Question

Construct a Playfair matrix with the key RHYME

Use the playfair matrix you just constructed and decrypt the following message: "PEYFQUGVHSMFPURHPERESUTG". Make sure you use your knowledge of the plaintext language and decide whether to use I or J in the decrypted message. Remove all filler letters, separate out the words when writing the final answer.

Note: Place I and J in the same cell and assume filler letter is X.

Answer 1

Key : RHYME

Playfair matrix

R	H	Y	M	E
A	B	C	D	F
G	I/J	K	L	N
O	P	Q	S	T
U	V	W	X	Z

Encrypted Message : "PEYFQUGVHSMFPURHPERESUTG"

Grouping the encrypted message as a pair of two letters each , the following will be the result :

PE YF QU GV HS MF PU RH PE RE SU TG

To decrypt the cipher we need to consider each pair mentioned above in reference with the playfair matrix.

• Pair 1

PE - to decrypt this pair , first consider P’s row and E’s column which will encounter the cell that contains “T”.

Next consider the opposite i.e.; E’s row an P’s column which will encounter the cell that contains “H”.

   Therefore PE =TH

  

R	H	Y	M	E
A	B	C	D	F
G	I/J	K	L	N
O	P	Q	S	T
U	V	W	X	Z

R	H	Y	M	E
A	B	C	D	F
G	I/J	K	L	N
O	P	Q	S	T
U	V	W	X	Z

• Pair 2

YF - to decrypt this pair , first consider Y’s row and F’s column which will encounter the cell that contains “E”. Next consider the opposite i.e.; F’s row and Y’s column which will encounter the cell that contains “C”.

Therefore PF =EC

• Pair 3

QU -

Q’s row and U’s column=“O”.

U’s row and Q’s column =“W”.

   Therefore QU =OW

• Pair 4

GV -

G’s row and V’s column=“I” (Here you can take either J or I, but after complete decryption the message should make some sense)

V’s row and G’s column =“U”.

Therefore GV =IU    

Likewise we need to decrypt each and every pair. In doing so the following pairs are decrypted as :

• Pair 5 = “H S” = “MP”
• Pair 6 = “M F” = “ED”
• Pair 7 = “P U” = “OV”
• Pair 8

RH =

Here,R and H come in the same row. Now in this case , take the letter to the left of each one (going back to the rightmost if at the leftmost position).   

The letter to the left of R is “E” and to the left of H is “R”   

Therefore “RH” is decrypted as “ER”

R	H	Y	M	E
A	B	C	D	F
G	I/J	K	L	N
O	P	Q	S	T
U	V	W	X	Z

R	H	Y	M	E
A	B	C	D	F
G	I/J	K	L	N
O	P	Q	S	T
U	V	W	X	Z

• Pair 9 = “P E” = “T H”
• Pair 10

RE comes in the same row as well . So , take the letter to the left of each one (going back to the rightmost if at the leftmost position).

The letter to the left of R is “E” and to the left of E is “M”

Therefore “RE” is decrypted as “EM”

• Pair 11 = “S U” = “O X”
• Pair 12 = “T G” = “O N”

The decrypted letters are : " THECOWIUMPEDOVERTHEMOXON "

Arranging the letters into meaningful words : " THE COW IUMPED OVER THE MOXON"

Now the above decrypted message seems similar to " The cow jumped over the moon"

So instead of taking "I" in the decrypted message , we need to take " J "

And It is given in the question that , all filler letter need to be removed which is " X " here.

Therefore our decrypted message is :

" THE COW JUMPED OVER THE MOON "

NOTE : In the playfair matrices shown, the blue coloured letter is used to indicate the selected row and column, while the red coloured elements are the corresponding decrypted letters.