PortBlog.API/Shared/KBR.Shared/Extensions/ConfigurationExtensions.cs

using Microsoft.Extensions.Configuration;
using System.Security.Cryptography;
using System.Text;

namespace KBR.Shared.Extensions
{
    public static class ConfigurationExtensions
    {
        public static string EncryptConnectionString(this IConfiguration configuration, string plainConnectionString)
        {
            string keyBase64 = configuration.GetSection("ConnectionStrings:Key").Value;

            using (Aes aesAlgorithm = Aes.Create())
            {
                aesAlgorithm.Key = Convert.FromBase64String(keyBase64);
                aesAlgorithm.GenerateIV();
                aesAlgorithm.Mode = CipherMode.CBC;
                aesAlgorithm.Padding = PaddingMode.PKCS7;

                ICryptoTransform encryptor = aesAlgorithm.CreateEncryptor();

                byte[] encryptedData;
                using (MemoryStream ms = new MemoryStream())
                {
                    using (CryptoStream cs = new CryptoStream(ms, encryptor, CryptoStreamMode.Write))
                    {
                        byte[] plainBytes = Encoding.UTF8.GetBytes(plainConnectionString);
                        cs.Write(plainBytes, 0, plainBytes.Length);
                        cs.FlushFinalBlock();  // Explicitly apply padding
                    }
                    encryptedData = ms.ToArray();
                }

                string cipherBase64 = Convert.ToBase64String(encryptedData);
                string ivBase64 = Convert.ToBase64String(aesAlgorithm.IV);
                
                return $"{cipherBase64}:{ivBase64}";
            }
        }

        public static string DecryptConnectionString(this IConfiguration configuration, string encryptedConnectionString)
        {
            string keyBase64 = configuration.GetSection("ConnectionStrings:Key").Value;

            string vectorBase64 = encryptedConnectionString.Split(":")[1];
            string cipherText = encryptedConnectionString.Split(":")[0];

            using (Aes aesAlgorithm = Aes.Create())
            {
                aesAlgorithm.Key = Convert.FromBase64String(keyBase64);
                aesAlgorithm.IV = Convert.FromBase64String(vectorBase64);
                aesAlgorithm.Mode = CipherMode.CBC;
                aesAlgorithm.Padding = PaddingMode.PKCS7;

                ICryptoTransform decryptor = aesAlgorithm.CreateDecryptor();

                byte[] cipher = Convert.FromBase64String(cipherText);

                using (MemoryStream ms = new MemoryStream(cipher))
                {
                    using (CryptoStream cs = new CryptoStream(ms, decryptor, CryptoStreamMode.Read))
                    {
                        using (StreamReader sr = new StreamReader(cs, Encoding.UTF8))
                        {
                            return sr.ReadToEnd();
                        }
                    }
                }
            }
        }
    }
}