c# How to Get URL of CRL (Revocation list) from x509 certificate

using section. 

using System;
using System.ComponentModel;
using System.Linq;
using System.Net;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;
using System.Runtime.InteropServices;
using System.Text.RegularExpressions;

Main method is GetBaseCrlURL()

        private const string CERT_CRL_EXTENSION = "2.5.29.31";
        private const string CRL_CRL_EXTENSION = "2.5.29.46";
 
        public static string GetBaseCrlUrl(X509Certificate2 cert)
        {
            try
            {
                return (from X509Extension extension in cert.Extensions
                        where extension.Oid.Value.Equals(CERT_CRL_EXTENSION)
                        select GetCrlUrlFromExtension(extension)).Single();
            }
            catch
            {
                return null;
            }
        }
 
        private static string GetDeltaCrlUrl(WinCrypt32.CRL_INFO stCrlInfo)
        {
            IntPtr rgExtension = stCrlInfo.rgExtension;
            X509Extension deltaCrlExtension = null;
 
            for (int i = 0; i < stCrlInfo.cExtension; i++)
            {
                WinCrypt32.CERT_EXTENSION stCrlExt = (WinCrypt32.CERT_EXTENSION)Marshal.PtrToStructure(rgExtension, typeof(WinCrypt32.CERT_EXTENSION));
 
                if (stCrlExt.Value.pbData != IntPtr.Zero && stCrlExt.pszObjId == CRL_CRL_EXTENSION)
                {
                    byte[] rawData = new byte[stCrlExt.Value.cbData];
                    Marshal.Copy(stCrlExt.Value.pbData, rawData, 0, rawData.Length);
                    deltaCrlExtension = new X509Extension(stCrlExt.pszObjId, rawData, stCrlExt.fCritical);
                    break;
                }
 
                rgExtension = (IntPtr)((Int32)rgExtension + Marshal.SizeOf(typeof(WinCrypt32.CERT_EXTENSION)));
            }
            if (deltaCrlExtension == null)
            {
                return null;
            }
            return GetCrlUrlFromExtension(deltaCrlExtension);
        }
 
        private static string GetCrlUrlFromExtension(X509Extension extension)
        {
            try
            {
                Regex rx = new Regex("http://.*crl");
                string raw = new AsnEncodedData(extension.Oid, extension.RawData).Format(false);
                return rx.Match(raw).Value;
            }
            catch
            {
                return null;
            }
        }

It's class helper WinCrypt32

public static class WinCrypt32
    {
        #region APIs
 
        [DllImport("CRYPT32.DLL", EntryPoint = "CryptQueryObject", CharSet = CharSet.Auto, SetLastError = true)]
        public static extern Boolean CryptQueryObject(
            Int32 dwObjectType,
            IntPtr pvObject,
            Int32 dwExpectedContentTypeFlags,
            Int32 dwExpectedFormatTypeFlags,
            Int32 dwFlags,
            IntPtr pdwMsgAndCertEncodingType,
            IntPtr pdwContentType,
            IntPtr pdwFormatType,
            ref IntPtr phCertStore,
            IntPtr phMsg,
            ref IntPtr ppvContext
            );
 
        [DllImport("CRYPT32.DLL", EntryPoint = "CertFreeCRLContext", SetLastError = true)]
        public static extern Boolean CertFreeCRLContext(
            IntPtr pCrlContext
        );
 
        [DllImport("CRYPT32.DLL", EntryPoint = "CertNameToStr", CharSet = CharSet.Auto, SetLastError = true)]
        public static extern Int32 CertNameToStr(
            Int32 dwCertEncodingType,
            ref CRYPTOAPI_BLOB pName,
            Int32 dwStrType,
            StringBuilder psz,
            Int32 csz
        );
 
        [DllImport("CRYPT32.DLL", EntryPoint = "CertFindExtension", CharSet = CharSet.Auto, SetLastError = true)]
        public static extern IntPtr CertFindExtension(
            [MarshalAs(UnmanagedType.LPStr)]String pszObjId,
            Int32 cExtensions,
            IntPtr rgExtensions
        );
 
        [DllImport("CRYPT32.DLL", EntryPoint = "CryptFormatObject", CharSet = CharSet.Auto, SetLastError = true)]
        public static extern Boolean CryptFormatObject(
            Int32 dwCertEncodingType,
            Int32 dwFormatType,
            Int32 dwFormatStrType,
            IntPtr pFormatStruct,
            [MarshalAs(UnmanagedType.LPStr)]String lpszStructType,
            IntPtr pbEncoded,
            Int32 cbEncoded,
            StringBuilder pbFormat,
            ref Int32 pcbFormat
        );
 
        #endregion APIs
 
        #region Structs
        [StructLayout(LayoutKind.Sequential)]
        public struct CRYPT_OBJID_BLOB
        {
            public uint cbData;
            [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 0)]
            public byte[] pbData;
        }
 
        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
        public struct CERT_PUBLIC_KEY_INFO
        {
            public CRYPT_ALGORITHM_IDENTIFIER Algorithm;
            public CRYPTOAPI_BLOB PublicKey;
        }
 
        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
        public struct CERT_EXTENSION
        {
            [MarshalAs(UnmanagedType.LPStr)]
            public string pszObjId;
            public bool fCritical;
            public CRYPTOAPI_BLOB Value;
        }
 
