AMSCO Cipher

The AMSCO Cipher is a transposition cipher that rearranges the letters of a message using a keyword and an alternating cell pattern. Unlike simple columnar transposition, AMSCO alternates between placing one and two characters in each cell, following a continuous pattern (1-2 or 2-1) across the entire message.

The cipher operates in three phases: first, a structure of cell sizes is generated based on the key length and pattern. Next, the plaintext is filled into this structure row by row. Finally, the columns are read in the order determined by alphabetically sorting the key.

AMSCO Cipher: Encoding

Using the keyword ZEBRA, pattern 1-2, and input HELLO WORLD (with spaces preserved):

Plaintext: HELLO WORLD
Key:       Z E B R A
Pattern:   1-2

Step 1: Build structure (cell sizes per column)

Z: [1, 2]
E: [2, 1]
B: [1, 2]
R: [2, 1]
A: [1]

Step 2: Fill row by row using the structure

Z     E     B     R     A
----------------------------
H     EL    L     O     ˽
WO    R     LD

Step 3: Determine key order (alphabetical)

A B E R Z

Step 4: Read columns in that order

A: ˽
B: L LD
E: EL R
R: O
Z: H WO

Ciphertext: wldello hor

AMSCO Cipher: Decoding

To decode, rebuild the same structure, then split the ciphertext into column segments based on that structure, and finally read row by row:

Ciphertext: wldello hor
Key:        ZEBRA
Pattern:    1-2

Step 1: Rebuild structure

Z: [1, 2]
E: [2, 1]
B: [1, 2]
R: [2, 1]
A: [1]

Step 2: Determine column lengths

Z: 3 letters
E: 3 letters
B: 3 letters
R: 3 letters
A: 1 letter

Step 3: Fill columns in key order (A B E R Z)

A: ˽
B: L LD
E: EL R
R: O
Z: H WO

Step 4: Read row by row

Row 1: H EL L O ˽
Row 2: WO R LD

Plaintext: HELLO WORLD

AMSCO Cipher: Notes

The alternating pattern (1-2 or 2-1) is applied continuously across the entire message. The structure is defined as cell sizes per column before any text is placed. The plaintext is filled row by row using that structure. Column order is determined by sorting the key alphabetically, preserving original order for duplicate letters. Spaces are treated as normal characters when included, affecting both structure and output. The irregular grouping of characters makes AMSCO more complex than standard columnar transposition.