BIFID CIPHERPREPARED BY:

HARNITA BINTI HARUN AMIN RASHIDNUR SARINA BINTI MOHD SADRI

NAJIHAH BINTI MOHAMAD ARBAIN

PISMP MATHS SEM 8

Introduction

cipher which combines the Polybius square with transposition, and uses fractionation to achieve diffusion

invented by Felix Delastelle was a Frenchman, invented several

ciphers including the bifid, trifid, and four-square ciphers

It has never been used by a military or government organisation, only ever by amateur cryptographers.

The Algorithm

Keys for the Bifid cipher usually consist of a 25 letter 'key square'. e.g.

1 2 3 4 51| a b c d e2| f g h i k3|l m n o p 4|q r s t u 5|v w x y z

the letters i and j are usually combined.

Eg:Plain text: H E L P

    Row: 2 1 3 3Column: 3 5 1 5

The Numbers: 21 33 35 15    Encoded: F  N  P  E

1 2 3 4 51| a b c d e2| f g h i k3|l m n o p 4|q r s t u 5|v w x y z

All non-letters are ignored and not encoded. The one skipped letter will be automatically translated if you type it in the box. Numbers, spaces, and punctuation will remain in place and will not be encoded.

To decrypt, the procedure is simply reversed. Longer messages are first broken up into blocks of fixed length, called the period. Each block is then encrypted separately. Odd periods are slightly more secure than even periods.

References

http://www.braingle.com/brainteasers/codes/polybius.php

http://www.purplehell.com/riddletools/bifid.htm

http://rumkin.com/tools/cipher/bifid.php