Webservices. XML Signature und XML Processing. Meiko Jensen, Juraj Somorovsky, Jörg Schwenk Lehrstuhl für Netz- und Datensicherheit

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1 Master-Praktikum zur Programmierung sicherer Webservices XML Signature und XML Processing

2 WS-SecuritySecurity Transport-level security VS Message-level security Client Web Service Action Server Web Service Payment Server

3 XML Signature Ensures Integrity and authenticity of exchanged XML messages ( Three types: Enveloping Enveloped Detached

4 XML Signature <soapenv:envelope xmlns:soapenv=".../soap/envelope/"> <soapenv:header> <ds:signature Id="Signature-3" xmlns:ds=" /xmldsig#"> <ds:signedinfo> <ds:canonicalizationmethod Algorithm=".../xml-exc-c14n#"/> <ds:signaturemethod Algorithm=" /xmldsig#rsa-sha1"/> g <ds:reference URI="#1"> <ds:transforms> <ds:transform Algorithm=" /xml-exc-c14n#"/> </ds:transforms> <ds:digestmethod Algorithm=" xmldsig#sha1"/> <ds:digestvalue>sdbsy =</ds:digestvalue> </ds:reference> </ds:signedinfo> <ds:signaturevalue>fl1y...8=</ds:signaturevalue> <ds:keyinfo>...</ds:keyinfo> </ds:signature> </soapenv:header> <soapenv:body wsu:id="1">... </soapenv:body> </soapenv:envelope> Envelope Header Signature SignedInfo Reference URI="#1" SignatureValue KeyInfo Body Id= 1

5 XML Signature Verifikation 1. Verifikation der <Reference>-Elemente a) Lade die Ressource, die durch die URI in dem <Reference>-Element spezifiziert ist. b) Wende auf jede Ressource die in <Transforms> spezifizierten Transformationen an. c) Berechne den Hashwert mit dem in <DigestMethod> angegebenen Algorithmus. d) Vergleiche das Ergebnis mit dem Wert des <DigestValue>-Elements. Wenn die Werte nicht übereinstimmen, ist die Signatur ungültig. 2. Verifikation der Signatur a) Kanonisierte das gesamte <SignedInfo>-Element durch Anwendung <CanonicalizationMethod> b) Berechne den Hashwert des kanonisierten <SignedInfo>-Elements mittels <SignatureMethod> c) Verifiziere die Signatur aus <SignatureValue> gegen diesen Hashwert.

6 XML Signature Das <SignedInfo>-Element hat drei oder mehr Nachfolger <CanonicalizationMethod>: gewährleistet, XML-Dokumente mit gleicher Semantik die gleiche Signatur liefern: <SignatureMethod>: spezifiziert den Hash- und Signaturalgorithmus (z.b. DSAwithSHA1, RSAwithSHA1) Ein oder mehrere <Reference>-Elemente: enthält <Transform>, <DigestMethod>, <DigestValue> Das <SignatureValue>-Element enthält die Base64-Codierung der eigentlichen Signatur Das <KeyInfo>-Element referenziert den Schlüssel zur Überprüfung fehlt: keine Information zum Schlüssel. enthält <KeyName>: eindeutiger Name des Schlüssels. enthält <KeyValue>: enthält als Nachfolger entweder <DSAKeyValue> oder <RSAKeyValue> enthält <RetrievalMethod>: Eine URI, wo der Schlüssel zu finden ist

7 XML Canonicalization Codierung in UTF-8 Zeilenumbrüche einheitlich als 0x0A Attribute werden normalisiert Leere Elemente werden in Start-Ende-Paare umgewandelt Namespaces werden kanonisiert Beispiel ( +cr+ Carriage Return, +lf+ Line Feed): <?xml version="1.0"?> +cr++lf+ <Liste id = 123 > +cr++lf+ <Element1> Hallo </Element1>+cr++lf+ <Element2/>+cr++lf+ </Liste>+cr++lf+ <Liste id="123"> +lf+ <Element1> Hallo </Element1>+lf+ <Element2></Element2>+lf+ </Liste>+lf+

8 Namespaces Canonicalization <ds:signature xmlns:ds= <ds:signedinfo>... </ds:signedinfo> </ds:signature> Inclusive XML Canonicalization: outputs directly each namespace, which was not already declared <n0:pdu xmlns:n0=" <n1:elem1 xmlns:n1=" content </n1:elem1> </n0:pdu> <n1:elem1 xmlns:n1=" content </n1:elem1> <n1:elem1 xmlns:n0=" xmlns:n1=" content </n1:elem1>

