Encrypting Sensitive Data in ASP.NET Applications

Question

How to securely store and retrieve encrypted values (like passwords or API keys) using C#.

Divyansh Gupta · Answer

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.

Encrypting Sensitive Data in ASP.NET Applications

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