How to Use XML Security Standards in Real World Aleksey Sanin <[e-mail]> O

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How to Use XML Security Standards in Real World
Aleksey Sanin ltaleksey_at_aleksey.Comgt OReilly
Open Source ConventionJuly 7 - 11, 2003
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Agenda

• W3C XML Security specifications
• XML Security Library
• Practical XML Security

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W3C XML Security Standards

• XML Canonicalization and Exclusive XML
  Canonicalization (W3C recommendations)http//www.
  w3.org/TR/xml-c14n/http//www.w3.org/TR/xml-exc-c
  14n/
• XML Signature (W3C recommendation)http//www.w3.o
  rg/TR/xmldsig-core/
• XML Encryption (W3C recommendation)http//www.w3.
  org/TR/xmlenc-core/
• XML Key Management (W3C working
  draft)http//www.w3.org/TR/xkms2/

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Why Do We Need New Specifications?

• SSL/TLS provides transport level security when
  Web services need messages level security
• Store message for later use
• Session keys in SSL/TLS
• Fine grained security for XML documents

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XML Canonicalization

• ltTest a"aa" b"bb"/gt
• ltTest b"bb" a"aa"gtlt/Testgt
• ltTest a"aa" b"bb"gtlt/Testgt

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XML Canonicalization (Continue)

• C14N is a serialization of XML document or XPath
  node set to a binary string.
• There are many C14N algorithms (W3C C14N,
  Exclusive C14N).
• Same input data (XML document or XPath node set)
  and same C14N algorithm produce the same binary
  string.
• Use Exclusive C14N.

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XML Digital Signature Structure

• ltdsigSignature ID?gt
• ltdsigSignedInfogt
• ltdsigCanonicalizationMethod Algorithm /gt
• ltdsigSignatureMethod Algorithm /gt
• ltdsigReference URI? gt
• lt/dsigSignedInfogt
• ltdsigSignatureValuegt
• ltdsigKeyInfogt?
• (ltdsigObject ID?gt)
• lt/dsigSignaturegt

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XML Digital Signature Structure Reference element

• ltdsigReference URI? gt
• (ltdsigTransformsgt
• (ltdsigTransform Algorithm /gt)
• lt/dsigTransformsgt)?
• ltdsigDigestMethod Algorithm gt
• ltdsigDigestValuegt
• lt/dsigReferencegt

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XML Digital Signature Structure KeyInfo element

• ltdsigKeyInfogt
• ltdsigKeyNamegt?
• ltdsigKeyValuegt?
• ltdsigRetrievalMethodgt?
• ltdsigX509Datagt?
• ltdsigPGPDatagt?
• ltencEncryptedKeygt?
• ltencAgreementMethodgt?
• ltdsigKeyNamegt?
• ltdsigRetrievalMethodgt?
• ltgt?
• lt/dsigKeyInfogt

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XML Digital Signature Generation

• Calculate digests other signed data from
  ltdsigReference/gt element.
• Compose ltdsigSignedInfo/gt element.
• Calculate signature other ltdsigSignedInfo/gt
  element and place result in ltdsigSignatureValue/gt
  element.

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XML Digital Signature Enveloped Signature Example

• lt?xml version"1.0" encoding"UTF-8"?gt
• ltEnvelopegt
• ltSignedDatagtHello, World!lt/SignedDatagt
• ltSignature xmlns"http//www.w3.org/2000/09/xmld
  sig"gt
• ltSignedInfogt
• ltCanonicalizationMethod Algorithm"http//ww
  w.w3.org/"/gt
• ltSignatureMethod Algorithm"http//www.w3.or
  g/2000/09/xmldsigrsa-sha1"/gt
• ltReference URI""gt
• ltTransformsgt
• ltTransform Algorithm"http//www.w3.org/
  2000/09/xmldsigenveloped-signature"/gt
• lt/Transformsgt
• ltDigestMethod Algorithm"http//www.w3.org
  /2000/09/xmldsigsha1"/gt
• ltDigestValuegt9H/rQr...lt/DigestValuegt
• lt/Referencegt
• lt/SignedInfogt
• ltSignatureValuegtMx4psI...lt/SignatureValuegt
• ltKeyInfogtltKeyNamegtMy-RSA-Keylt/KeyNamegtlt/KeyInf
  ogt
• lt/Signaturegt
• lt/Envelopegt

