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Secure Web Services

Secure Web Services. Arvind Easwaran (arvinde@seas) CIS/TCOM 551 Spring 2004 Slide Set 7. Outline. Web Services (WS): An overview XML Basics SOAP Basics WSEmail : The real one Security in WS. Web Services (WS) Overview. Today’s Web.

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Secure Web Services

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  1. Secure Web Services Arvind Easwaran (arvinde@seas) CIS/TCOM 551 Spring 2004 Slide Set 7

  2. Outline • Web Services (WS): An overview • XML Basics • SOAP Basics • WSEmail : The real one • Security in WS

  3. Web Services (WS) Overview

  4. Today’s Web • Designed for applications involving human interactions • Intended purpose • Information sharing: a distributed content library • Enabled B2C e-commerce • Non-automated B2B interactions • How did it happen? • Built on very few standards: http + html • Shallow interaction model: very few assumptions • Result was ubiquity

  5. What’s next? • There is a lot more we can do ! • Open, automated B2B e-commerce • Business process integration on the Web • Resource sharing, distributed computing • Existing Web technology is ad hoc for this • Application-to-application interactions with HTML forms • Goal Enabling systematic application-to-application interaction on the Web

  6. Web Services “Web services” is an effort to build a distributed computing platform for the Web Web service applications are encapsulated, loosely coupled Web “components” that can bind dynamically to each other The Penn – Amazon example

  7. Typical Web Service Components

  8. Web Service A programmable application component accessible via standard Web protocols Open Internet Protocols UDDI Universal Description, Discovery, and Integration • Provide a Directory of Services on the Internet WSDL Web Services Description Language • Web Services are defined in terms of the formats and ordering of messages SOAP • Web Services consumers send and receive SOAP messages XML & HTTP • Built using open Internet protocols Web Services Architecture

  9. Web Services Framework • Framework can be described in terms of • What goes “on the wire” Formats and protocols : XML and SOAP using HTTP • What describes what goes on the wire Description languages : WSDL • What allows us to find these descriptions Discovery of services : UDDI

  10. XML

  11. What is XML? • Extensible Markup Language • Meta language that • Allows to create and format own document markups • a method for putting structured data into a text file - easy to read - unambiguous - extensible - platform-independent

  12. Sample XML Example <?xml version=“1.0” encoding=“…”?> <msg:message from=“id” to=“id” xmlns:msg=“URI” xmlns:po=“URI”> <msg:text> Hi please bill to the following address </msg:text> <msg:item> <po:po id=“123”> <po:billto> <po:company> Skateboard </po:company> <po:street> One Warehouse Park </po:street> <po:city> Boston </po:city> </po:billto> </po:po> </msg:item> </msg:message>

  13. XML Declaration <?xml version=“1.0” encoding=“…”?> • <?xml ?> the XML declaration • Not required, but typically used • Attributes include: • Version • Encoding – the character encoding

  14. XML Element <msg:message from=“id” to=“id” xmlns:msg=“URI” xmlns:po=“URI”> <msg:text> Hi please bill the following </msg:text> <msg:item> <po:po id=“123”> … </po:po> </msg:item> </msg:message> • <tag> text/element </tag> an element • Each element tag can be divided into 2 parts  Namespace, Tag name

  15. XML Attribute <msg:message from=“id” to=“id” xmlns:msg=“URI” xmlns:po=“URI”> … <po:po id=“123”> … </po:po> </msg:message> • XML Attribute • Describes additional information about an element • <tag key=”value”> text</tag> • Reserved attribute  xml:lang

  16. XML Namespaces <msg:message from=“id” to=“id” xmlns:msg=“URI” xmlns:po=“URI”> … </msg:message> • Namespaces • Not mandatory, but useful in giving uniqueness to an element • Declared using the xmlns:name= “value”

  17. SOAP

  18. SOAP • An XML envelope for XML messaging • Headers + body • SOAP is “transport independent” • A convention for doing RPC

  19. Soap Message Processing

  20. SOAP Message Example <?xml … ?> <SOAP-ENV:Envelope xmlns:SOAP-ENV=“URI” > <SOAP-ENV:Header> <t:Transaction xmlns:t=“URI” SOAP-ENV:mustUnderstand=“1” > 12345 </t:Transaction> <p:Priority xmlns:p=“URI”> Very High </p:Priority> </SOAP-ENV:Header> <SOAP-ENV:Body> “XML Document” </SOAP-ENV:Body> </SOAP-ENV:Envelope>

