The Codex image was posted early on in the game and has been used to solve various puzzles.
The image was originally posted by Adam on his blog. He claims to have received it from a stranger from the future, who indicated "You will be in need of this soon". The image includes all letters of the alphabet and the digits 0-9 arranged in a 6x6 square.
The first form of encoding that uses this image involves a 'knight move' from chess. Given a letter to be encoded, and its position on the Codex image, the knight move can lead to 8 positions on the image (at most). For instance, from the letter 'P', we could reach the following letters/digits: H, C, E, L, X, 2, 0 (zero), T. Which of these paths should be followed when encoding a letter depends on the quadrant of the image that the letter to be encoded lies on.
The image to the right highlights the quadrants, and illustrates the 4 paths to be followed:
- Top-Left Quadrant: encode by moving Right, Right, Down (e.g.: A encodes to I, O encodes to W);
- Top-Right Quadrant: encode by moving Down, Down, Left (e.g.: D encodes to O, P encodes to 0 (zero) );
- Bottom-Right Quadrant: encode by moving Left, Left, Up (e.g.: V encodes to N, 9 encodes to 1);
- Bottom-Left Quadrant: encode by moving Up, Up, Right (e.g.: S encodes to H, 6 encodes to V).
Note that, while moving from one quadrant to the next in a clock-wise fashion, the paths to be used in encoding a letter follow from each other (i.e.: move twice in the last direction you moved when encoding in the previous quadrant, then turn 'right' and move once), creating a pattern of their own (a square).
The whole set of encoding is as follows:
Multiple clear letters encode to the same encoded letter (e.g.: both E and H encode into P); this makes the decoding process a bit of a guess-work in some aspects. Spaces between words help the decoding process since they make it possible to guess some of the letters or words; the sentence structure helps in resolving any remaining ambiguity.
At least in one case, when this system was used to encode a message, some inconsistencies were introduced. See Going Places Puzzle - Sabotage for details.
A second encoding used in conjunction qith the Codex image involves representing each letter in the message as a 2-digits number RC, where the first digit R is the row (in the image) where the letter is found, and the second digit C is the column where the letter is found. Rows and columns are numbered 1 through 6. Thus the whole set of encodings is as follows:
clear : H e l l o W o r l d encoded: 22,15,26,26,33 45,33,36,26,14
Decoding a message encoded with this system is a simple matter.