EIE424 Distributed Systems and Networking Programming –Part II

1. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Services Security 6. Web Services Security

2. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security References • U.Wahli, G.G. Ochoa, S. Cocasse and M. Muetschard, WebSphere Version 5.1 Web Services Handbook, IBM Redbooks, 2nd Ed, 2004 • M. Colan and J. Miller, “Understanding Web Services Security”, http://ibm.com/developerworks/speakers/colan

3. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security • Web services security is one of the most important Web services issues • Consider the following simple Web services-based application: Bank Data Center Bank Teller 1 Network Bank Teller 2

4. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security • If no security measure has been applied, the three major risk factors are: • Unauthorized transactions (Authorization) Teller 2 in fact is an imposer sending a SOAP message to the data center to request money withdrawal • Readable messages in clear text (Confidentiality) The account number and balance in the SOAP packet is read by the imposer on the network and he later uses them to withdraw money from that account • SOAP message susceptible to modification (Integrity) The SOAP message is intercepted and modified by the imposer. Money is deposited to another account

5. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security • With the advance of Internet technology, various security measures have been imposed to protect Web communications • The most popular one is HTTPS/SSL which provides “protocol-level” or “transport-level” security • Facilitate identification, basic authentication, encryption, and built-in integrity check • Provide point-to-point security across one connection • The above security risks can be removed by using HTTPS/SSL

6. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security • Consider a more complicate Web services-based application: Backend Application Web server protected by HTTPS Business Partner 1 secure Web Services Gateway protected by HTTPS Internet secure secure secure??? Business Partner 2 Web server protected by HTTPS Backend Application

7. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security • Even if HTTPS has been used in all Internet connections, the above application still has security and other problems • HTTPS provides point-to-point security only. Hence the security after the Web server is not guaranteed (need end-to-end security) • Business Partner 1 can deny the messages it sent to Business Partner 2 since there is no proof about the originator of the messages (need non-repudiation) • There is no record of all transactions so there is no way to look for security problems after the fact (need auditing) • Since all incoming and outgoing messages need to encrypt, demand much CPU time from all servers

8. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security • A message level security measure is required to provide not only point-to-point security but end-to-end security • Can be achieved by embedding security information in the SOAP message itself credentials SOAP message Secure secure Web Services Gateway protected by HTTPS Internet secure secure Secure

9. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security • To ensure interoperability, a standard to define new security elements in SOAP messages is needed • WS-Security specification covers a standard set of SOAP extensions that can be used when building secure Web services • It defines how to use and build upon existing security technologies (e.g. PKI, Kerberos, SSL, XML encryption, XML Digital Signature, etc.) for Web services • WS-Security specification was formalized in April 2002 • More specifications have been added and consolidated by the OASIS consortium, a non-profit organization that drives the development of e-business standards • WS-Securityv1.0 is an OASIS standard as of April 2004 which covers mainly the extension of SOAP messages

10. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security A Brief Review of Core Security Technologies • Common core technologies that are being used for security purpose include • Symmetric encryption • Asymmetric encryption • Hash function and digital signature • XML encryption • XML digital signature

11. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security Symmetric Encryption • Encryption – convert the data concerned into another form based on a key. Without the key, the data cannot be converted back to the original form • Symmetric – the same algorithm and key are used for both encryption and decryption (except for a slight rearrangement of the key) • Advantage – fast (compare with asymmetric algorithms) • Drawback – both encryption and decryption keys must remain secret • Interesting problem – how do you send your key to your partner securely? • Common symmetric encryption algorithms, DES, AES …

12. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security Plain text message Plain text message Sender Receiver Cipher text message The same key is used for both encryption and decryption Secret Key generator

13. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security Asymmetric Encryption • Asymmetric Encryption – different keys will be used for encryption and decryption • Usually one key is made known to public, the other key is kept secret • Advantage – solve the problem of distributing the key • Drawback – slower than symmetric algorithm • The most common asymmetric encryption algorithm, RSA, which is named after the three inventors, R. Rivest, A. Shamir and L. Adleman • Its security is based on the intractability of the factorization of large integers – what are the two factors of the number 8876044532898802067?

14. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security Plain text message Plain text message Sender Receiver Cipher text message Asymmetric key pair generator Different keys are used for encryption and decryption

15. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security • Two common ways of using asymmetric encryption • Sender: public key. Receiver: private key To ensure the encrypted message (using the public key) can only be seen by a particular receiver (decrypted using the private key) • Sender: private key. Sender: public key If a recipient successfully decrypts a message encrypted with our public key, they know this message is sent by me Hence can be used for identifying the originator of the message

16. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security Plain text message Plain text message A hybrid approach – Digital Envelope Sender Receiver Cipher text message Digital Envelope Private key Symmetric key generator Asymmetric key pair generator Public key

17. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security • Advantages: • Fast, since asymmetric encryption is applied only to a key, which is usually not so long in length • Secure, since we don’t need to send the symmetric key thru the network to the sender or receiver • SSL is an example that uses the above hybrid approach • Most of the security issues are solved with protocols based on combinations of symmetric encryption, asymmetric encryption, and hash functions

18. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security Hash Functions and Digital Signature • To ensure dataintegrity, an identifier needs to be sent with sender’s data to proof that the data have not been changed during transmission • To achieve non-repudiation, the identifier should further proof the source who generates the identifier • Based on the digital signature technique, a hash, or “digest" of the transmitted data is extracted and encrypted by a private key • The receiver extracts the encrypted digest and decrypted by a public key • The receiver uses the same algorithm to generate the digest of the data object & compare with the encrypted one • If they match, the data object is from the right source

19. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security Data Object Data Object Digital signature Encrypted Digest Digest Send to the receiver Hashing Algorithm Private key of transmit entity • Two important properties of the digest: • Given an input stream and its hash code, it is practically impossible to find a second stream with the same hash code • A small change to the original input stream produces a huge change in the hash code

20. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security Hashing Algorithm Data Object If the digests match, the data object is from the right source Receive from the sender Public key of transmit entity

21. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security • Data integrity is ensured because if an attacker modifies the data object, the digests will not match • If an attacker tries to modify the data object as well as the digest, he will still fail because the attacker does not know the private key • Non-repudiation is achieved because if the receiver can decrypt the digest, the digest must be sent from the right source • In the above case, the data object is not encrypted. Anybody can read it • If the data object itself is considered as confidential, data encipherment can be applied to further encrypt the data object

22. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security XML Encryption • The XML Encryption standard defines ways to encrypt all or part of an XML document • Encrypted info is replaced with a single <EncryptedData> element • Allow encrypting different parts of the same document with different keys • Allow encrypting the whole document, a single element, or just the text of an element

23. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security Inside <EncryptedData> • An <EncryptedData> element contains the following elements • <EncryptionMethods> The algorithm used to encrypted the data • <KeyInfo> Information about the key used to encrypt the data • <CipherData> Contain the actual encrypted data • W3C XML Encryption specifications were proposed by IBM, Microsoft and Entrust • Currently it is still a W3C recommendation. Details can be found in http://www.w3.org/Encryption

24. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security XML Digital Signature • The XML Digital Signature standard defines rules for creating a digital signature and storing that signature inside an XML document • The <Signature> element has 3 main parts • <SignedInfo> Information about what is signed (such as the algorithm used to generate the digest and the encryption algorithm) • <SignatureValue> The value of the digital signature itself • <KeyInfo> The public key used to verify the signature (optional) • Now a W3C recommendation (http://www.w3.org/Signature)

25. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security Basic Syntax of WS-Security • <wsse:Security> is the “container” for security-related info • Place in the header means apply to the whole SOAP msg <S: Envelope xmlns:S=“http://schemas.xmlsoap.org/soap/envelope/”> <S:Header> <wsse:Security xmlns:wsse="http://schemas.xmlsoap.org/ws/2003/06/secext”> <wsse:UsernameToken> ... </wsse:UsernameToken> <EncryptedKey xmlns="http://www.w3.org/2001/04/enc-enc-enc#"> ... </EncryptedKey> <Signature xmlns:"http://www.w3.org/2000/09/xmldsig#"> ... </Signature> </S:Header> Define and use WS-Security namespace Authentication Confidentiality, adopt XML Encryption Integrity, adopt XML Digital Signature

26. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security Encrypted contents inside the Body can be included in the <EncryptedData> element <S:Body> ... <EncryptedData> ... </EncryptedData> </S:Body> </S:Envelope>

27. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security WS-Security for Authentication – Security Token • WS-Security defines security tokens, which can contain various requestors’ claims (a declaration made by some entity) • e.g. a username and optional password, an X.506 certificate, or a Kerberos ticket • Basically there are two types of tokens: • UsernameToken and BinarySecurityToken • UsernameToken is the simplest one. Contain a mandatory username and optional password • BinarySecurityToken however contains encoded binary data that is suitable for storing X.509 certificate or Kerberos ticket

28. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security <S: Envelope xmlns:S=“http://schemas.xmlsoap.org/soap/envelope/”> <S:Header> <wsse:Security xmlns:wsse="http://schemas.xmlsoap.org/ws/2003/06/secext” soapenv:mustUnderstand=“1”> <wsse:UsernameToken wsu:ID=“myToken”> <wsse:Username>danielLun</wsse:Username> <wsse:Password>passw0rd</wsse:Password> </wsse:UsernameToken> </wsse:Security> </S:Header> <S:Body> ... </S:Body> </S:Envelope> The other part of the message can refer to this UsernameToken with this ID Requester provides the claim (username and password) to the server for validation. Server must understand this header or an error should be returned • Sending username and password in this way is obviously not secure. • Need to be used with WS-Security encryption to hide away both username and password

29. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security <S: Envelope xmlns:S=“http://schemas.xmlsoap.org/soap/envelope/”> <S:Header> <wsse:Security xmlns:wsse="http://schemas.xmlsoap.org/ws/2003/06/secext” soapenv:mustUnderstand=“1”> <wsse:BinarySecurityToken wsu:ID=“myToken” ValueType=“wsse:Kerberosv5ST” EncodingType=“wsse:Base64Binary> XIFNWZz99UUbalqIEmJZc0 ... </wsse:BinarySecurityToken> </wsse:Security> </S:Header> <S:Body> ... </S:Body> </S:Envelope> Using Kerberos service ticket Specify that the binary data of Kerberos service ticket will be encoded using Base64 representation Kerberos ticket or x.509 certificate are also referred as signed security tokens since the data has been cryptographically signed by a specific authority • Since any third party can take the ticket or certificate and include in their application, the ticket or certificate alone cannot serve as proof of possession

30. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security WS-Security for Confidentiality – Using XML Encryption • For WS-Security, there is no intention to create new methods but integrating the existing technologies to achieve security, e.g. XML Encryption • <EncryptedKey> element is placed in security header for implementing digital envelope • <EncryptionMethod> Algorithm for the encryption of the symmetric key • <KeyInfo> Identifier of a public key used for encryption, assume both the client and server understand the meaning of the identifier • <CipherData><CipherValue> Encrypted symmetric key value • <ReferenceList> List of <DataReference> to contents encrypted with this symmetric key

31. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security Plain text message Plain text message Sender Receiver Cipher text message Digital Envelope Private key Symmetric key generator Asymmetric key pair generator Public key

32. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security <S: Envelope xmlns:S=“http://schemas.xmlsoap.org/soap/envelope/”> <S:Header> <wsse:Security ...> <EncryptedKey xmlns=“http://www.w3.org/2001/04/xmlenc#”> <EncryptionMethod Algorithm = “http://www.w3.org/2001/04/xmlenc#rsa-1_5”> </EncryptionMethod> <KeyInfo xmlns=“http://www.w3.org/2000/09/xmlsig#”> <wsse:SecurityTokenReference> <wsse:KeyIdentifier>u3AA1M+DMOA1bX/vWJ ... </wsse:KeyIdentifier> </wsse:SecurityTokenReference> </KeyInfo> <CipherData> <CipherValue>cdck0cWh94oF5xBoEm ... </CipherValue> </CipherData> <ReferenceList> <DataReference URI = “#myToken”> </DataReference> </ReferenceList> </EncryptedKey> Symmetric key is encrypted with RSA-1.5 algorithm using the public key as stated below The key identifier (not the key itself) of a public key The encrypted symmetric key The URI should be referred to when the symmetric key is used by other part of message

33. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security <S:Body> <po xmlns: ...> <wsse:Security ...> <EncryptedData xmlns=“http://www.w3.org/2001/04/xmlenc#” Id=“myToken” Type=“http://www.w3.org/2001/04/xmlenc#Content”> <EncryptionMethod Algorithm = “http://www.w3.org/2001/04/xmlenc#tripledes-cbc”> </EncryptionMethod> <CipherData> <CipherValue>Ew7Zggr8z3 ... </CipherValue> </CipherData> </EncryptedData> <shipTo> <company>The Skateboard Warehouse</company> <street>One Warehouse Park</street> <postalCode>01775</postCode> </shipTo> : </po> </S:Body> Using the symmetric key as mentioned in the header for encrypting this part The encryption algorithm is triple-DES, a symmetric encryption algorithm The original data is the credit card info of the customer, but now is replaced by a ciphered code The less sensitive part is sent to the server without encryption

34. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security WS-Security for Integrity and Non-repudiation – Using XML Digital Signature Data Object Data Object Digital signature Encrypted Digest Digest Send to the receiver Hashing Algorithm Private key of transmit entity

35. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security <S: Envelope xmlns:S=“http://schemas.xmlsoap.org/soap/envelope/”> <S:Header> <wsse:Security ...> <wsse:BinarySecurityToken wsu:ID=“myToken” ValueType=“wsse:X509v3” : </wsse:BinarySecurityToken> <Signature xmlns=“http://www.w3.org/2000/09/xmldsig#”> ... XML Digital Signature of body_id is placed here ... ... It is encrypted with a private key of which its ... public key counterpart is indicated in myToken ... </Signature> </wsse:Security> </S:Header> <S:Body xmlns:wsu= ... wsu:ID=“body_id”> ... </S:Body> </S:Envelope> Namespace for XML Digital Signature which defines the element <Signature> • The X.509 certificate contains the public key of the client • Its private counterpart will be used to encrypt the digest for generating the signature • The certificate will be sent to server

36. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security <Signature xmlns=“http://www.w3.org/2000/09/xmldsig#”> <SignedInfo> ... Indicate what is to be signed ... ... A digest of body_id is generated and placed here... ... Define the algorithms used to generate the digest.. : </SignedInfo> <SignatureValue> : ... The actual signature ... ... The digest of <SignedInfo> part will be generated ... and encrypted using the private key as implied ... in <KeyInfo> ... : </SignatureValue> <KeyInfo> : ... Indicate the security token, i.e. myToken in this case, ... which keeps a public key. Its private key counterpart ... will be used for encrypting the digest of <SignedInfo> : </KeyInfo> </Signature>

37. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security <KeyInfo> <wsse:SecurityTokenReference> <wsse:Reference URI=“#myToken”></wsse:Reference> </wsse:SecurityTokenReference> </KeyInfo> • A security token is referring to in <KeyInfo> • The URI “myToken” indicates that the X.509 certificate defined at the beginning of SOAP message will be used • X.509 certificate contains much information about its owner, one of them is the public key • Its private key counterpart will be used to encrypt the digest

38. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security • The target is signed rather indirectly in order to ensure both the target and the <SignedInfo> subtree will not be altered unnoticeably by the imposer • A digest of the target (i.e. the Body in this case) is generated and put into the <SignedInfo> subtree • The encrypted digest of the whole <SignedInfo> subtree is then generated and put into <SignatureValue> <S: Envelope ... > <S:Header> <wsse:Security ...> : <Signature ... > <SignedInfo> : </SignedInfo> <SignatureValue> : </SignatureValue> </Signature> </wsse:Security> </S:Header> <S:Body...> : </S:Body> </S:Envelope> Encrypted Digest Digest

39. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security • Imposer cannot change the target (i.e. Body) unnoticeably since it will not match with the digest in <SignedInfo> • Imposer cannot change the body and the digest in <SignedInfo> together unnoticeably , since it will not match with the digest in <SignatureValue> • Imposer cannot change digest in <SignatureValue> since he does not have the private key <S: Envelope ... > <S:Header> <wsse:Security ...> : <Signature ... > <SignedInfo> : </SignedInfo> <SignatureValue> : </SignatureValue> </Signature> </wsse:Security> </S:Header> <S:Body...> : </S:Body> </S:Envelope> Encrypted Digest Digest

40. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security <SignedInfo> <CanonicalizationMethod Algorithm = “http://www.w3.org/2001/10/xml-exc-c14n#”/> <SignatureMethod Algorithm = “http://www.w3.org/2000/09/xmlsig#rsa-sha1”/> <Reference URI=“#body_id”> <Transforms> <Transform Algorithm = “http://w3.org/2001/10/xml-exc-c14n#”/> </Transforms> <DigestMethod Algorithm = “http://www.w3.org/2000/09/xmldsig#sha1”/> <DigestValue>Ojjw8nkT3jJoNN/Axsd ...</DigestValue> </Reference> </SignedInfo> • The <Body> is first transformed using the algorithm EXC-C14N into a canonicalform • The digest of it is generated using an algorithm SHA1 • The digest is stored in <DigestValue> element

41. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security Canonical form XML document • Two XML documents can be physically different but logically equivalent. E.g. by canonicalization, both <?xml version=“1.0” encoding=“us-ascii”?> <foo b=“b” a=“a” ></foo> and <?xml version=“1.0” encoding=“us-ascii”?> <foo a=“a” b=“b”/> will be converted into <?xml version=“1.0” encoding=“us-ascii”?> <foo a=“a” b=“b”></foo> Converting the <SignedInfo> to canonical form before generating its digest can avoid signature mismatch arisen from legitimate alternation of XML header by intermediate servers

42. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security <SignedInfo> <CanonicalizationMethod Algorithm = “http://www.w3.org/2001/10/xml-exc-c14n#”/> <SignatureMethod Algorithm = “http://www.w3.org/2000/09/xmlsig#rsa-sha1”/> <Reference URI=“#body_id”> : </Reference> </SignedInfo> • Before generating the digest of <SignedInfo>, it should first be converted into a canonical form using EXC-C14N canonicalization algorithm • The digest of <SignedInfo> is generated using the SHA1 algorithm and encrypted using RSA asymmetric encryption algorithm (hence RSA-SHA1)

43. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security Verification of the Digital Signature When the server receives the signed SOAP message, it should • generate the digest of the target (i.e. Body in this case) using the indicated algorithms (EXC-C14N and SHA1) • Compare with the one in <SignedInfo> • If match, decrypt the signature using the public key given in the security token • Extract the <SignedInfo> subtree of the SOAP message • Generate the digest of <SignedInfo> using the algorithms indicated (EXC-C14N and SHA1) • Compare the generated digest and the one in <SignatureValue>

44. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security WS-Security Implementation in WebSphere Handler Handler Request Request Provider App Requester App Response Response Deployment Descriptor Deployment Descriptor Client WebSphere App Server • The security functions required in the handlers are defined in the respective Deployment Descriptor • No need to add or change any code in the Java source • Allow a security manager to control and change all security options without interfering with developer tasks

45. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security • WebSphere Studio makes it easy to add WS-Security to a Web service • Security Handler module can be added to contains the code for Web Service Security functions • Client’s Request Unit: SOAP request header construction Security token generation, digital signature generation or content encryption • Server’s Request Unit: SOAP request header processing Validate security tokens, set up security content, decrypt content or digital signature validation • Server’s Response Unit: SOAP response header construction Digital signature generation, content encryption • Client’s Response Unit: SOAP response header processing Decrypt content and digital signature validation

46. EIE424 Distributed Systems and Networking Programming –Part II 6. Web Service Security The Roadmap of WS-Security SOAP Foundation Layer WS-Security Layer WS-SecureConversation WS-Federation WS-Authentication WS-Policy WS-Trust WS-Privacy Current Standards Specifications in progress