Homophonic Substitution Cipher

Homophonic Substitution Cipher

1. HOMOPHONIC SUBSTITUTION
CIPHER
Prof. Neeraj Bhargava
Mrs. Shubha Chaturvedi
Department of Computer Science, School of Engineering & System Sciences
MDS University Ajmer, Rajasthan

2. •TheHomophonicSubstitutioncipherisasubstitutioncipherin
whichsingleplaintextletterscanbereplacedbyanyofseveral
differentciphertextletters.Theyaregenerallymuchmore
difficulttobreakthanstandardsubstitutionciphers.
Thenumberofcharacterseachletterisreplacedbyispartof
thekey,e.g.theletter'E'mightbereplacedbyanyof5
differentsymbols,whiletheletter'Q'mayonlybesubstituted
by1symbol.
HOMOPHONIC SUBSTITUTION
CIPHER

3. • ThePolybiussquare,alsoknownasthePolybiuscheckerboard.
• Itis5*5gridthatallowstoencryptlettersintonumbers.
• ItisadeviceinventedbytheancientGreeksCleoxenusand
Democleitus,andmadefamousbythehistorianandscholarPolybius.
• Eachletteristhenrepresentedbyitscoordinatesinthegrid.
• The26lettersoftheLatin/Englishalphabetdonotfitina5×5
square,twolettersmustbecombined(usuallyIandJasabove,
thoughCandKisanalternative).Alternatively,a6×6gridmaybe
usedtoallownumeralsorspecialcharacterstobeincludedaswellas
letters.
POLYBIUS/POLYBIUS CHECKBOARD

4. EXAMPLE :
Find out the polybius square cipher for the plain text “university”?
STEP-1
First we will create a matrix 5*5 ,in order to fit 26 letters of the English
Alphabet into the 25 spots letter I and J usually combined.
1 2 3 4 5
1
2
3
4
5
A B C D E
F G H I/J K
L M N O P
Q R S T U
V W X Y Z

5. STEP-2
Assign the number to letter in the plain text from the
about to get cipher text.
PLAINTEXT :
U N I V E R S I T Y
CIPHER TEXT :
45 33 24 51 15 42 43 24 44 54

6. Q. Find out the polybius square cipher for the
plain text “RAJASTHAN”?
Assignment