C# 4.0 CheckSignature（密钥）总是抛出错误

我对C#NET编程还不熟悉。在在线参考的帮助下，我编写了下面的代码来验证SAML断言（由服务器API生成）的签名

我的环境：
VS 2010版本4.0 赢XP SP3

SAML断言令牌如下所示：

<saml:Assertion xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion" Version="2.0" ID="idGYEv...USb8GfnqF" IssueInstant="2012-12-05T14:13:39.00Z">
<saml:Issuer Format="urn:oasis:names:tc:SAML:2.0:nameid-format:entity">http://noszti...xyz.com</saml:Issuer>
<Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
<SignedInfo>
<CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
<SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1"/>
<Reference URI="">
<Transforms>
<Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/>
</Transforms>
<DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
<DigestValue>uDeAjOE/iCa6Pfz5oOjaOMtAQe4=</DigestValue>
</Reference>
</SignedInfo>
<SignatureValue>IGjZX...LaEMzA=</SignatureValue>
<KeyInfo>
<X509Data>


<X509Certificate>MIIE...cg6A==</X509Certificate>
<X509SubjectName>emailAddress=xmlsec@aleksey.com,CN=Aleksey Sanin,OU=Test Root Certificate,O=XML Security Library (http://www.aleksey.com/xmlsec),ST=California,C=US</X509SubjectName>
</X509Data>
</KeyInfo>
</Signature>
<saml:Subject>
<saml:NameID Format="urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified">admin</saml:NameID>
<saml:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer">
<saml:SubjectConfirmationData NotOnOrAfter="2012-12-05T14:19:39.00Z" Recipient=""/>
</saml:SubjectConfirmation>
</saml:Subject>
<saml:Conditions NotBefore="2012-12-05T14:13:39.00Z" NotOnOrAfter="2012-12-05T14:19:39.00Z">
<saml:AudienceRestriction>
<saml:Audience/>
</saml:AudienceRestriction>
</saml:Conditions>
<saml:AuthnStatement AuthnInstant="2012-12-05T14:13:39.00Z">
<saml:AuthnContext>
<saml:AuthnContextClassRef>urn:oasis:names:tc:SAML:2.0:ac:classes:Password</saml:AuthnContextClassRef>
</saml:AuthnContext>
</saml:AuthnStatement>
</saml:Assertion>

---

在运行代码时，它抛出一个错误“无法为提供的签名算法创建SignatureDescription” 在线：bool-verified=sig.CheckSignature（rsaKey）

调试时，签名被正确分配给SigElm。 注意：从“X509Certificate.cer”检索到的证书与签名元素（在SAML断言中）中显示的证书完全相同。因此，它看起来像是一个有效且匹配的证书。SAML断言令牌中的证书使用私钥签名；因此，我使用“X509Certificate.cer”（最终用户可用的证书）中的公钥来验证签名（在SAML断言中）

我还尝试使用以下方法验证签名： bool-verified=sig.CheckSignature（X509Cert，true）； 但它抛出了同样的错误

我尝试了几种方法（使用此错误的在线参考），但无法解决问题

请告知

//Load the SAMLAssertionToken in XML Document
XmlDocument xDoc = new XmlDocument();
xDoc.PreserveWhitespace = false;
xDoc.LoadXml(SAMLAssertionToken); //SAMLAssertionToken above
//Retrieve the public key from certificate available to end user
X509Certificate2 X509Cert = new X509Certificate2("D:/Schemas/X509Certificate.cer");
RSACryptoServiceProvider rsaKey = (RSACryptoServiceProvider)X509Cert.PublicKey.Key;
//Signature Verification Starts. Find the Signature element
XmlNamespaceManager xMan = new XmlNamespaceManager(xDoc.NameTable);
xMan.AddNamespace("ns", "urn:oasis:names:tc:SAML:2.0:assertion");
xMan.AddNamespace("ns1", "http://www.w3.org/2000/09/xmldsig#");
XmlElement SigElm = (XmlElement)xDoc.SelectSingleNode("//ns:Assertion//ns1:Signature", xMan);
//Create SignedXml object and load signature for verification
SignedXml sig = new SignedXml(xDoc);                
sig.LoadXml(SigElm);
bool verified = sig.CheckSignature(rsaKey);
if (verified)
    {                    
        Console.WriteLine("Signature verified successfully");
    }
else
    {
        Console.WriteLine("Signature not valid");
    }