I've been having this problem for a while and it's driving me nuts. I'm trying to create a client (in C# .NET 2.0) that will use SAML 1.1 to sign on to a WebLogic 10.0 server (i.e., a Single Sign-On scenario, using browser/post profile). The client is on a WinXP machine and the WebLogic server is on a RHEL 5 box. I based my client largely on code in the example here: http://www.codeproject.com/KB/aspnet/DotNetSamlPost.aspx (the source has a section for SAML 1.1). I set up WebLogic based on instructions for SAML Destination Site from here:http://www.oracle.com/technology/pub/articles/dev2arch/2006/12/sso-with-saml4.html I created a certificate using makecert that came with VS 2005. makecert -r -pe -n "CN=whatever" -b 01/01/2010 -e 01/01/2011 -sky exchange whatever.cer -sv whatever.pvk pvk2pfx.exe -pvk whatever.pvk -spc whatever.cer -pfx whatever.pfx Then I installed the .pfx to my personal certificate directory, and installed the .cer into the WebLogic SAML Identity Asserter V2. I read on another site that formatting the response to be readable (ie, adding whitespace) to the response after signing would cause this problem, so I tried various combinations of turning on/off .Indent XMLWriterSettings and turning on/off .PreserveWhiteSpace when loading the XML document, and none of it made any difference. I've printed the SignatureValue both before the message is is encoded/sent and after it arrives/gets decoded, and they are the same. So, to be clear: the Response appears to be formed, encoded, sent, and decoded fine (I see the full Response in the WebLogic logs). WebLogic finds the certificate I want it to use, verifies that a key was supplied, gets the signed info, and then fails to validate the signature. Code: public string createResponse(Dictionary<string, string> attributes){ ResponseType response = new ResponseType(); // Create Response response.ResponseID = "_" + Guid.NewGuid().ToString(); response.MajorVersion = "1"; response.MinorVersion = "1"; response.IssueInstant = System.DateTime.UtcNow; response.Recipient = "http://theWLServer/samlacs/acs"; StatusType status = new StatusType(); status.StatusCode = new StatusCodeType(); status.StatusCode.Value = new XmlQualifiedName("Success", "urn:oasis:names:tc:SAML:1.0:protocol"); response.Status = status; // Create Assertion AssertionType assertionType = CreateSaml11Assertion(attributes); response.Assertion = new AssertionType[] {assertionType}; //Serialize XmlSerializerNamespaces ns = new XmlSerializerNamespaces(); ns.Add("samlp", "urn:oasis:names:tc:SAML:1.0:protocol"); ns.Add("saml", "urn:oasis:names:tc:SAML:1.0:assertion"); XmlSerializer responseSerializer = new XmlSerializer(response.GetType()); StringWriter stringWriter = new StringWriter(); XmlWriterSettings settings = new XmlWriterSettings(); settings.OmitXmlDeclaration = true; settings.Indent = false;//I've tried both ways, for the fun of it settings.Encoding = Encoding.UTF8; XmlWriter responseWriter = XmlTextWriter.Create(stringWriter, settings); responseSerializer.Serialize(responseWriter, response, ns); responseWriter.Close(); string samlString = stringWriter.ToString(); stringWriter.Close(); // Sign the document XmlDocument doc = new XmlDocument(); doc.PreserveWhiteSpace = true; //also tried this both ways to no avail doc.LoadXml(samlString); X509Certificate2 cert = null; X509Store store = new X509Store(StoreName.My, StoreLocation.CurrentUser); store.Open(OpenFlags.ReadOnly); X509Certificate2Collection coll = store.Certificates.Find(X509FindType.FindBySubjectDistinguishedName, "distName", true); if (coll.Count < 1) { throw new ArgumentException("Unable to locate certificate"); } cert = coll[0]; store.Close(); //this special SignDoc just overrides a function in SignedXml so //it knows to look for ResponseID rather than ID XmlElement signature = SamlHelper.SignDoc( doc, cert, "ResponseID", response.ResponseID); doc.DocumentElement.InsertBefore(signature, doc.DocumentElement.ChildNodes[0]); // Base64Encode