public static string EncryptString(string text, string keyString)
{
    var key = Encoding.UTF8.GetBytes(keyString);

    using (var aesAlg = Aes.Create())
    {
        using (var encryptor = aesAlg.CreateEncryptor(key, aesAlg.IV))
        {
            using (var msEncrypt = new MemoryStream())
            {
                using (var csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
                using (var swEncrypt = new StreamWriter(csEncrypt))
                {
                    swEncrypt.Write(text);
                }

                var iv = aesAlg.IV;

                var decryptedContent = msEncrypt.ToArray();

                var result = new byte[iv.Length + decryptedContent.Length];

                Buffer.BlockCopy(iv, 0, result, 0, iv.Length);
                Buffer.BlockCopy(decryptedContent, 0, result, iv.Length, decryptedContent.Length);

                return Convert.ToBase64String(result);
            }
        }
    }
}