Amsco

History

The Amsco cipher is an incomplete columnar transposition cipher invented by American Cryptogram Association (ACA) member A M Scott, whose members name was AMSCO, and was mentioned in Cryptanalysis: A Study of Ciphers and Their Solution, first published as Elementary Cryptanalysis, 1939 by Helen Fouché Gaines (1888-1940). It differs from the regular incomplete columnar transposition cipher in that plain text is alternatively written in the block in pairs and single letters.

Description

To create the cipher a key is selected, which determines the width of a block, and then plaintext is written into the block horizontally below the key. Both the rows and columns always alternate between digraphs and single letters then each column is read off vertically to form the cipher. The order in which the columns are read is determined by the numeric order of the keyword.

Example

Key: 31452

Plaintext: A person who smiles in the face of adversity probably has a scapegoat.

3 1 4 5 2

AP E RS O NW

H OS M IL E

SI N TH E FA

C EO F AD V

ER S IT Y PR

O BA B LY H

AS A SC A PE

G OA T

Ciphertext: EOSNE OSBAA OANWE FAVPR HPEAP HSICE ROASG RSMTH FITBS CTOIL EADYL YA

Solving

Solving method: Brute force search.

After selecting the Amsco cipher, the cipher period can be selected from the Setup drop down menu. The default setting of 0 will result in all periods in the keyword range set in the Options window being tested.