and URL Encode byte[] base64EncodedBytes = Encoding.UTF8.GetBytes(doc.OuterXml); string returnValue = System.Convert.ToBase64String( base64EncodedBytes); return returnValue; } private AssertionType CreateSaml11Assertion(Dictionary<string, string> attributes){ AssertionType assertion = new AssertionType(); assertion.AssertionID = "_" + Guid.NewGuid().ToString(); assertion.Issuer = "madeUpValue"; assertion.MajorVersion = "1"; assertion.MinorVersion = "1"; assertion.IssueInstant = System.DateTime.UtcNow; //Not before, not after conditions ConditionsType conditions = new ConditionsType(); conditions.NotBefore = DateTime.UtcNow; conditions.NotBeforeSpecified = true; conditions.NotOnOrAfter = DateTime.UtcNow.AddMinutes(10); conditions.NotOnOrAfterSpecified = true; //Name Identifier to be used in Saml Subject NameIdentifierType nameIdentifier = new NameIdentifierType(); nameIdentifier.NameQualifier = domain.Trim(); nameIdentifier.Value = subject.Trim(); SubjectConfirmationType subjectConfirmation = new SubjectConfirmationType(); subjectConfirmation.ConfirmationMethod = new string[] { "urn:oasis:names:tc:SAML:1.0:cm:bearer" }; // // Create some SAML subject. SubjectType samlSubject = new SubjectType(); AttributeStatementType attrStatement = new AttributeStatementType(); AuthenticationStatementType authStatement = new AuthenticationStatementType(); authStatement.AuthenticationMethod = "urn:oasis:names:tc:SAML:1.0:am:password"; authStatement.AuthenticationInstant = System.DateTime.UtcNow; samlSubject.Items = new object[] { nameIdentifier, subjectConfirmation}; attrStatement.Subject = samlSubject; authStatement.Subject = samlSubject; IPHostEntry ipEntry = Dns.GetHostEntry(System.Environment.MachineName); SubjectLocalityType subjectLocality = new SubjectLocalityType(); subjectLocality.IPAddress = ipEntry.AddressList[0].ToString(); authStatement.SubjectLocality = subjectLocality; attrStatement.Attribute = new AttributeType[attributes.Count]; int i=0; // Create SAML attributes. foreach (KeyValuePair<string, string> attribute in attributes) { AttributeType attr = new AttributeType(); attr.AttributeName = attribute.Key; attr.AttributeNamespace= domain; attr.AttributeValue = new object[] {attribute.Value}; attrStatement.Attribute[i] = attr; i++; } assertion.Conditions = conditions; assertion.Items = new StatementAbstractType[] {authStatement, attrStatement}; return assertion; } private static XmlElement SignDoc(XmlDocument doc, X509Certificate2 cert2, string referenceId, string referenceValue) { // Use our own implementation of SignedXml SamlSignedXml sig = new SamlSignedXml(doc, referenceId); // Add the key to the SignedXml xmlDocument. sig.SigningKey = cert2.PrivateKey; // Create a reference to be signed. Reference reference = new Reference(); reference.Uri= String.Empty; reference.Uri = "#" + referenceValue; // Add an enveloped transformation to the reference. XmlDsigEnvelopedSignatureTransform env = new XmlDsigEnvelopedSignatureTransform(); reference.AddTransform(env); // Add the reference to the SignedXml object. sig.AddReference(reference); // Add an RSAKeyValue KeyInfo (optional; helps recipient find key to validate). KeyInfo keyInfo = new KeyInfo(); keyInfo.AddClause(new KeyInfoX509Data(cert2)); sig.KeyInfo = keyInfo; // Compute the signature. sig.ComputeSignature(); // Get the XML representation of the signature and save // it to an XmlElement object. XmlElement xmlDigitalSignature = sig.GetXml(); return xmlDigitalSignature; } To open the page in my client app, string postData = String.Format("SAMLResponse={0}&APID=ap_00001&TARGET={1}", System.Web.HttpUtility.UrlEncode(builder.buildResponse("http://theWLServer/samlacs/acs",attributes)), "http://desiredURL"); webBrowser.Navigate("http://theWLServer/samlacs/acs", "_self", Encoding.UTF8.GetBytes(postData), "Content-Type: application/x-www-form-urlencoded");