9 Namespaces Canonicalization Exclusive XML Canonicalization outputs namespace only if: Which h was not already declared d by ancestors The element visibly utilizes the namespace (element or its attributes use this namespace) <n0:pdu xmlns:n0=" <n1:elem1 xmlns:n1=" content </n1:elem1> </n0:pdu> <n1:elem1 xmlns:n1=" p content </n1:elem1> <n1:elem1 xmlns:n1=" content </n1:elem1>

10 Schlüssel-Erstellung JDK keytool Key-Generierung: keytool -genkey -v -keyalg RSA -alias <my-alias> -keypass <keypass> -storepass <storepass> -dname "CN=<name>, OU=NDS, O=RUB, L=Bochum, S=NRW, C=DE -keystore <file> alias Name des Keystore-Eintrags keypass Passwort für das Schlüsselpaar storepass Passwort für den gesamten Keystore Anzeige der Key-Daten keytool -list -v -storepass <storepass> Quellen:

11 XML Signature in SOAPUI

14 XML Processing DOM W3C-Standard, Eingesetzt in den meisten Frameworks DOM stellt XML-Dokumente als Baumstruktur dar Flexibel aber nicht Speicher-schonend (in Java: 4MB Dokument, Elemente 80 MB Speicher) <library> <book> <author>sierra, Bates</author> <title>scjp</title> <year>2008</year> </book> <book> <author> </author> <title> </title> <year> </year> </book> </library> book library book author title year author title year

15 XML Processing DOM in Java String filename = "Library.xml"; try { // create validating document builder factory DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); // parse XML tree into DOM document tree DocumentBuilder builder = factory.newdocumentbuilder(); Document document = builder.parse(filename); // create node list NodeList nodelist = document.getelementsbytagname("title"); for (int i = 0; i < nodelist.getlength(); g i++) { Node node = nodelist.item(i); // print text System.out.println(node.getTextContent()); // print attributes NamedNodeMap attrs = node.getattributes(); for(int j=0; j<attrs.getlength(); j++) { System.out.println(attrs.item(j).toString()); } } } catch (Exception e) { e.printstacktrace(); } // Libraries: import javax.xml.parsers.documentbuilder; import javax.xml.parsers.documentbuilderfactory; import org.w3c.dom.document; import org.w3c.dom.namednodemap; import org.w3c.dom.node; import org.w3c.dom.nodelist;

16 Attacks against Web Service Servers Recursive Payloads: An attacker tries to break a Web Service server sending XML documents that t are very deep nested Oversize Payloads: consists of creating large SOAP messages with many elements XML Entity Expansions: <!DOCTYPE foo [ <!ENTITY a " " > <!ENTITY b "&a;&a;" > <!ENTITY c "&b;&b;" > ]> <foo>&c;</foo> Canonicalization Processing: 1) <foo>&b;&b;</foo> 2) <foo>&a;&a;&a;&a;</foo> 3) <foo> </foo>

17 Attacks against Web Service Servers Modified SOAP message with XML Signature: costly signature verifications Encrypted large blocks: Recursive and Oversize Payload attacks could be detected t d with a message schema validation. However, it is not possible when the message is encrypted.

18 Streaming-based XML Processing Also called Event-based processing based on events Advantages in memory consumption Requeire much more skilled application design SAX and StAX (Push and Pull parsing) Examples: LIBXML2 Stream Pull-Parser Java 1.5 Default SAX (Java) Woodstox StAX Pull-Parser Sun SJSXP StAX Pull-Parser BEA StAX implementation Oracle StAX implementation XDK

19 Event-based XML processing Use of SAX, StAX Example <university name= RUB > <location> Bochum </location> </university> startelement() -qname: university -parameter name= RUB startelement() -qname: location characters() -char: Bochum endelement() -qname: location endelement() -qname: university

20 SAX vs StAX SAX Simple API for XML StAX Streaming API for XML SAX (push-parsing): the XML parser sends (pushes) all available XML data to the client ( StAX (pull-parsing): the client only gets (pulls) XML data when it explicitly asks for it StAX advantages: Control over the thread Can read multiple documents at once with a single thread Supports writing to the document

21 SAX Design XMLReaderFactory: Class instantiating a class implementing an XMLReader XMLReader: Interface parsing input data ContentHandler: Interface for document parsing events ErrorHandler: Interface for handling errors and warnings DTDHandler: Interface for handling DTD DefaultHandler: Class implementing handler interfaces. All its events return default null values. To add a concrete behavior for XML document parsing this class must be extended MyHandler

