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XML, Extensible Security Markups

XML, Extensible Security Markups. Hilarie Orman PurpleStreak Development. SOAP and Security. Tolga Acar Novell, Inc. XML, Extensible Markup and Much More. Like HTML, a tagged data language <NAME>Hilarie Orman</NAME> Strictly parsed into a tree Brought to you by the W3C

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XML, Extensible Security Markups

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  1. XML, Extensible Security Markups Hilarie Orman PurpleStreak Development SOAP and Security Tolga Acar Novell, Inc.

  2. XML, Extensible Markup and Much More • Like HTML, a tagged data language • <NAME>Hilarie Orman</NAME> • Strictly parsed into a tree • Brought to you by the W3C • Widely used for database/Web page interactions • Extensibility means it can do just about anything • Including digital signatures, encryption, etc.

  3. XML Security Overview • Any “part” of an XML document can be signed with a digital signature • Any “part” can be encrypted • All the information that a recipient (or third party) needs is encoded in XML

  4. XML: Extra Massive Luggage • A set of inter-related documents • XML Documents • Data types: DTD’s and Schema • Xpath, a language for XML trees • Xpointers, for referencing XML parts • Transformations: XSLT and XSL; CSS • and XML security schema

  5. XML and Security in the News(Infoworld, Oct. 14) Addressing corporate security concerns, Kontiki this week announced the integration of its DMS with VeriSign's new Access Management System for user authentication, authorization, and management. Achieved through an XML network connector coupled with Web services standards including SOAP, the integration provides encryption for digital video and documents after they arrive on a PC desktop.

  6. Academics Notice XML • Journal of the ACM (a small computer professionals society) • May 20002 • “On XML Integrity Constraints in the Presence of DTDs” • W. Fan and L. Libkin • Factoid: there are DTD’s for which there is no finite XML document instance

  7. Understanding XML Mechanisms • Three interrelated topics: • XML representation • Representing signatures, keys, the crypto methods, etc. • XML document structure • and … • What XML security accomplishes • We’ll proceed in reverse order

  8. Encryption, the Confidentiality Mechanism • Key encrypts data, produces random-looking data - ciphertext • Unique key decrypts ciphertext, produces data This is data which must be kept from prying eyes 7aY28afWeoH7YHJ87 98UJJH3TYGjhhgu6 76ytGby6tLfT56red1er Algorithm and key Inverse algorithm and key

  9. Authentication, Signatures • Data may not be secret, but the sender is very important This is data which is important only if it comes from someone who is important Signature of I.M. Important is 9sad082fcBEs3re0dHf This is data which is important only if it comes from someone who is important Algorithm and public key

  10. Usage Example Description of services, amount due, data Signed by J. Contractor Payment authorization Check signed by CFO signed by J. Contractor Bank Account No Pay to J. Contractor Amount Signed by Treasurer

  11. Related Standards • S/MIME. Secure message formats • Very similar to XML security, but not extensible, less flexible • SSL, TLS protocols • These don’t have digital signatures • Data protection is only during transit • XML documents can be stored, processed later

  12. Signatures and Hashes • A document can be very long • Public key algorithms take a long time to encrypt one “block” of data • 1K bits, about 1 millisecond • Reduce document to a single block using a one-way hash function • Sign the hash • It’s easy to verify that “binary string” = Hash(doc)

  13. What Does an XML Sig Sign? • A Signature Value is the result of applying the Signature Method to the SignedInfo data item • The SignedInfo contains one or more References • A Reference tells you how to find the stuff to sign and what its DigestValue is • If the DigestValue doesn’t match the data, the signature doesn’t mean anything!

  14. XML Security Syntax • http://www.w3.org/TR/2002/REC-xmldsig-core-20020212/xmldsig-core-schema.xsd • Namespace www.w3.org/2001/09/xmldsig# • Signature contains this stuff: • Signed Info • Canonicalization Method, Signature Method, References • Signature Value (base64binary) • Key Info (optional) • Name, value, retrieval method, X509Data, etc. • Object (optional) • ID, Mime type, Data

  15. XML Document Reference Reference Object Signed Data Sign Anything, Here or There XML Document XML Signature Signed Info Reference

  16. Canonicalize Select a node set Digest (Hash) Sig Value Create XML SignedInfo base64binary Sign Processing Flow For a Reference XML Document Integer Value

  17. A Reference <Reference URI=…> URI can be to the whole document, a pointer to an ID, a URL, or omitted! <transforms> <transform Algorithm=base64> <DigestMethod Algorithm=MD5> <DigestValue> H7s2L9FF3x71mO87ZaIw3 </DigestValue>

  18. Selecting Parts, XPath • NB, it’s optional • A regular expression language for trees • Lets you select a set of node by reference and refer to them as a single object • Ancestor relations • Predicates • String matching (all nodes with ID beginning with “mydigitalsignature”)

  19. The Manifest (optional feature) • Like a table of contents for SignedInfo • There are no Objects, only References • References include digests (one-way hashes) • By signing the manifest you sign the digests of the References • If the digests don’t match the data, application can decide to selectively reject items

  20. Namespaces • A namespace disambiguiates label names • “telephone_number” might be in many schema • somenamespace:telephone_number helps with parsing • namespace declarations in XML docs establish nested scopes • should a signature include all the namespace scopes above it?

  21. Canonicalization:A Pitfall for XML • Serialize and Encode the Data • It’s why MIME uses BASE64 • protects the data from other protocols • removes ambiguities about end of line, tab, etc. • XML has two special case complications • namespaces, to include or not to include? • Schema can change lexigraphic properties • String termination, tag delimiters • Must have full parse tree and node delimiters!

  22. Key Management:A Man’s Reach Must Exceed His Grasp • Slow road to standardization, XKMS • Key retrieval, key information, signature validation, key registration • XML encoding, query/response protocol uses SOAP • X-KISS, the information service • hides X.509v3 complexity, bridges directory services, handles revocation, understands trust chains • X-KRSS, the key registration service • for storing new keys and their information

  23. Other Topics • ETSI, Advanced XML Signatures • Encryption and Algorithm Details • Access Control, P3P Privacy, Digital Rights Management • Applications (e.g., SOAP) • SDK’s • RSA, Inc. (?), Dot-Net • Books • XML Security (RSA), Secure XML (Eastlake & Niles), Advanced SOAP for Web Development (Livingston)

  24. Conclusion • XML, a rich set of tools • (Maybe too rich) • Security for XML documents can be defined using XML • Can protect documents in transit or in storage • Reusable • On to SOAP, an XML application

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