  21. WSEmail Carl Gunter Kevin Lux Michael May

  22. WSEmail • Traditional Internet Email • Based on a collection of protocols • SMTP, POP, IMAP • Evolved over a vast installed base • Shortcomings • Flexibility • Security and • Integration

  23. WSEmail : The Solution • Aims to exploit advantages of web service protocols • Uses web service security features to support integrity, authentication, and access control for both end-to-end and hop-by-hop message transmissions • A collection of services that can be added to the base system

  24. The Solution (Contd) • A way to integrate different messaging systems • Prototype system is built using Microsoft .Net • On-demand attachments • Integrated instant messaging

  25. Architecture

  26. Architecture (Contd) • Sender Client SC makes a call on its Sender Server SS • All calls are SOAP calls over TCP • The server SS then makes a call on the Receiver Server RS • The Receiver Client RC periodically makes calls to RC • Security based on standards for web service security possibly supported by encrypted tunnels

  27. Architecture (Contd) • Hop-by-hop confidentiality, so communications between the nodes can be protected by TLS • Clients like SC and RC are typically authenticated by a password • Servers authenticate themselves using certificates • Such certificates are used in TLS and used to sign messages using XMLDSIG

  28. Variations – Security Token

  29. Security Token (Contd) • SC contacts SS to obtain a security token recognized by RS • SC sends a message authenticated with this credential to RS • Instant messages are posted directly to the client • RS and RC apply access control for this function based on the security token from SC • Token is recognized because of a form of federated identity between SS and RS

  30. Security

  31. Why Web Services Security is a Challenge Practice: In this environment we need 4 wheel drive Theory: This thing has 4 wheel drive But we only take it to the Mall

  32. Message Level Security

  33. Example : SC to SS <wsse:Security SOAP-ENV:mustUnderstand="1“ SOAP-ENV:actor=“…” xmlns:wsse=“…"> <wsse:UsernameToken xmlns:wsu=“…“ wsu:Id="SecurityToken…"> <wsse:Username>SC</wsse:Username> <wsse:Nonce>…</wsse:Nonce> <wsu:Created>Date</wsu:Created> </wsse:UsernameToken>

  34. <Signature> <SignedInfo> <CanonicalizationMethod Algorithm=“…" /> <SignatureMethod Algorithm=“hmac- sha1" /> <Reference URI="#Id…"> <Transforms> <Transform Algorithm="xml-exc-c14n#" /> </Transforms> <DigestMethod Algorithm="xmldsig#sha1" /> <DigestValue>…</DigestValue> </Reference> </SignedInfo>

  35. <SignatureValue>…</SignatureValue> <KeyInfo> <wsse:SecurityTokenReference> <wsse:Reference URI=“…" /> </wsse:SecurityTokenReference> </KeyInfo> </Signature> </wsse:Security>

  36. Canonicalization • Logically equivalent physically different XML snippets • <p a=“1” b=“2”> </p> • <p a=“1” b=“2” />

  37. XML Element Specific Security <po xmlns=“URI” id=“123”> <enc:EncryptedData Type=“URI”> <enc:EncryptionMethod Algorithm=“…”/> <ds:KeyInfo> <ds:KeyName> Shared Key </ds:KeyName> </ds:KeyInfo> <enc:CipherData>…</enc:CipherData> </enc:EncryptedData> … </po>

  38. XML Key Management Specification (XKMS) • Management of Public Keys • Registration • Alice registers her email signature public key • Information • Bob looks up the key for Alice • Bob checks to see if it is valid • Core Objective • Shield the client from the complexity of PKI

  39. Platform Level Security

  40. Security Terminology • Authentication • Positively identifying the clients • User ID password pairs, X509 certificate etc • Authorization • Defining what authenticated clients are allowed to see and do • ACLs • Non Repudiation • Digital Signatures • Secure Communication • Ensuring that messages remain private and unaltered as they cross networks • SSL point-to-point

  41. Is SSL Alone Enough? • For some applications  Yes • As Infrastructure  No • SSL does not support multi-party transactions • Intermediate Node • SSL does not support non-Repudiation • Does not leave any audit trail

  42. Demo

  43. Conclusions • Without Security and Trust • Web Services are Dead On Arrival • Considerable progress has already been made • Industry wide consensus on value of standards • Basic Infrastructure is in place or in development • There is considerable consensus on the roadmap • Web Services is certainly moving towards a secure architecture

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