2 Playfair cipher Playfair is multipleletter encryption cipher

2 - Playfair cipher • Playfair: is multiple-letter encryption cipher based on the use of a 5 × 5 matrix of letters. Steps of Encryption 1) Repeating plaintext letters that are in the same pair are separated with a filler Letter. 2) Two plaintext letters that fall in the same row of the matrix are each replaced by the letter to the right, with the first element of the row circularly following the last. 3) Two plaintext letters that fall in the same column are each replaced by the letter beneath, with the top element of the column circularly following the last. 4) Otherwise, each plaintext letter in a pair is replaced by the letter that lies in its own row and the column occupied by the other plaintext letter.

Example/ encrypt the following message using playfair cipher? Key is "PROBLEMS"? Plaintext: “SHE WENT TO THE STORE”

Plaintext : SH EW EN TX TO TH ES TO RE Ciphertext: AG MV MK QY QB YT MA QB PM For decryption, if two ciphertext letters are on the same row or column, replace them with the two letters to the left or above, respectively. Otherwise, for each letter choose the letter on the same row and the other letter's column for decryption.

• Example/ Deccrypt the following message encrypt with playfair cipher? Key is "PROBLEMS"? Ciphertext: "AGMVMKQYQBYTMAQBPM" • Answer/ Ciphertext: AG MV MK QY QB YT MA QB PM Plaintext : SH EW EN TX TO TH ES TO RE plaintext message is “SHE WENT TO THE STORE”

• Characteristics ( security) of playfair • Security much improved over monoalphabetic because it have 26*26 letters. • Widely used for many years. • It can broken.

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