Tool to decrypt/encrypt AMSCO automatically. AMSCO is a transposition ciphering algorithm created by A.M.Scott which uses column transpositions.
AMSCO Cipher - dCode
Tag(s) : Transposition Cipher
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AMSCO Encryption consists in writing a text in a grid according to a cutting sequence then use a permutation key to switch columns.
Example: Encrypt the message DCODEAMSCO, with a cutting sequence 1,2 (alternation of 1 letter then 2 letters in the grid)
Select a permutation key (of length L), and write the message in lines, cut over L columns.
Example: If the key is KEY (equivalent to 2,1,3) of length 3, then write the message over 3 columns :
Read the grid in columns, in the order of the key (this reading serves as permutation).
Example: Column 2 (COM) then 1 (DEAO), and the 3 (DSC). The message is COMDEAODSC.
AMSCO decryption requires knowledge of the permutation key (of length L) and the cutting sequence (usually 1,2 or 2,1).
Example: Decrypt the message COMDEAODSC (of 10-characters length) with the key KEY (equivalent to the permutation 2,1,3) of length 3, and cutting sequence 1.2.
Create a table with L columns, in which the number of characters are noted in each cell (in respect to the cutting sequence and limited by the length of the message).
Example: 1,2 for 10 characters corresponds to (1+2+1+2+1+2+1+0+0 = 10) :
Write the message in the table in columns following the order of the columns indicated by the key.
Example: Write CO, then M in column 2, then D,EA,O in column 1, then D, DC in column 3. This leads to the grid:
The plain message is transcribed by reading the table in lines.
Example: Reading each lines gives the original plain text is DCODEAMSCO.
The text must alternate sizes of cuts which then should form diagonal sets:
Example: A grid of width 3, cut by (1,2):
Example: A grid of width 3, cut by (2,1):
Example: A grid of width 4, cut by (1,2):
Example: A grid of width 3, cut by (3,2,1):
It is possible to try to infer the key length by analyzing bigrams obtained after writing in columns.
AMSCO is a variant of the classical transposition cipher. It adds the cut sequence that can be more complex than the usual 1,2.
By A. M. Scott, in the 19th century