Encrypt in C# and Decrypt in React

Hi Dave bell Please try the below sample

Encrypting Data in C#

using System;
using System.Security.Cryptography;
using System.Text;

public class AESEncryption
{
    public static string EncryptData(string dataToEncrypt, string key)
    {
        byte[] dataBytes = Encoding.UTF8.GetBytes(dataToEncrypt);
        byte[] keyBytes = Encoding.UTF8.GetBytes(key);

        using (Aes aesAlg = Aes.Create())
        {
            aesAlg.Key = keyBytes;
            aesAlg.GenerateIV(); // Generate a new IV (Initialization Vector) for each encryption

            ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);

            // Encrypt the data
            byte[] encryptedData;

            using (var ms = new System.IO.MemoryStream())
            {
                using (var cs = new CryptoStream(ms, encryptor, CryptoStreamMode.Write))
                {
                    cs.Write(dataBytes, 0, dataBytes.Length);
                }
                encryptedData = ms.ToArray();
            }

            // Combine IV and encrypted data into a single byte array
            byte[] combinedData = new byte[aesAlg.IV.Length + encryptedData.Length];
            Buffer.BlockCopy(aesAlg.IV, 0, combinedData, 0, aesAlg.IV.Length);
            Buffer.BlockCopy(encryptedData, 0, combinedData, aesAlg.IV.Length, encryptedData.Length);

            // Convert the combined data to Base64 string for easy transport
            return Convert.ToBase64String(combinedData);
        }
    }
}

Decrypting Data in React:

npm install crypto-js

Below is a React js code

import CryptoJS from 'crypto-js';

const DecryptData = (encryptedData, key) => {
  const combinedData = Buffer.from(encryptedData, 'base64');

  // Extract IV and encrypted data from the combined data
  const iv = combinedData.slice(0, 16);
  const encryptedBytes = combinedData.slice(16);

  const keyBytes = CryptoJS.enc.Utf8.parse(key);
  const ivBytes = CryptoJS.lib.WordArray.create(iv);

  const decryptedBytes = CryptoJS.AES.decrypt(
    { ciphertext: CryptoJS.lib.WordArray.create(encryptedBytes) },
    keyBytes,
    { iv: ivBytes }
  );

  // Convert the decrypted bytes to a UTF-8 string
  const decryptedData = decryptedBytes.toString(CryptoJS.enc.Utf8);
  return decryptedData;
};

According to your need adjust the code

you can use a symmetric encryption algorithm. Symmetric encryption uses a single secret key to both encrypt and decrypt data. This way, you can encrypt the email ID in C# before generating the URL and then decrypt it in your React app after reading the URL parameter.A gist of the process on how you can implement in C# and React  In C#, Use a symmetric encryption algorithm, such as AES (Advanced Encryption Standard), to encrypt the email ID along with the token. and then generate the URL with the encrypted email ID and the token. Use HttpUtility.UrlEncode to encode the complete URL (including the encrypted data) before sending it to the React app.

In the React App:

1. Use useParams() or any URL parsing library to retrieve the URL parameter containing the encrypted data.
2. Decode the URL parameter using decodeURIComponent() to get the encrypted data.
3. Implement the same symmetric encryption algorithm (AES) in the React app to decrypt the email ID using a shared secret key.
4. Once decrypted, you'll have the actual email ID, which you can use in your React app as needed.

Hope this solves your question.