Cryptography - Vigenère Cipher

practice C++ and creating Encryption Algorithms

initially created on repl.it

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encrypt: Ci = (Pi + Kj) mod 26

• implicit typecast conversion to ASCII code
• add up values
• mod 26 converting sum to 0-25

decrypt: Pi = (Ci – Kj) mod 26

• implicit typecast conversion to ASCII code
• subtract values and add 26 (for neg nums)
• mod 26 converting to 0-25
• int decipherIndex = (cipherText[i] - key[i] + 26) % 26;

C = cipher text

P = plain text

K = key char - alpha key to derive cipher text offset

i = the ith character in the plain text, corresponding with cipher text index

j = jth character of the key

mod 26 returns an index within alphabetic range, 0-25

ASCII

Utilizing ASCII table's mapping of character to decimal code to convert alphabet to integer, and vice versa.

Issues

Present issues with code here.