PYTHON : THE SUBSTITUTION CIPHER - ENCRYPTING & DECRYPTING

    My GitHub code : https://github.com/devmecha/THE_SUBSTITUTION_CIPHER-

In cryptography, a substitution cipher is a method of encrypting by which units of plaintext are replaced with ciphertext, according to a fixed system; the "units" may be single letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth. The receiver deciphers the text by performing the inverse substitution.
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