Cifrar y descifrar contraseñas o cadenas de texto en C#

El Advanced Encryption Standard (AES), también conocido como Rijndael Encryption, fue desarrollado por dos criptógrafos belgas, Vincent Rijmen y Joan Daemen. AES ofrece una función para compartir o almacenar sus archivos de manera altamente segura. En este blog no hablamos de criptografía o AES, solo explica cómo cifrar y descifrar una cadena usando AES.

En el sistema de cifrado .Net Rijndael (Clase RijndaelManaged) es parte de la criptografía (System.Security.Cryptography). Esta clase nos permite cifrar y descifrar contraseñas o cualquier cadena de texto que quieran cifrar en c#.

public class SecurityManager
    {
        static readonly string password = "P455W0rd";
        public static string Encrypt(string plainText)
        {
            if (plainText == null)
            {
                return null;
            }
            // Get the bytes of the string
            var bytesToBeEncrypted = Encoding.UTF8.GetBytes(plainText);
            var passwordBytes = Encoding.UTF8.GetBytes(password);

            // Hash the password with SHA256
            passwordBytes = SHA512.Create().ComputeHash(passwordBytes);

            var bytesEncrypted = Encrypt(bytesToBeEncrypted, passwordBytes);

            return Convert.ToBase64String(bytesEncrypted);
        }

        /// <summary>
        /// Decrypt a string.
        /// </summary>
        /// <param name="encryptedText">String to be decrypted</param>
        /// <exception cref="FormatException"></exception>
        public static string Decrypt(string encryptedText)
        {
            if (encryptedText == null)
            {
                return null;
            }
            // Get the bytes of the string
            var bytesToBeDecrypted = Convert.FromBase64String(encryptedText);
            var passwordBytes = Encoding.UTF8.GetBytes(password);

            passwordBytes = SHA512.Create().ComputeHash(passwordBytes);

            var bytesDecrypted = Decrypt(bytesToBeDecrypted, passwordBytes);

            return Encoding.UTF8.GetString(bytesDecrypted);
        }

        private static byte[] Encrypt(byte[] bytesToBeEncrypted, byte[] passwordBytes)
        {
            byte[] encryptedBytes = null;
            var saltBytes = new byte[] { 1, 2, 3, 4, 5, 6, 7, 8 };

            using (MemoryStream ms = new MemoryStream())
            {
                using (RijndaelManaged AES = new RijndaelManaged())
                {
                    var key = new Rfc2898DeriveBytes(passwordBytes, saltBytes, 1000);

                    AES.KeySize = 256;
                    AES.BlockSize = 128;
                    AES.Key = key.GetBytes(AES.KeySize / 8);
                    AES.IV = key.GetBytes(AES.BlockSize / 8);

                    AES.Mode = CipherMode.CBC;

                    using (var cs = new CryptoStream(ms, AES.CreateEncryptor(), CryptoStreamMode.Write))
                    {
                        cs.Write(bytesToBeEncrypted, 0, bytesToBeEncrypted.Length);
                        cs.Close();
                    }

                    encryptedBytes = ms.ToArray();
                }
            }

            return encryptedBytes;
        }

        private static byte[] Decrypt(byte[] bytesToBeDecrypted, byte[] passwordBytes)
        {
            byte[] decryptedBytes = null;
            var saltBytes = new byte[] { 1, 2, 3, 4, 5, 6, 7, 8 };

            using (MemoryStream ms = new MemoryStream())
            {
                using (RijndaelManaged AES = new RijndaelManaged())
                {
                    var key = new Rfc2898DeriveBytes(passwordBytes, saltBytes, 1000);

                    AES.KeySize = 256;
                    AES.BlockSize = 128;
                    AES.Key = key.GetBytes(AES.KeySize / 8);
                    AES.IV = key.GetBytes(AES.BlockSize / 8);
                    AES.Mode = CipherMode.CBC;

                    using (var cs = new CryptoStream(ms, AES.CreateDecryptor(), CryptoStreamMode.Write))
                    {
                        cs.Write(bytesToBeDecrypted, 0, bytesToBeDecrypted.Length);
                        cs.Close();
                    }

                    decryptedBytes = ms.ToArray();
                }
            }

            return decryptedBytes;
        }
    }