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** is a (incomplete) columnar transposition cipher performing a permutation of an alternation of bigrams and unigrams of the plaintext.

**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, both in rows and in columns)

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:

\ | 1 | 2 | 3 |
---|---|---|---|

D | CO | D | |

EA | M | SC | |

O |

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) :

\ | 1 | 2 | 3 |
---|---|---|---|

1 | 2 | 1 | |

2 | 1 | 2 | |

1 | 0 | 0 |

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:

\ | 1 | 2 | 3 |
---|---|---|---|

D | CO | D | |

EA | M | SC | |

O |

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 (even if the key size is even) which then should form diagonal sets:

__Example:__ A grid of width 3, cut by (1,2):

\ | 1 | 2 | 3 |
---|---|---|---|

1 | 2 | 1 | |

2 | 1 | 2 | |

1 | 2 | 1 |

__Example:__ A grid of width 3, cut by (2,1):

\ | 1 | 2 | 3 |
---|---|---|---|

2 | 1 | 2 | |

1 | 2 | 1 | |

2 | 1 | 2 |

__Example:__ A grid of width 4, cut by (1,2):

\ | 1 | 2 | 3 | 4 |
---|---|---|---|---|

1 | 2 | 1 | 2 | |

2 | 1 | 2 | 1 | |

1 | 2 | 1 | 2 |

__Example:__ A grid of width 3, cut by (3,2,1):

\ | 1 | 2 | 3 |
---|---|---|---|

3 | 2 | 1 | |

2 | 1 | 3 | |

1 | 3 | 2 |

No need to fill the grid with null letters if a cell is empty or incomplete.

The ciphered message is subjected to a single transposition, so it has an index of coincidence similar to the one of the plain text.

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`.

**AMSCO** dates from the 19th and bear the initials of its author A. M. Scott

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NB: for encrypted messages, test our automatic cipher identifier!

- AMSCO Decoder
- AMSCO Encoder
- What is AMSCO cipher? (Definition)
- How to encrypt using AMSCO cipher?
- How to decrypt AMSCO cipher?
- How to correctly split the text into the grid?
- How to recognize AMSCO ciphertext?
- How to decipher AMSCO without a key?
- What are the variants of the AMSCO cipher?
- When was AMSCO invented?

amsco,scott,column,transposition,grid

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