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XML encryption

XML encryption is a specification developed by World Wide Web (WWW) Consortium (W3C) in 2002 containing the steps to encrypt data, the steps to decrypt encrypted data, the syntax to represent XML encrypted data, the information used to decrypt the data, and a list of encryption algorithms such as triple Data Encryption Standard (DES), Advanced Encryption Standard (AES), and Rivest-Shamir-Adleman algorithm (RSA).

There is an important distinction between v5.x and v6 and later applications. The information in this article supports v5.x applications only used with WebSphere Application Server v6.0.x and later. The information does not apply to v6 and later applications.

We can apply XML encryption to an XML element, XML element content, and arbitrary data, including an XML document. For example, suppose needed to encrypt the <CreditCard> element shown in the example 1.

Example 1: Sample XML document

Example 2: XML document with a common secret key:

Example 2 shows the XML document after encryption. The <EncryptedData> element represents the encrypted <CreditCard> element. The <EncryptionMethod> element describes the applied encryption algorithm, which is triple DES in this example. The <KeyInfo> element contains the information to retrieve a decryption key, which is a <KeyName> element in this example. The <CipherValue> element contains the ciphertext obtained by serializing and encrypting the <CreditCard> element. 

<PaymentInfo xmlns='http://example.org/paymentv2'>   <Name>John Smith</Name>   <EncryptedData Type='http://www.w3.org/2001/04/xmlenc#Element'
     xmlns='http://www.w3.org/2001/04/xmlenc#'>     <EncryptionMethod
       Algorithm='http://www.w3.org/2001/04/xmlenc#tripledes-cbc'/>        <KeyInfo xmlns='http://www.w3.org/2000/09/xmldsig#'>          <KeyName>John Smith</KeyName>        </KeyInfo>        <CipherData>          <CipherValue>ydUNqHkMrD...</CipherValue>        </CipherData>   </EncryptedData> </PaymentInfo>

Example 3: XML document encrypted with the public key of the recipient:

In example 2, it is assumed that both the sender and recipient have a common secret key. If the recipient has a public and private key pair, which is most likely the case, the <CreditCard> element can be encrypted as shown in example 3. The <EncryptedData> element is the same as the <EncryptedData> element found in Example 2. However, the <KeyInfo> element contains an EncryptedKey. 

<PaymentInfo xmlns='http://example.org/paymentv2'>   <Name>John Smith</Name>   <EncryptedData Type='http://www.w3.org/2001/04/xmlenc#Element'
    xmlns='http://www.w3.org/2001/04/xmlenc#'>     <EncryptionMethod
      Algorithm='http://www.w3.org/2001/04/xmlenc#tripledes-cbc'/>     <KeyInfo xmlns='http://www.w3.org/2000/09/xmldsig#'>       <EncryptedKey xmlns='http://www.w3.org/2001/04/xmlenc#'>         <EncryptionMethod 
          Algorithm='http://www.w3.org/2001/04/xmlenc#rsa-1_5'/>         <KeyInfo xmlns='http://www.w3.org/2000/09/xmldsig#'>           <KeyName>Sally Doe</KeyName>         </KeyInfo>         <CipherData>           <CipherValue>yMTEyOTA1M...</CipherValue>         </CipherData>       </EncryptedKey>     </KeyInfo>     <CipherData>       <CipherValue>ydUNqHkMrD...</CipherValue>     </CipherData>   </EncryptedData> </PaymentInfo>

XML Encryption in the WSS-Core:

WSS-Core specification is under development by Organization for the OASIS. The specification describes enhancements to SOAP messaging to provide quality of protection through message integrity, message confidentiality, and single message authentication. The message confidentiality is realized by encryption based on XML Encryption.

The WSS-Core specification supports encryption of any combination of body blocks, header blocks, their sub-structures, and attachments of a SOAP message. The specification also requires that when we encrypt parts of a SOAP message, you prepend a reference from the security header block to the encrypted parts of the message. The reference can be a clue for a recipient to identify which encrypted parts of the message to decrypt.

The XML syntax of the reference varies according to what information is encrypted and how it is encrypted. For example, suppose the <CreditCard> element in example 4 is encrypted with either a common secret key or the public key of the recipient.

