Rot 13) and transposition ciphers (such as a Rail Fence Cipher). For example, "GOOD DOG" can be encrypted as "PLLX XLP" where "L" substitutes for "O", "P" for "G", and "X" for "D" in the message. Transposition of the letters "GOOD DOG" can result in "DGOGDOO". These simple ciphers and examples are relatively easy to crack.
Simple ciphers were replaced by polyalphabetic substitution ciphers (such as the Vigenère) which changed the substitution alphabet for every letter. For example, "GOOD DOG" can be encrypted as "PLSX TWF" where "L", "S", and "W" substitute for "O". With even a small amount of known or estimated plaintext, simple polyalphabetic substitution ciphers and letter transposition ciphers designed for pen and paper encryption are easy to crack.
During the early twentieth century, electro-mechanical machines were invented to do encryption and decryption using transposition, polyalphabetic substitution, and a kind of "additive" substitution. In rotor machines, several rotor disks provided polyalphabetic substitution, while plug boards provided another substitution. Keys were easily changed by changing the rotor disks and the plugboard wires. Although these encryption methods were more complex than previous schemes and required machines to encrypt and decrypt, other machines such as the British Bombe were invented to crack these encryption methods.
There are many, many different kinds of ciphers and codes. The Geocaching Toolbox has links to 20 different decryption sites. The first challenge is identifying what kind of cipher you're dealing with -- COs often leave clues on the cache page to nudge you in the right direction. The second challenge is ascertaining whether a keyword is required. If one is required, the key is often hiding in plain sight.
Have fun solving this cipher.
si ht on hn pf gg vf tf ku tf
ku ef od ng tl en pt ek od ln
ek gd fc en bs tp si ht on hn
pf nx gy ft hw ne vf ef od ng
tl en ix tb ns ii qg pf sf tb
tf qe go ia fc mm nl sf hf tz.
You can validate your puzzle solution with certitude.