Play Fair Cipher

Play Fair Cipher comes under a Substitution cipher's category and this cipher was the first practical digraph substitution cipher. In play fair cipher unlike traditional cipher, we encrypt a pair/digraph of alphabets (digraphs) instead of a single alphabet.

Sample Test Case:

Key: "harry"
Plain Text: "My Name is Ravi"
Encrypted Text: "SF KBLF MO YRUK"
Decrypted Text: "MY NAME IS RAVI"

Note:*

Assume above test case throughout the discussion/process.
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