Tools that apply Burrows-Wheeler algorithm. Burrows-Wheeler transform (BWT) is an algorithm maximizing repeated letters in a text, which is useful in data compression.

Burrows–Wheeler transform - dCode

Tag(s) : Compression,Algorithm

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Tools that apply Burrows-Wheeler algorithm. Burrows-Wheeler transform (BWT) is an algorithm maximizing repeated letters in a text, which is useful in data compression.

BWT ciphering rearranges letters in the messag.

The first step consists in listing all possible rotations the the message :

DECODE, EDECOD, DEDECO, ODEDEC, CODEDE, ECODED

and sort this list in alphabetical order

CODEDE, DECODE, DEDECO, ECODED, EDECOD, ODEDEC

The ciphered message is constituted of the last letters of each rotation : EEODDC and the key is the rank of the original message here 2 (DECODE is in position 2).

NB : dCode ignores all characters other than letters and digits, replacing them by a dot .

Decryption requires to know the key and the ciphered message.

EEODDC, clé 2

Do decrypt, one has to imagine an ampty table, and to repeat the folowing algorithm as many times as the number of letter in the message:

1) Write the message in the first column of the table (shifting the others columns) and 2) sort the lines of the table by alphabetic order

When achieved, the plain text is at the line number key of the table: DECODE

The ciphered message has a high number of repeated letters and a classic index of coincidence.

The key is not really important for intelligible text, because when decrypting, all lines of the table are in fact rotations of the original texte.

BWT can be used without key, but in this case, one has to know a unique character of the original text and its position, for instanct in computer one uses EOF for last one.

In 1994 by Michael Burrows and David Wheeler

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