The A1Z26 cipher is a simple substitution cipher decoded by substituting the nth letter of the alphabet for given number n (and back again). Several other ciphers used in Gravity Falls work by applying this cipher first and then doing arithmetic - decryption is then done by reversing the arithmetic.
The Caesar cipher (or shift cipher) used in Gravity Falls uses a shift of +3 or -23: you encrypt by applying the A1Z26 cipher above, adding +3 or -23 using modular addition (so 1-3=25), and then undoing A1Z26 to get a letter. You decrypt by doing the same backwards, adding -3 or +23 (so A decrypts to X, for example).
The Atbash cipher works like the Caesar cipher, only instead of adding or subtracting 3 to letters 1-26, you apply A1Z26 with a numbering scheme of -13 to -1 and then 1 to 13 (skipping 0), then multiplying by -1. In other words, you simply mirror the alphabet.
In Journal 3, a symbol substitution cipher is used by The Author. The symbols are hidden on many pages of the journals. This cipher also encrypts some punctuation. The symbols for Q and Z used to be unknown, until the font CipherFontA was discovered from thisisnotawebsitedotcom.com.
A combined cipher is a mix of two or more ciphers seen in the show. The first time such cipher has been used is at the end of "Gideon Rises." It's solved by converting to letters using the A1Z26 cipher, then flipping the letters with the Atbash cipher, and finally by using the Caesar cipher. Season 2's combined ciphers start with the VigenĆØre cipher.
Combined cipher without VigenĆØre
Cryptogram
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Meaning
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Number codes[]
These codes are solvable by taking the number beside a parenthesis as an episode number, and the other numbers beside them represents a letter in that episode's credits cryptogram.
VigenĆØre cipher[]
VigenĆØre cipher is a series of Caesar ciphers where each letter shift depends on a key word. VigenĆØre ciphers use a VigenĆØre square, like the one below, to encrypt the message. The square is 26 rows of Caesar ciphers starting with a zero letter shift. On each additional row, the shift of the letters is increased by 1.
VigenĆØre cipher
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As VigenĆØre ciphers are a bit more complicated, consider the following example: we want to encrypt the message MABELEATSSPRINKLES and use GRAVITY as the key. We would repeat the key word until it matched the length of the message (in this case, GRAVITYGRAVITYGRAV). Using the table above, we match the message letter to a row and the corresponding key letter to a column and find the letter at their intersection on the table. For example, the row starting with M and the column starting with G intersect at S. The row starting with A and the column starting with R intersect at R. So using our message and the key, the we'd create the following cipher:
Message
MABELEATSSPRINKLES
Key
GRAVITYGRAVITYGRAV
Cipher
SRBZTXYZJSKZBLQCEN
Note that any time the message is A, the cipher letter will be the same as the key letter and vice versa.
Another way to think of VigenĆØre ciphers is that each letter of the key corresponds to a Caesar shift number (A=0, B=1, C=2, etc.) and for each letter of the message you form a Caesar shift based on the corresponding key letter.
In The Book of Bill, alongside several of the codes previously seen in the show and other material, there are also new codes introduced throughout the book. This cipher is primarily used in the Theraprism pages, but are also seen elsewhere in the book as a general-purpose alien writing.
Theraprism symbol substitution cipher
Cryptogram
Meaning
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Rune symbol substitution cipher[]
Another cipher introduced in The Book of Bill, this substitution cipher is made up of runes by the Vikings, originally put up as signs warning everyone to "throw Olaf overboard" if he ever tried to draw a triangle (representing Bill).
Rune symbol substitution cipher
Cryptogram
Meaning
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Alchemic symbol substitution cipher[]
Using the font 1651 Alchemy Symbols by GLC, this Book of Bill cipher appears sporadically throughout both the book and on the the tie-in website. It seems to be primarily used by Bill himself in a few rare occasions.
Alchemic symbol substitution cipher
Cryptogram
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Color substitution cipher[]
This substitution cipher, introduced in The Book of Bill, appears in some corners of The Book of Bill and in parts of the tie-in website.
Color substitution cipher
Cryptogram
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Bros.' Secret Code[]
This substitution cipher, created by Stan Pines and Ford Pines as kids, appears near the end of The Book of Bill and occasionally in the tie-in website.
THE PORTAL WHEN COMPLETED WILL OPEN A GATEWAY TO INFINITE NEW WORLDS AND HERALD A NEW ERA IN MANKINDāS UNDERSTANDING OF THE UNIVERSE. PLUS, IT WILL PROBABLY GET GIRLS TO START TALKING TO ME FINALLY.
The Caesar ciphers combined is a clue on how to solve the number code. Once decoded and put together, it reads "FROM THE FIRST UNTIL THE LAST / SEARCH THE CODES OF CREDITS PAST / ONE MEANS ONE SO SEARCH THEM ALL / WELCOME TO GRAVITY FALLS."
When the number codes are combined the message reads, "I WAS SO BLIND. HE LIED TO ME. THE DARKNESS IS NEAR."
IT STARTED WITH BAD DREAMS WHICH BECAME NIGHTMARES. I WAS FOOLISH, I WANTED ANSWERS, I PAINTED THE SYMBOLS, I SAID THE WORDS: WHEN GRAVITY FALLS AND THE EARTH BECOMES SKY FEAR THE BEAST WITH JUST ONE EYE.
S UPYTYH DIP GAVO QETHI MCBK OHK XEXJB VRW YOUWCHIA VRSV OQ LRDIA
A SIMPLE MAN WITH EAGER EARS MAY TRUST THE WHISPERS THAT HE HEARS
The cryptogram at the end of The Deep End is Spanish for "LONG LIVE THE POOL DUCKS"
Putting all the end frames from Season 2 together in a 3x7 format forms a picture of Stan and Ford, along with several Zodiac signs and a triangle behind them.
All end episode frames of Dipper's Guide to the Unexplained.
Putting all the end frames from Dipper's Guide to the Unexplained in a 3x2 format forms a picture of an eye with a red cross on it, foreshadowing the Society of the Blind Eye.