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XML Digital Signature Enveloped Signature
Example (Continue)

• Digested data
• ltEnvelopegt
• ltSignedDatagtHello, World!lt/SignedDatagt
• lt/Envelopegt
• Signed data
• ltSignedInfogt
• ltCanonicalizationMethod Algorithm"http//ww
  w.w3.org/"/gt
• ltSignatureMethod Algorithm"http//www.w3.or
  g/2000/09/xmldsigrsa-sha1"/gt
• ltReference URI""gt
• ltTransformsgt
• ltTransform Algorithm"http//www.w3.org/
  2000/09/xmldsigenveloped-signature"/gt
• lt/Transformsgt
• ltDigestMethod Algorithm"http//www.w3.org
  /2000/09/xmldsigsha1"/gt
• ltDigestValuegt9H/rQr...lt/DigestValuegt
• lt/Referencegt
• lt/SignedInfogt

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XML Encryption Structure

• ltencEncryptedData Id? Type? MimeType?gt
• ltencEncryptionMethod Algorithm /gt?
• ltdsigKeyInfogt?
• ltencCipherDatagt
• ltencCipherValuegt?
• ltencCipherReference URI?gt?
• lt/encCipherDatagt
• ltencEncryptionPropertiesgt?
• lt/encEncryptedDatagt

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XML Encryption Example

• lt?xml version"1.0" encoding"UTF-8"?gt
• ltEncryptedData xmlns"http//www.w3.org/2001/04/xm
  lenc" Type"http//www.w3.org/2001/04/xmlencElem
  ent"gt
• ltEncryptionMethod Algorithm"http//www.w3.org
  /2001/04/xmlenctripledes-cbc"/gt
• ltKeyInfo xmlns"http//www.w3.org/2000/09/xmld
  sig"gt ltKeyNamegtMy-DES-Keylt/KeyNamegt
• lt/KeyInfogt
• ltCipherDatagt
• ltCipherValuegtWXlDy...lt/CipherValuegt
• lt/CipherDatagt
• lt/EncryptedDatagt

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XML Security Toolkits

• XML Security Library (C/C)http//www.aleksey.co
  m/xmlsec
• Microsoft .NET (C)http//msdn.microsoft.com/netf
  ramework/
• DataPower (Hardware)http//www.datapower.com/prod
  ucts/xs40.html
• Apache XML Security (Java)http//xml.apache.org/s
  ecurity/index.html
• Baltimore Technologies (Java)http//www.baltimore
  .com/keytools/xml/
• IBM XML Security Suite (Java)http//www.alphawork
  s.ibm.com/tech/xmlsecuritysuite
• Phaos Technology Corporation (Java)http//phaos.c
  om/products/category/xml.html

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XML Security Library

• Open Source (MIT license)
• Based on LibXML2/LibXSLT and your favorite
  cryptographic library
• Strong standards support
• Very fast
• Can use practically any cryptographic library
  (OpenSSL, GnuTLS, NSS, )
• Portable (Linux, OpenBSD, FreeBSD, Solaris,
  Windows, Mac OS X, )

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XML Security Library Objects

• Transforms
• Keys
• Keys Manager
• Operation Contexts
• Signature
• Encryption
• Transforms
• Key selection
• Templates

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XML Security Library Templates