        [StructLayout(LayoutKind.Sequential)]
        public struct CERT_CONTEXT
        {
            public uint dwCertEncodingType;
            public IntPtr pbCertEncoded;
            public uint cbCertEncoded;
            public IntPtr pCertInfo;
            public IntPtr hCertStore;
        }
 
        public struct CERT_INFO
        {
            public int dwVersion;
            public CRYPTOAPI_BLOB SerialNumber;
            public CRYPT_ALGORITHM_IDENTIFIER SignatureAlgorithm;
            public CRYPTOAPI_BLOB Issuer;
            public FILETIME NotBefore;
            public FILETIME NotAfter;
            public CRYPTOAPI_BLOB Subject;
            public CERT_PUBLIC_KEY_INFO SubjectPublicKeyInfo;
            public CRYPTOAPI_BLOB IssuerUniqueId;
            public CRYPTOAPI_BLOB SubjectUniqueId;
            public int cExtension;
            public CERT_EXTENSION rgExtension;
        }
 
        [StructLayout(LayoutKind.Sequential)]
        public struct CRL_CONTEXT
        {
            public Int32 dwCertEncodingType;
            public IntPtr pbCrlEncoded;
            public Int32 cbCrlEncoded;
            public IntPtr pCrlInfo;
            public IntPtr hCertStore;
        }
 
        [StructLayout(LayoutKind.Sequential)]
        public struct CRL_INFO
        {
            public Int32 dwVersion;
            public CRYPT_ALGORITHM_IDENTIFIER SignatureAlgorithm;
            public CRYPTOAPI_BLOB Issuer;
            public FILETIME ThisUpdate;
            public FILETIME NextUpdate;
            public Int32 cCRLEntry;
            public IntPtr rgCRLEntry;
            public Int32 cExtension;
            public IntPtr rgExtension;
        }
 
        [StructLayout(LayoutKind.Sequential)]
        public struct CRYPT_ALGORITHM_IDENTIFIER
        {
            [MarshalAs(UnmanagedType.LPStr)]
            public String pszObjId;
            public CRYPTOAPI_BLOB Parameters;
        }
 
        [StructLayout(LayoutKind.Sequential)]
        public struct CRYPTOAPI_BLOB
        {
            public Int32 cbData;
            public IntPtr pbData;
        }
 
        [StructLayout(LayoutKind.Sequential)]
        public struct FILETIME
        {
            public Int32 dwLowDateTime;
            public Int32 dwHighDateTime;
        }
 
        [StructLayout(LayoutKind.Sequential)]
        public struct CRL_ENTRY
        {
            public CRYPTOAPI_BLOB SerialNumber;
            public FILETIME RevocationDate;
            public Int32 cExtension;
            public IntPtr rgExtension;
        }
 
        #endregion Structs
 
        #region Consts
 
        public const Int32 CERT_QUERY_OBJECT_FILE = 0x00000001;
        public const Int32 CERT_QUERY_OBJECT_BLOB = 0x00000002;
        public const Int32 CERT_QUERY_CONTENT_CRL = 3;
        public const Int32 CERT_QUERY_CONTENT_FLAG_CRL = 1 << CERT_QUERY_CONTENT_CRL;
        public const Int32 CERT_QUERY_FORMAT_BINARY = 1;
        public const Int32 CERT_QUERY_FORMAT_BASE64_ENCODED = 2;
        public const Int32 CERT_QUERY_FORMAT_ASN_ASCII_HEX_ENCODED = 3;
        public const Int32 CERT_QUERY_FORMAT_FLAG_BINARY = 1 << CERT_QUERY_FORMAT_BINARY;
        public const Int32 CERT_QUERY_FORMAT_FLAG_BASE64_ENCODED = 1 << CERT_QUERY_FORMAT_BASE64_ENCODED;
        public const Int32 CERT_QUERY_FORMAT_FLAG_ASN_ASCII_HEX_ENCODED = 1 << CERT_QUERY_FORMAT_ASN_ASCII_HEX_ENCODED;
        public const Int32 CERT_QUERY_FORMAT_FLAG_ALL = CERT_QUERY_FORMAT_FLAG_BINARY | CERT_QUERY_FORMAT_FLAG_BASE64_ENCODED | CERT_QUERY_FORMAT_FLAG_ASN_ASCII_HEX_ENCODED;
 
        public const Int32 X509_ASN_ENCODING = 0x00000001;
        public const Int32 PKCS_7_ASN_ENCODING = 0x00010000;
 
        public const Int32 X509_NAME = 7;
 
        public const Int32 CERT_SIMPLE_NAME_STR = 1;
        public const Int32 CERT_OID_NAME_STR = 2;
        public const Int32 CERT_X500_NAME_STR = 3;
 
        public const String szOID_CRL_REASON_CODE = "2.5.29.21";
 
        public enum Disposition : uint
        {
            CERT_STORE_ADD_NEW = 1,
            CERT_STORE_ADD_USE_EXISTING = 2,
            CERT_STORE_ADD_REPLACE_EXISTING = 3,
            CERT_STORE_ADD_ALWAYS = 4,
            CERT_STORE_ADD_REPLACE_EXISTING_INHERIT_PROPERTIES = 5,
            CERT_STORE_ADD_NEWER = 6,
            CERT_STORE_ADD_NEWER_INHERIT_PROPERTIES = 7,
        }
 
        [Flags]
        public enum FindFlags : int
        {
            CRL_FIND_ISSUED_BY_AKI_FLAG = 0x1,
            CRL_FIND_ISSUED_BY_SIGNATURE_FLAG = 0x2,
            CRL_FIND_ISSUED_BY_DELTA_FLAG = 0x4,
            CRL_FIND_ISSUED_BY_BASE_FLAG = 0x8,
        }
 
        public enum FindType : int
        {
            CRL_FIND_ANY = 0,
            CRL_FIND_ISSUED_BY = 1,
            CRL_FIND_EXISTING = 2,
            CRL_FIND_ISSUED_FOR = 3
        }
 
        #endregion
    }