Tool to decrypt monoalphabetical substitution and find each letter of a substituted message with a deranged alphabet (monoalphabetic cipher).

Alphabetical Substitution - dCode

Tag(s) : Cryptography, Substitution Cipher

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Tool to decrypt monoalphabetical substitution and find each letter of a substituted message with a deranged alphabet (monoalphabetic cipher).

The monoalphabetical substitution consists in using a mixed alphabet (with the letters in an unusual order) and replace the letters of the alphabet normal by it.

Example: NBAJYFOWLZMPXIKUVCDEGRQSTH is a totally random alphabet with the 26 letters of the Latin alphabet.

We can write the alphabet over the classic alphabet to better understand:

Plain alphabet | ABCDEFGHIJKLMNOPQRSTUVWXYZ |
---|---|

Substution alphabet | NBAJYFOWLZMPXIKUVCDEGRQSTH |

The substitution involves replacing the plaintext of all the letters of the first row with the letters associated with the second row.

Example: All A become N, all the B remain B, all the C become A, etc.

Example: With this substitution DCODE is encrypted as JAKJY.

Any deranged alphabet can be used to create a single alphabetical substitution (the same letter can be used only once in the alphabet).

Decryption requires knowing the alphabet mixed used and the inverse substitution encryption.

Substitution Alphabet | NBAJYFOWLZMPXIKUVCDEGRQSTH |
---|---|

Plain Alphabet | ABCDEFGHIJKLMNOPQRSTUVWXYZ |

The substitution involves replacing in the ciphertext all the letters of the first row with the letters associated with the second row.

Example: Consider the encrypted message JAKJY, then the plain message is DCODE.

The ciphered message has an index of coincidence identical to the language of the plain text.

The interactive tool provided by dCode allows a semi-automatic decryption of messages ciphered by substitution.

The main technique is to analyze the frequencies of letters and find the most likely bigrams.

Example: The most common alphabets used for substitutions are: AZERTYUIOPQSDFGHJKLMWXCVBN

NBVCXWMLKJHGFDSQPOIUYTREZA

QWERTYUIOPASDFGHJKLZXCVBNM

MNBVCXZLKJHGFDSAPOIUYTREWQ

AQWZSXEDCRFVTGBYHNUJIKOLPM

ZYXWVUTSRQPONMLKJIHGFEDCBA

'AEIOUYBCDFGHJKLMNPQRSTVWXZ

First some substutition use specific alphabets, as Atbash that takes the alphabet backwards ZYXWVUTSRQPONMLKJIHGFEDCBA or the Caesar cipher which uses a shifted alphabet DEFGHIJKLMNOPQRSTUVWXYZABC that is shifted by 3. Then there are substitutions that use several alphabets, such as alphabet that changes depending on an algorithm defined by encryption (e.g. Vigenere uses 26 alphabets).

dCode retains ownership of the source code of the script Alphabetical Substitution. Except explicit open source licence (indicated Creative Commons / free), any algorithm, applet, snippet, software (converter, solver, encryption / decryption, encoding / decoding, ciphering / deciphering, translator), or any function (convert, solve, decrypt, encrypt, decipher, cipher, decode, code, translate) written in any informatic langauge (PHP, Java, C#, Python, Javascript, etc.) which dCode owns rights can be transferred after sales quote. So if you need to download the Alphabetical Substitution script for offline use, for you, your company or association, see you on contact page !

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Source : http://www.dcode.fr/monoalphabetic-substitution

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