Tool to decrypt/encrypt with modulo. Modulo calculations applied on numbers can make possible ciphering using the calculated values.

Modulo Cipher - dCode

Tag(s) : Homophonic Substitution Cipher

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A modulo cipher uses modular calculus on numbers in order to extract the remainder. The values obtained can then be used as a code/index for another cipher such as A1Z26 or the ASCII code.

Modulo Cipher Encryption uses modular arithmetics and a sequence of numbers, characters must be converted into numbers, e.g. `A=1`, `B=2`, … `Z=26`, but any numeric conversion (like the ASCII table) is fine.

__Example:__ To crypt `DCODE` with the modulo `26`, convert the text to numbers `4,3,15,4,5`.

For each number to encrypt, calculate a random number which value is equal to the number to crypt.

__Example:__ For $ 4 $, take $ 654 $, as $ 654 \equiv 4 \ mod 26 $

For $ 3 $, take $ 965 $, as $ 965 \equiv 3 \ mod 26 $.

The encrypted message is `654,965,561,732,941` (many other cipher message are possible)

Decryption requires to know the value of the Modulo and to know the series of number to decrypt.

__Example:__ The encrypted message is `654,965,561,732,941`with the modulo `26`.

For each number `N`, calculate the value of the remainder in the euclidean division of `N` by the modulo to get the plain number.

__Example:__ The plain text is `4,3,15,4,5`, that can be translate into `DCODE` with A1Z26 (A=1, B=2, etc.)

The ciphered message is constituted of somehow large random numbers.

The Affine cipher use modulo in the calculation $ C = a \times P + b \mod 26 $

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Cite as source (bibliography):

*Modulo Cipher* on dCode.fr [online website], retrieved on 2023-02-08,

modulo,cipher,remainder,division,calculator,modular,mod,modulus

https://www.dcode.fr/modulo-cipher

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