Fix X509CertificateEndpointIdentity deserialization bug causing CryptographicException

src/System.ServiceModel.Primitives/src/System/ServiceModel/X509CertificateEndpointIdentity.cs

@@ -61,8 +61,7 @@ internal X509CertificateEndpointIdentity(XmlDictionaryReader reader)
             reader.ReadStartElement(XD.XmlSignatureDictionary.X509Data, XD.XmlSignatureDictionary.Namespace);
             while (reader.IsStartElement(XD.XmlSignatureDictionary.X509Certificate, XD.XmlSignatureDictionary.Namespace))
             {
-                reader.MoveToContent();
-                X509Certificate2 certificate = new X509Certificate2(Convert.FromBase64String(reader.ReadContentAsString()));
+                X509Certificate2 certificate = new X509Certificate2(Convert.FromBase64String(reader.ReadElementString()));
                 if (Certificates.Count == 0)
                 {
                     // This is the first certificate. We assume this as the primary 

src/System.ServiceModel.Primitives/tests/ServiceModel/X509CertificateEndpointIdentityTest.cs

@@ -0,0 +1,107 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.IO;
+using System.Security.Cryptography;
+using System.Security.Cryptography.X509Certificates;
+using System.ServiceModel;
+using System.Xml;
+using Infrastructure.Common;
+using Xunit;
+
+public class X509CertificateEndpointIdentityTest : ConditionalWcfTest
+{
+    [WcfFact]
+    [Issue(3572, OS = OSID.OSX)]
+    public static void X509Certificate_RoundTrip_Succeeds()
+    {
+        // Create a self-signed certificate for testing
+        X509Certificate2 certificate = CreateTestCertificate();
+
+        // Manually construct the XML that would be sent from the server
+        // This ensures we're testing deserialization independently of WriteContentsTo
+        string certificateBase64 = Convert.ToBase64String(certificate.RawData);
+        string xml = $@"<Identity xmlns=""http://schemas.xmlsoap.org/ws/2006/02/addressingidentity"">
+    <KeyInfo xmlns=""http://www.w3.org/2000/09/xmldsig#"">
+        <X509Data>
+            <X509Certificate>{certificateBase64}</X509Certificate>
+        </X509Data>
+    </KeyInfo>
+</Identity>";
+
+        // Deserialize from XML
+        X509CertificateEndpointIdentity deserializedIdentity;
+        using (var reader = XmlReader.Create(new StringReader(xml)))
+        {
+            // This uses the internal constructor that reads from XmlDictionaryReader
+            // ReadIdentity expects to read the Identity element and its contents
+            deserializedIdentity = (X509CertificateEndpointIdentity)typeof(EndpointIdentity)
+                .GetMethod("ReadIdentity", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Static)
+                .Invoke(null, new object[] { XmlDictionaryReader.CreateDictionaryReader(reader) });
+        }
+
+        // Verify the certificate was correctly deserialized
+        Assert.NotNull(deserializedIdentity);
+        X509Certificate2 deserializedCert = Assert.Single(deserializedIdentity.Certificates);
+        Assert.Equal(certificate.Thumbprint, deserializedCert.Thumbprint);
+        Assert.Equal(certificate.GetCertHash(), deserializedCert.GetCertHash());
+    }
+
+    [WcfFact]
+    [Issue(3572, OS = OSID.OSX)]
+    public static void X509Certificate_Multiple_RoundTrip_Succeeds()
+    {
+        // Create two test certificates
+        X509Certificate2 primaryCert = CreateTestCertificate();
+        X509Certificate2 supportingCert = CreateTestCertificate();
+
+        // Manually construct the XML that would be sent from the server with multiple certificates
+        // This ensures we're testing deserialization independently of WriteContentsTo
+        string primaryCertBase64 = Convert.ToBase64String(primaryCert.RawData);
+        string supportingCertBase64 = Convert.ToBase64String(supportingCert.RawData);
+        string xml = $@"<Identity xmlns=""http://schemas.xmlsoap.org/ws/2006/02/addressingidentity"">
+    <KeyInfo xmlns=""http://www.w3.org/2000/09/xmldsig#"">
+        <X509Data>
+            <X509Certificate>{primaryCertBase64}</X509Certificate>
+            <X509Certificate>{supportingCertBase64}</X509Certificate>
+        </X509Data>
+    </KeyInfo>
+</Identity>";
+
+        // Deserialize from XML
+        X509CertificateEndpointIdentity deserializedIdentity;
+        using (var reader = XmlReader.Create(new StringReader(xml)))
+        {
+            // This uses the internal constructor that reads from XmlDictionaryReader
+            // ReadIdentity expects to read the Identity element and its contents
+            deserializedIdentity = (X509CertificateEndpointIdentity)typeof(EndpointIdentity)
+                .GetMethod("ReadIdentity", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Static)
+                .Invoke(null, new object[] { XmlDictionaryReader.CreateDictionaryReader(reader) });
+        }
+
+        // Verify both certificates were correctly deserialized
+        Assert.NotNull(deserializedIdentity);
+        Assert.Equal(2, deserializedIdentity.Certificates.Count);
+        Assert.Equal(primaryCert.Thumbprint, deserializedIdentity.Certificates[0].Thumbprint);
+        Assert.Equal(supportingCert.Thumbprint, deserializedIdentity.Certificates[1].Thumbprint);
+    }
+
+    private static X509Certificate2 CreateTestCertificate()
+    {
+        // Create a simple self-signed certificate for testing
+        using (RSA rsa = RSA.Create(2048))
+        {
+            var request = new CertificateRequest(
+                "CN=Test Certificate",
+                rsa,
+                HashAlgorithmName.SHA256,
+                RSASignaturePadding.Pkcs1);
+
+            return request.CreateSelfSigned(
+                DateTimeOffset.UtcNow.AddDays(-1),
+                DateTimeOffset.UtcNow.AddDays(365));
+        }
+    }
+}