Example 4: Sample SOAP message: 

<SOAP-ENV:Envelope
  SOAP-ENV:encodingStyle='http://schemas.xmlsoap.org/soap/encoding/'
  xmlns:SOAP-ENV='http://schemas.xmlsoap.org/soap/envelope/'>   <SOAP-ENV:Body>     <PaymentInfo xmlns='http://example.org/paymentv2'>       <Name>John Smith</Name>       <CreditCard Limit='5,000' Currency='USD'>         <Number>4019 2445 0277 5567</Number>         <Issuer>Example Bank</Issuer>         <Expiration>04/02</Expiration>       </CreditCard>     </PaymentInfo>   </SOAP-ENV:Body> </SOAP-ENV:Envelope>

The resulting SOAP messages are shown in Examples 5 and 6. In these example, the <ReferenceList> and <EncryptedKey> elements are used as references, respectively.

Example 5: SOAP message encrypted with a common secret key: 

<SOAP-ENV:Envelope
  SOAP-ENV:encodingStyle='http://schemas.xmlsoap.org/soap/encoding/'
  xmlns:SOAP-ENV='http://schemas.xmlsoap.org/soap/envelope/'>   <SOAP-ENV:Header>     <Security SOAP-ENV:mustUnderstand='1'
      xmlns='http://schemas.xmlsoap.org/ws/2003/06/secext'>       <ReferenceList xmlns='http://www.w3.org/2001/04/xmlenc#'>         <DataReference URI='#ed1'/>       </ReferenceList>     </Security>   </SOAP-ENV:Header>   <SOAP-ENV:Body>     <PaymentInfo xmlns='http://example.org/paymentv2'>       <Name>John Smith</Name>       <EncryptedData Id='ed1'
        Type='http://www.w3.org/2001/04/xmlenc#Element'
        xmlns='http://www.w3.org/2001/04/xmlenc#'>         <EncryptionMethod
          Algorithm='http://www.w3.org/2001/04/xmlenc#tripledes-cbc'/>         <KeyInfo xmlns='http://www.w3.org/2000/09/xmldsig#'>           <KeyName>John Smith</KeyName>         </KeyInfo>         <CipherData>           <CipherValue>ydUNqHkMrD...</CipherValue>         </CipherData>       </EncryptedData>     </PaymentInfo>   </SOAP-ENV:Body> </SOAP-ENV:Envelope>

Example 6: SOAP message encrypted with the public key of the recipient: 

<SOAP-ENV:Envelope
  SOAP-ENV:encodingStyle='http://schemas.xmlsoap.org/soap/encoding/'
  xmlns:SOAP-ENV='http://schemas.xmlsoap.org/soap/envelope/'>   <SOAP-ENV:Header>     <Security SOAP-ENV:mustUnderstand='1'
      xmlns='http://schemas.xmlsoap.org/ws/2003/06/secext'>       <EncryptedKey xmlns='http://www.w3.org/2001/04/xmlenc#'>         <EncryptionMethod 
          Algorithm='http://www.w3.org/2001/04/xmlenc#rsa-1_5'/>         <KeyInfo xmlns='http://www.w3.org/2000/09/xmldsig#'>           <KeyName>Sally Doe</KeyName>         </KeyInfo>         <CipherData>           <CipherValue>yMTEyOTA1M...</CipherValue>         </CipherData>         <ReferenceList>           <DataReference URI='#ed1'/>         </ReferenceList>       </EncryptedKey>     </Security>   </SOAP-ENV:Header>   <SOAP-ENV:Body>     <PaymentInfo xmlns='http://example.org/paymentv2'>       <Name>John Smith</Name>       <EncryptedData Id='ed1'
        Type='http://www.w3.org/2001/04/xmlenc#Element'
        xmlns='http://www.w3.org/2001/04/xmlenc#'>         <EncryptionMethod
          Algorithm='http://www.w3.org/2001/04/xmlenc#tripledes-cbc'/>         <CipherData>           <CipherValue>ydUNqHkMrD...</CipherValue>         </CipherData>       </EncryptedData>     </PaymentInfo>   </SOAP-ENV:Body> </SOAP-ENV:Envelope>

Relationship to digital signature:

The WSS-Core specification also provides message integrity, which is realized by a digital signature based on the XML-Signature specification.

A combination of encryption and digital signature over common data introduces cryptographic vulnerabilities.


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Secure web services for v5.x applications using XML encryption


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