Blog Description



This blog is a personal examination of the "Pizza Code Mystery" ARG created by Christopher Horn for the Black Mesa video game.
I will attempt to update this blog on a regular basis, for as long as the ARG is in existence and folks are willing to attempt to solve it.
This will not be a complete overview of the clues and such associated with the ARG--you can find a complete, up-to-date version of that material here.


Cipher Descriptions

The purpose of this page is to compile the data about possible ARG-related ciphers, mainly those that may come into play later.  Furthermore, I intend to break down the ciphers into easy-to-understand language and to provide key points to those that need a "refresher course" on the main outline of each cipher.

The Straddling Checkerboard Cipher

Description
The straddling checkerboard is most commonly constructed of a 10 x 3 table that is completed with all of the letters of the alphabet and four blank spaces (two of which are utilized as "space markers" in the first row, and two of which block off the end of the table).  The table's columns are headed by the numbers 0-9 and the table's second and third rows are identified by whatever numbers have spaces affixed to them.

The table's first row should contain eight letters--to allow for two spaces--and the rest of the table should be completed with the remaining 18 letters, except for the last two spaces which would be left blank.  These first eight letters can be any letters, but they are often composed of the eight most commonly used letters in the English alphabet:  E, T, A, O, I, N, S, R [some sources list "H" as the eighth most common letter, followed by R].  Furthermore, one common "key" first row is "AT ONE SIR".  However, it is important to stress that this first row can be composed of any letters, despite common conventions.

Step-By-Step
Below is an example of a straddling checkerboard, as well as the steps taken to complete it:
  1. Start with an 8-letter keyword, key phrase, or random combination.  These can include any letters, but a variation on the letters E, T, A, O, I, N, S, R (H) is most common.  You can also use a phrase that reuses letters, but you will only use the first instance of each letter.  Leave two blanks within your choice.  For this example, I will use: 

    _ION_STARE

  2. Next, fill in the column header with the numbers 0-9.  These can also be in any order, but they are generally kept in either ascending or descending order--0 can also be the number before 1 or after 9, depending on choice.  I will use 0-9 in ascending order:

    0   1   2   3   4   5   6   7   8   9
     3. Then, fill in the eight letters you chose, including spaces, underneath the numbers you chose:
0
1
2
3
4
5
6
7
8
9

-
I
O
N
-
S
T
A
R
E























     4. You will then fill in the second and last row headings with the two numbers that have
         corresponding blank spaces--in this example, those numbers are 0 and 4:
0
1
2
3
4
5
6
7
8
9

-
I
O
N
-
S
T
A
R
E
0










4











     5.  Then, fill in the rest of the letters in the alphabet in order, leaving the last two spaces of the
          table blank:
0
1
2
3
4
5
6
7
8
9

-
I
O
N
-
S
T
A
R
E
0
B
C
D
F
G
H
J
K
L
M
4
P
Q
U
V
W
X
Y
Z
-
-

     6.  Now that you have your straddling checkerboard, all that is left is to supplement the numbers
          throughout the cipher with the numbers in the checkerboard.  When you come across a 0 or a 4,
          start at that row and stop at the letter underneath the number that corresponds with the number
          after the 0 or 4.  E.g. 05 = H; 46 = Y; etc.  Note:  48 and 49 are null characters, sometimes
          replaced with a "," or "."

 Putting It to Use
We will use the example cipher text:  "02901 14005 98605 97804"

Which breaks down into:  "D-E-C   I-P-H   E-R-T-H   E-A-R-G

Or:  "DECIPHER THE ARG"

Other Sources:
Practical Cryptography
Wikipedia
Quadibloc

The Tri-Digital Cipher:

Description
The tri-digital cipher is a variation on the straddling checkerboard, and is actually very similar.  However, the spaces are set in the last column by default and there is an extra step that involves using a ten-digit keyword or key phrase to set the order of the column-heading numbers.  Furthermore, the keyword or key phrase that is used within the table is actually composed of nine letters, as the last column is the only space left blank.  It is also important to note that this is harder than simply substituting letters for numbers like in the straddling checkerboard cipher, for all of the numbers except a couple have three letter possibilities.

Step-By-Step
Below is an example of a tri-digital setup, including a step-by-step description of how to compose the keyword alphabet used in decoding the cipher text:
  1. First and foremost, decide a ten-letter word or phrase that is going to be used to determine the order of the numbers that head the columns in the keyword alphabet.  I will use "CHRISJHORN" for this example.
  2. After deciding a keyword / key phrase, the next step is to assign the numbers 0-9 (with 0 being after 9--you can think of it as the number "10") to the letters in alphabetical order.  In the case that some letters are repeated, simply place the lower number in place of the first instance of that letter, and the next higher number in place of the second letter, so on and so forth.  In this example:
    C  H  R  I  S  J  H  O  R  N
    1  2  8  4  0  5  3  7  9  6

    Note that the first "H" gets 2, the second gets 3; the first "R" gets 8, the second gets 9
  3. Just like the straddling checkerboard, fill in the heading for the columns with the numbers 0-9 in the order you determined via the keyword / phrase:

1
2
8
4
0
5
3
7
9
6































     4.  The next step is to determine a 9-letter keyword or phrase.  This keyword or phrase can be
          composed of any letters, but repeat letters are excluded.  The first nine columns in the second
          row will be filled with these letters, leaving the last column (in this example, column "6")
          blank.  I will use the key phrase:  "I LOVE PIZZAS", which when I exclude repeat letters
          would break down into:  "I LOVE PZAS".  I then add this to the table under the numbers:

1
2
8
4
0
5
3
7
9
6
I
L
O
V
E
P
Z
A
S
-





















     5.  Then, much like the straddling checkerboard, fill in the rest of the letters of the alphabet, being
          sure to leave the last column blank.  There will also be another blank spot in the last row of the
          second-to-last column:

1
2
8
4
0
5
3
7
9
6
I
L
O
V
E
P
Z
A
S
-
B
C
D
F
G
H
J
K
M
-
N
Q
R
T
U
W
X
Y
-
-

     6.  Now that the keyword alphabet is composed, we can begin the tedious process of deciphering
          our cipher text.  It is important to understand that there are three possible letters for each of the
          numbers, except for the number in the last column which has no letters but is considered a
          space modifier, and the number in the second-to-last column which only has two possible
          letters.  The best way to do this is to start a table that lists the number, followed by the possible
          letters listed below it.  It is then easier to "eyeball" the different combinations and pick the
          combo that forms an actual word.

Putting It to Use:
We will use the example ciphertext:  "76257 22010 11062 15508"

First, break it down into a table that lists the possible letters for each number:

7
6
2
5
7
2
2
0
1
0
1
1
0
6
2
1
5
5
0
8
A
-
L
P
A
L
L
E
I
E
I
I
E
-
L
I
P
P
E
O
K
-
C
H
K
C
C
G
B
G
B
B
G
-
C
B
H
H
G
D
Y
-
Q
W
Y
Q
Q
U
N
U
N
N
U
-
Q
N
W
W
U
R

Then, pick only the letters that can form whole words--this is easier to do with the space modifier (6) separating the words:

7
6
2
5
7
2
2
0
1
0
1
1
0
6
2
1
5
5
0
8
A
-


A
L
L
E


I


-
I
P

E


-
C
H





G


G
-
C


H



-






N


N

-





R
 
Finally, simply copy down the resulting words and spaces:  "A CHALLENGING CIPHER"

Other Sources
American Cryptogram Association
ACA and You


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