22 SAX Example public class MyHandler extends DefaultHandler { public void startdocument() { System.out.println("Document Started"); } public void startelement(string uri, String name, String qname, Attributes atts) { if ("".equals(uri)) System.out.println("Start element: " + qname); else System.out.println("Start element: {" + uri + "}" + name); } public void characters(char ch[], int start, int length) { System.out.println("Characters: " + new String(ch, start, length)); } } public void endelement(string uri, String name, String qname) { System.out.println("End element: " + qname); } // Libraries: import org.xml.sax.attributes; import org.xml.sax.helpers.defaulthandler;

23 SAX Example public class Main { } public static void main(string[] args) { } try { // create XMLReader XMLReader xr = XMLReaderFactory.createXMLReader(); t d // set the ContentHandler xr.setcontenthandler(new MyHandler()); // Parse the file xr.parse("library.xml"); } catch (IOException ioe) { ioe.printstacktrace(); } catch (SAXException saxe) { saxe.printstacktrace(); } // Libraries: import java.io.ioexception; import org.xml.sax.saxexception; import org.xml.sax.xmlreader; import org.xml.sax.helpers.xmlreaderfactory;

24 StAX Example (reading) public static void main(string[] args) { try { InputStream inputstream = new FileInputStream("Library.xml"); XMLInputFactory factory = XMLInputFactory.newInstance(); XMLStreamReader reader = factory.createxmlstreamreader(inputstream); while (reader.hasnext()) { switch (reader.next()) { PULL case XMLStreamConstants.START_ELEMENT: System.out.print(reader.getName()); p ( g ()); if (reader.getattributecount() > 0) System.out.print(" : " + reader.getattributevalue(0)); break; case XMLStreamConstants.END_ELEMENT: ELEMENT: System.out.print(reader.getName()); break; case XMLStreamConstants.CHARACTERS: System.out.print(reader.getText()); break; } } } catch (Exception e) {... } } // Libraries: import java.io.fileinputstream; import java.io.inputstream; import javax.xml.stream.xmlinputfactory; xml import javax.xml.stream.xmlstreamconstants; import javax.xml.stream.xmlstreamexception; import javax.xml.stream.xmlstreamreader;

25 StAX Example (writing) public static void main(string[] args) { try { FileOutputStream fos = new FileOutputStream("output.xml"); XMLOutputFactory factory = XMLOutputFactory.newInstance(); XMLStreamWriter outwriter = factory.createxmlstreamwriter(fos); } outwriter.writestartdocument("1.0"); // <?xml version="1.0"?> outwriter.writestartelement("e1"); // <e1> outwriter.writeattribute("id", ib t "x");") // <... id= x > > outwriter.writecharacters("hallo"); // hallo outwriter.writecomment("comment"); //  outwriter.writeendelement(); outwriter.close(); } catch (FileNotFoundException e) { e.printstacktrace(); } catch (XMLStreamException e) { e.printstacktrace(); } // Libraries: import java.io.filenotfoundexception; import java.io.fileoutputstream; import javax.xml.stream.xmloutputfactory; xml import javax.xml.stream.xmlstreamexception; import javax.xml.stream.xmlstreamwriter;

26 Streaming-based XML Signature Processing

27 Streaming-based XML Signature Processing Problems: Referencing of already parsed elements (typically Timestamps, Username Tokens) XPath Backward Referencing: /Envelope/Body/Element/parent::Body XML Signature Creation XSLT-Transformations

28 Streaming-based XML Signature Validation (Project) <soapenv:envelope xmlns:soapenv=".../soap/envelope/"> <soapenv:header> <ds:signature Id="Signature-3" xmlns:ds=" /xmldsig#"> <ds:signedinfo> <ds:canonicalizationmethod Algorithm=".../xml-exc-c14n#"/> <ds:signaturemethod Algorithm=" /xmldsig#rsa-sha1"/> g <ds:reference URI="#1"> <ds:transforms> <ds:transform Algorithm=" /xml-exc-c14n#"/> </ds:transforms> <ds:digestmethod Algorithm=" xmldsig#sha1"/> <ds:digestvalue>sdbsy =</ds:digestvalue> </ds:reference> </ds:signedinfo> <ds:signaturevalue>fl1y...8=</ds:signaturevalue> <ds:keyinfo>...</ds:keyinfo> </ds:signature> </soapenv:header> <soapenv:body wsu:id="1">... </soapenv:body> </soapenv:envelope> Begin digest value computation Read signature method Read Reference URI Read Digest algorithm and value End digest value computation Apply signature algorithm to the digest value and verify Compute digest value of the Reference and verify

29 Next time Java Security Design Patterns

30 XML Processing Quellen html MLDigitalSignature.html#wp512158it t l# 1.html