Key Concepts Related to Decryption

1. Ciphertext

• Encrypted data that's unreadable without decryption.

2. Decryption Key

• Secret/private key used to decode encrypted data.

3. Algorithm

• Same algorithm must be used for both encryption and decryption.

4. Initialization Vector (IV)

• Used to ensure randomness and uniqueness. Must also be known or transferred securely for decryption.

5. Key Management

• Crucial for both encryption and decryption; loss of a key can result in data loss.

Symmetric Decryption

• Same key is used to encrypt and decrypt.
• Fast and efficient, but key sharing must be secure.
• Common in:
  • Encrypted database fields
  • File decryption
  • Application configuration

Asymmetric Decryption

• Data encrypted with a public key is decrypted with a private key.
• More secure for communication and identity verification.
• Common in:
  • Secure emails (PGP)
  • HTTPS/TLS (SSL certificates)
  • Digital signature validation

Not Decryptable: Hashing

• Hashing is a one-way function and cannot be decrypted.
• Instead, the original value is hashed again and compared with the stored hash.

C# Console Application that demonstrates:

• AES Symmetric Encryption & Decryption
• RSA Asymmetric Encryption & Decryption
• SHA-256 Hashing (One-Way)

// EncryptionDecryptionConsoleApp.cs
using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

class EncryptionDecryptionConsoleApp
{
    static void Main()
    {
        Console.WriteLine("--- Encryption & Decryption Console App ---\n");

        string originalText = "Hello World!! \n" +
            " Welcome to C# Corner \n " +
            "Encryption & Decryption Article";
        string aesKey = "1234567890123456"; // 16 characters = 128-bit key
        string aesIV = "6543210987654321";  // 16 characters = 128-bit IV

        // Symmetric AES Encryption
        string encryptedAES = EncryptAES(originalText, aesKey, aesIV);
        Console.WriteLine($"\n AES Encrypted:\n {encryptedAES}");

        string decryptedAES = DecryptAES(encryptedAES, aesKey, aesIV);
        Console.WriteLine($"\n AES Decrypted:\n {decryptedAES}\n");

        // Asymmetric RSA Encryption/Decryption
        using var rsa = RSA.Create(2048);
        byte[] originalBytes = Encoding.UTF8.GetBytes(originalText);
        byte[] encryptedRSA = rsa.Encrypt(originalBytes, RSAEncryptionPadding.OaepSHA256);
        string encryptedRSAString = Convert.ToBase64String(encryptedRSA);
        Console.WriteLine($"\n RSA Encrypted:\n {encryptedRSAString}");

        byte[] decryptedRSA = rsa.Decrypt(encryptedRSA, RSAEncryptionPadding.OaepSHA256);
        Console.WriteLine($"\n RSA Decrypted:\n {Encoding.UTF8.GetString(decryptedRSA)}\n");

        // Hashing Example (SHA256)
        string hashed = HashSHA256(originalText);
        Console.WriteLine($"SHA-256 Hashed (one-way): {hashed}");

        Console.WriteLine("\nPress any key to exit...");
        Console.ReadKey();
    }

    static string EncryptAES(string plainText, string key, string iv)
    {
        using Aes aes = Aes.Create();
        aes.Key = Encoding.UTF8.GetBytes(key);
        aes.IV = Encoding.UTF8.GetBytes(iv);

        using var encryptor = aes.CreateEncryptor(aes.Key, aes.IV);
        using var ms = new MemoryStream();
        using (var cs = new CryptoStream(ms, encryptor, CryptoStreamMode.Write))
        using (var sw = new StreamWriter(cs))
            sw.Write(plainText);

        return Convert.ToBase64String(ms.ToArray());
    }

    static string DecryptAES(string cipherText, string key, string iv)
    {
        byte[] cipherBytes = Convert.FromBase64String(cipherText);
        using Aes aes = Aes.Create();
        aes.Key = Encoding.UTF8.GetBytes(key);
        aes.IV = Encoding.UTF8.GetBytes(iv);

        using var decryptor = aes.CreateDecryptor(aes.Key, aes.IV);
        using var ms = new MemoryStream(cipherBytes);
        using var cs = new CryptoStream(ms, decryptor, CryptoStreamMode.Read);
        using var sr = new StreamReader(cs);
        return sr.ReadToEnd();
    }

    static string HashSHA256(string text)
    {
        using SHA256 sha256 = SHA256.Create();
        byte[] bytes = Encoding.UTF8.GetBytes(text);
        byte[] hash = sha256.ComputeHash(bytes);
        return BitConverter.ToString(hash).Replace("-", "").ToLower();
    }
}

Output
------------------------------
--- Encryption & Decryption Console App ---


 AES Encrypted:
 hVF5CJzPIU6cIVktU7nmt9+Sp6TI9OJbOV4UxuAlozRAgEzCEFh9FYNQBkDxxhsvGm3zEQev4oSc0VLFnIo8k716ncg1xDhdMwgpF50FZog=

 AES Decrypted:
 Hello World!!
 Welcome to C# Corner
 Encryption & Decryption Article


 RSA Encrypted:
 H27Ba8N1lNw6c8P80PNczMDoLUP56q3rMo9kbnL+9Je29Lx0PFkMjckQk5dnOyrkqgXL6GiKz7Cmzz30xevQLF6lVER9/UkblKZSkrPs8k33++4csLEo760yCXiqZfNIrfYNzRNx1crX8PqJYtOjEGi6dL/Dxuahtm4gjZ5EGhuZ/G8VJaTDir/Ixxj9Z54Ki7s0U8Oc/jqCXWr03klSlMhcXZjLt5B9l7Gn+9IgtUXcGCZNi/VuiUPbbB4ql5ANqqgA5lLla9SlLx1aa9p4b/7oag4WZZJZC3HhVeVzRcx25a+UMCsNzPOjzHTRIFbxDi8ukuUmVx81/fZlOfNmqg==

 RSA Decrypted:
 Hello World!!
 Welcome to C# Corner
 Encryption & Decryption Article

SHA-256 Hashed (one-way): 2b9a99da60ee437e2f663f0085fb1de5a13c43237a10af875e4bb35231552d50

In today’s digital world, encryption and decryption are no longer optional — they are essential building blocks of secure software and data protection. Whether you're safeguarding user credentials, securing communication between services, or ensuring compliance with data protection laws, understanding how to implement and apply encryption effectively is a must for every developer.

Security isn't just a feature — it's a responsibility. By integrating proper encryption and decryption techniques in your applications, you not only protect sensitive data but also build trust, achieve regulatory compliance, and ensure system reliability.

Thank you for taking the time to read this post. I hope it has provided you better understanding of encryption and decryption and empowers you to apply these techniques effectively in real-world projects.

Keep learning, keep practicing, and keep building secure software.