Encryption-Decryption Like a Student Thought

I am describe an algorithm with practical steps proves with C# code or you can perform it in any language it's your choice. Graphic layout of tool works on this algorithm is depends on your thoughts.

Description of Algorithm

A simple algorithm works with & play with an ASCII value of characters.

Algorithm works within 6 different steps.

Step 1: Convert input string characters in respected ASCII codes & store it in array like below mentioned example of C# code.

ArrayList asciiArr = new ArrayList();

for (int i = 0; i < inputString.Length; i++) {
    asciiArr.Add((int) Convert.ToChar(inputString[i]));
}
or(i = 0; i < inputString.length; i++) {
    asciiArr[i] = inputString[i].charCodeAt(0);
}

Step 2: Fill A to Z array in capital or small letters.

ArrayList atozArr = new ArrayList();

for (int i = 0, j = 65; i < 26; i++, j++)
{
   atozArr.Add((char) j);
}

Step 3: Choose randomly single character index from A to Z and differentiate it's position in one variable & it's respected ASCII value in second variable.

Note: Here i'm referencing an function return a random value from minimum - maximum range.

int positionAscii = Convert.ToInt32(atozArr[(new Random()).Next(26)]);

Step 4: Addition of every input String each element to positionAscii.

ArrayList outputArr = new ArrayList();

for (int i = 0; i < inputString.Length; i++) {
    outputArr.Add(Convert.ToInt32(asciiArr[i]) + positionAscii);
}

int[] k = (int[]) outputArr.ToArray(System.Type.GetType("System.Int32"));

Console.Write("\nCipher Text: \n\n");

foreach(int i in k) {
    cipherText = cipherText + (char) i;
}

Step 5: Attachment of key to encrypted string or not it's your choice & it's your modification scenario, here i am attaching a key with an encrypted string:

if (inputString.Length.Equals(cipherText.Length))
{
   cipherText = cipherText + (char)positionAscii;
}

Step 6: Finally your encryption is ready to send.

return cipherText;

For decryption process reverse steps apply.

Note: Every time cypher text will change due to selection of randomposition from A to Z.

Below mention code is print your output cipher text to text file.

string output = "";
// Write each directory name to a file.
using (StreamWriter sw = new StreamWriter("output.txt"))
{
   output = encryption(input);
   sw.WriteLine(output);
}

C# Code for Practice

function encryption() {
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Collections;
    using System.IO;

    namespace Codeblank {
        class Program {
            private static string encryption(string inputString) {
                string cipherText = "";

                //Step : 1
                //Convert input string characters in respected ascii codes & store it in array like below mentioned example of C# code.

                ArrayList asciiArr = new ArrayList();

                for (int i = 0; i < inputString.Length; i++) {
                    asciiArr.Add((int) Convert.ToChar(inputString[i]));
                }

                //Step : 2
                //Fill A to Z array in capital or small letters

                ArrayList atozArr = new ArrayList();

                for (int i = 0, j = 65; i < 26; i++, j++) {
                    atozArr.Add((char) j);
                }

                //Step : 3
                // Choose randomly single character index from A to Z and differentiate it's position in one variable & it's respected ascii value in second variable
                //Note: Here i'm referencing an function return a random value from minimum - maximum range.

                int positionAscii = Convert.ToInt32(atozArr[(new Random()).Next(26)]);

                //Step : 4
                //Addition of every input String each element to positionAscii

                ArrayList outputArr = new ArrayList();

                for (int i = 0; i < inputString.Length; i++) {
                    outputArr.Add(Convert.ToInt32(asciiArr[i]) + positionAscii);
                }

                int[] k = (int[]) outputArr.ToArray(System.Type.GetType("System.Int32"));

                Console.Write("\nCipher Text: \n\n");

                foreach(int i in k) {
                    cipherText = cipherText + (char) i;
                }

                //Step : 5
                //Attachment of key to encrypted string or not it's your choice & it's your modification scenario, here i'm attaching a key with an encrypted string

                if (inputString.Length.Equals(cipherText.Length)) {
                    cipherText = cipherText + (char) positionAscii;
                }

                //Step : 6
                //Finally your encryption is ready to send
                return cipherText;
            }

            private static string decryption(string cipherText) {
                //Step : 1
                //Take decryption key from cipherText

                int positionAscii = Convert.ToInt32(cipherText[cipherText.Length - 1]);

                //Step : 2
                //Substract value of key from each characters of cipherText

                string plainText = "";

                foreach(int i in cipherText) {
                    plainText = plainText + (char)(Convert.ToInt32(i) - positionAscii);
                }

                return plainText;
            }

            static void Main(string[] args) {
                Console.Write("Plain Text: \n\n");
                string input = Console.ReadLine();
                string output = "";
                // Write each directory name to a file.
                using(StreamWriter sw = new StreamWriter("output.txt")) {
                    output = encryption(input);
                    sw.WriteLine(output);
                }
                Console.Write(output);
                Console.WriteLine("\n\nAfter Decryption Plain Text: \n\n" + decryption(output));
                Console.ReadKey();

            }
        }
    }

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