• lt?xml version"1.0" encoding"UTF-8"?gt
• ltEnvelopegt
• ltSignedDatagtHello, World!lt/SignedDatagt
• ltSignature xmlns"http//www.w3.org/2000/09/xmld
  sig"gt
• ltSignedInfogt
• ltCanonicalizationMethod Algorithm"http//ww
  w.w3.org/"/gt
• ltSignatureMethod Algorithm"http//www.w3.or
  g/2000/09/xmldsigrsa-sha1"/gt
• ltReference URI""gt
• ltTransformsgt
• ltTransform Algorithm"http//www.w3.org/
  2000/09/xmldsigenveloped-signature"/gt
  lt/Transformsgt
• ltDigestMethod Algorithm"http//www.w3.org
  /2000/09/xmldsigsha1"/gt
• ltDigestValuegtlt/DigestValuegt
• lt/Referencegt
• lt/SignedInfogt
• ltSignatureValuegtlt/SignatureValuegt
• ltKeyInfogt
• ltKeyNamegtlt/KeyNamegt
• lt/KeyInfogt
• lt/Signaturegt

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XML Security Library Signing or Encrypting XML
Document

• Prepare keys manager (the same keys manager can
  be shared by multiple operations)
• Create or load "template" and select the start
  node (ltdsigSignature/gt or ltencEncryptedData/gt)
• Create signature (xmlSecDSigCtx) or encryption
  (xmlSecEncCtx) context object
• Specify signature or encryption key in the
  template (by name, for example) or in the context
  object
• Sign or encrypt data and consume the result
• Destroy context object

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XML Security Library Signature Example

• int sign_template(xmlDocPtr tmpl, xmlNodePtr
  startNode,
• xmlSecKeyPtr key)
• xmlSecDSigCtxPtr dsigCtx
• / create signature context w/o keys manager /
• dsigCtx xmlSecDSigCtxCreate(NULL)
• if(dsigCtx NULL)
• fprintf(stderr,"Error failed to create
  context.\n")
• return(-1)
• / set signature key in the context /
• dsigCtx-gtsignKey xmlSecKeyDuplicate(key)
• if(dsigCtx-gtsignKey NULL)
• fprintf(stderr,"Error failed to duplicate
  key.\n")
• xmlSecDSigCtxDestroy(dsigCtx)
• return(-1)

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XML Security Library Signature Example (Continue)

• / sign the template /
• if(xmlSecDSigCtxSign(dsigCtx, startNode) lt 0)
• fprintf(stderr,"Error signature failed.\n")
  xmlSecDSigCtxDestroy(dsigCtx)
• return(-1)
• / destroy context object /
• xmlSecDSigCtxDestroy(dsigCtx)
• return(0)

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XML Security Library Verifying Signature

• Prepare keys manager (the same keys manager can
  be shared by multiple operations)
• Load signed document and select the start node
  (ltdsigSignature/gt or ltencEncryptedData/gt)
• Create signature (xmlSecDSigCtx) or encryption
  (xmlSecEncCtx) context object
• Verify signature or decrypt the data, consume the
  result
• Destroy context object

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XML Security Library Signature Verification
Example

• int verify_document(xmlDocPtr doc, xmlNodePtr
  startNode,
• xmlSecKeysMngrPtr keysMngr)
• xmlSecDSigCtxPtr dsigCtx
• int res
• / create signature context /
• dsigCtx xmlSecDSigCtxCreate(keysMngr)
• if(dsigCtx NULL)
• fprintf(stderr,"Error failed to create
  context.\n")
• return(-1)
• / Verify signature /
• if(xmlSecDSigCtxVerify(dsigCtx, startNode) lt 0)
  
• fprintf(stderr,"Error verification
  failed.\n")
• xmlSecDSigCtxDestroy(dsigCtx)
• return(-1)

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XML Security Library Signature Verification
Example (Continue)

• / check verification result /
• if(dsigCtx-gtstatus xmlSecDSigStatusSucceeded)
  
• / signature is valid /
• res 1
• else
• / signature is invalid /
• res 0
• / destroy signature context /
• xmlSecDSigCtxDestroy(dsigCtx)
• return(res)

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Practical XML Security

• Check what was actually signed
• Use pre-digested data
• Analyze used transforms
• Limit allowed digest, signature, encryption and
  transform algorithms
• Limit allowed key sources
• Check that data or key source matches expectation

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