Unity3d HTTPS Get with X509Certificate P12

Hi i want to do a http get attaching a X509Certificate P12 that i load from a file in the storage. The code i attached WORKS well in pure mono and c#, but in unity i got this problem:

NotSupportedException: Undefined length encoding. Mono.Security.ASN1..ctor (System.Byte[] data) (at /Users/builduser/buildslave/monoAndRuntimeClassLibs/build/mcs/class/corlib/Mono.Security/ASN1.cs:82) Mono.Security.X509.X509Certificate.Parse (System.Byte[] data) (at /Users/builduser/buildslave/monoAndRuntimeClassLibs/build/mcs/class/corlib/Mono.Security.X509/X509Certificate.cs:109) Rethrow as CryptographicException: Input data cannot be coded as a valid certificate.

The code is:

         X509Certificate cert = new X509Certificate(@"D:\temp\cert.p12", "password");
 
         HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(url);
         webRequest.Method = "GET";
         webRequest.Accept = "Application/xml";
 
         webRequest.ClientCertificates.Add(cert);
 
         HttpWebResponse webResponse = (HttpWebResponse)webRequest.GetResponse();
         Debug.LogWarning("RESPONSE: " + webResponse.GetResponseStream());

I'm using Unity version 4.3.4f1, i tried it too in 4.6.3 and unity 5.0.1.