Encrypting Sensitive Data in ASP.NET Applications

To securely store and retrieve sensitive data like passwords or API keys in an ASP.NET app, you can use AES (Advanced Encryption Standard), a strong built-in encryption algorithm in .NET.

Here's a simple helper class I use for encrypting and decrypting strings:
 

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

public static class EncryptionHelper
{
    private static readonly string key = "MySecretKey12345"; // Must be 16, 24, or 32 characters

    public static string Encrypt(string plainText)
    {
        using (Aes aes = Aes.Create())
        {
            aes.Key = Encoding.UTF8.GetBytes(key);
            aes.GenerateIV(); // Create random IV
            ICryptoTransform encryptor = aes.CreateEncryptor();

            using MemoryStream ms = new();
            ms.Write(aes.IV, 0, aes.IV.Length); // Save IV at beginning
            using CryptoStream cs = new(ms, encryptor, CryptoStreamMode.Write);
            using (StreamWriter sw = new(cs))
            {
                sw.Write(plainText);
            }

            return Convert.ToBase64String(ms.ToArray()); // Return encrypted string
        }
    }

    public static string Decrypt(string encryptedText)
    {
        byte[] fullCipher = Convert.FromBase64String(encryptedText);

        using (Aes aes = Aes.Create())
        {
            byte[] iv = new byte[16];
            Array.Copy(fullCipher, iv, iv.Length);

            aes.Key = Encoding.UTF8.GetBytes(key);
            aes.IV = iv;

            ICryptoTransform decryptor = aes.CreateDecryptor();
            using MemoryStream ms = new(fullCipher, 16, fullCipher.Length - 16);
            using CryptoStream cs = new(ms, decryptor, CryptoStreamMode.Read);
            using StreamReader sr = new(cs);
            return sr.ReadToEnd(); // Return decrypted value
        }
    }
}

Example Usage:

// Encrypt your API key before saving
string encrypted = EncryptionHelper.Encrypt("my-real-api-key");
Console.WriteLine("Encrypted: " + encrypted);

// Decrypt it when needed
string decrypted = EncryptionHelper.Decrypt(encrypted);
Console.WriteLine("Decrypted: " + decrypted);

Important Notes:

• Don’t hardcode the key like this in real applications: store it in environment variables, Azure Key Vault, or user secrets.

• The above example uses a randomly generated IV (initialization vector) for better security, stored at the start of the encrypted text.

• AES is symmetric encryption: the same key is used to encrypt and decrypt.