Web Services Security: a preliminary study using Casper and FDR

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1 b Services Security: a preliminary study using Casper and FDR 01 Web Services Security: a preliminary study using Casper and FDR E. Kleiner and A.W. Roscoe

2 b Services Security: a preliminary study using Casper and FDR 02 Web Services - a quick overview Web Services is an XML-based architecture that was developed in order to make the coupling between distributed components looser. SOAP was defined by Microsoft and DevelopMentor to provide a way to envelop information using XML to exchange it between different computing systems. With the growth of the popularity and importance of the Web Services architecture, more and more standards have been defined for extending the functionality and for dealing with different concerns.

3 b Services Security: a preliminary study using Casper and FDR 03 Web Service - An example implementation

4 b Services Security: a preliminary study using Casper and FDR 04 SOAP request example!"###$%!& "# %! "#' ( "#' "#)&#"#)&# "# (* +"# ( "# %!!

5 b Services Security: a preliminary study using Casper and FDR 05 SOAP response example!"###$# "# %!& "#&%'%##(%!"#) "# %!&!

6 b Services Security: a preliminary study using Casper and FDR 06 Web Services Security - an overview Problems with securing web services with a secure transport layer (ex. SSL): SOAP is not bound to a specific transport layer. The message is protected only in a secure channel. The secure transport layer does not support intermediaries. Inefficiency. Web Services Security specification Was initially proposed by Microsoft in October Defines elements to incorporate security tokens within a SOAP message. XML-Signature and XML-Encryption are used for achieving integrity and confidentiality for the security tokens.

7 b Services Security: a preliminary study using Casper and FDR 07 Message M - taken from an Oasis proposed protocol <Envelope> <Header> <Security mustunderstand="1"> <BinarySecurityToken ValueType="x509v3" Id="myCert"> BV1 </BinarySecurityToken> <Signature> <SignedInfo> <CanonicalizationMethod Algorithm=... /> <SignatureMethod Algorithm=" <Reference URI="#body"> <Transforms> <Transform Algorithm=... /> </Transforms> <DigestMethod Algorithm=... /> <DigestValue> BV2 </DigestValue> </Reference> </SignedInfo> <SignatureValue> BV3 </SignatureValue> <KeyInfo> <SecurityTokenReference> <Reference URI="#myCert" /> </SecurityTokenReference> </KeyInfo> </Signature>

8 b Services Security: a preliminary study using Casper and FDR 08 <EncryptedKey> <EncryptedMethod Algorithm=" <KeyInfo> <SecurityTokenReference> <KeyIdentifier ValueType="X509v3"> BV4 </KeyIdentifier> </SecurityTokenReference> </KeyInfo> <CipherData> <CipherValue> BV5 </CipherValue> </CipherData> <ReferenceList> <DataReference URI="#enc" /> </ReferenceList> </EncryptedKey> </Security> </Header> <Body Id="body"> <EncryptedData Id="enc" Type=" <EncryptedMethod Algorithm=" /> <CipherData> <CipherValue> BV6 </CipherValue> </CipherData> </EncryptedData> </Body> </Envelope>

9 b Services Security: a preliminary study using Casper and FDR 09 Modelling WS-Security Construct a mapping φ from SOAP messages to Casper input, such that if a WS-security protocol contains the messages m 1, m 2..., m n then, 1. If an attack is found on φ(m 1 ), φ(m 2 ),..., φ(m n ) then a corresponding attack can be reproduced on m 1, m 2..., m n. 2. If an attack exists on m 1, m 2,..., m n then it also exists on φ(m 1 ), φ(m 2 ),..., φ(m n ) The more important of the above properties is (2), since we definitely do not want to generate a false proof of correctness using the translation. Any attack found by Casper can be translated back to make sure it is really present in the original protocol.

10 b Services Security: a preliminary study using Casper and FDR 10 Applying φ on a Security element φ( Security... /Security ) = φ( BinarySecurityToken... /BinarySecurityToken ), φ( EncryptedKey... /EncryptedKey ), φ( Signature... /Signature )

11 b Services Security: a preliminary study using Casper and FDR 11 Applying φ on a Signature element φ( Signature... /Signature ) = {φ( Reference /Reference ),... φ( Reference /Reference )...} φ( KeyInfo... /KeyInfo,SIG)

12 b Services Security: a preliminary study using Casper and FDR 12 Demonstrate the complete derivation of φ(m) φ(m) φ( Header... /Header ),φ( Body... /Body ) φ( Security... /Security ),φ( Body... /Body ) φ( BinarySecurityToken... /BinarySecurityToken ), φ( EncryptedKey... /EncryptedKey ), φ( Signature... /Signature ), φ( Body... /Body ) φ( EncryptedKey... /EncryptedKey ), φ( Signature... /Signature ), φ( Body... /Body ) φ( ReferenceList... /ReferenceList,{K}), {K} φ( KeyInfo... /KeyInfo,ENC), φ( Signature... /Signature ), φ( Body... /Body ) φ( DataReference URI=#enc /,{K}), {K} φ( KeyInfo... /KeyInfo,ENC), φ( Signature... /Signature ), φ( Body... /Body ) Context(enc,{K}), {K} φ( KeyInfo... /KeyInfo,ENC), φ( Signature... /Signature ), φ( Body... /Body ) Context(enc,{K}), {K} φ( SecurityTokenReference... /SecurityTokenReference,ENC), φ( Signature... /Signature ), φ( Body... /Body ) Context(enc,{K}), {K} φ( KeyIdentifier... /KeyIdentifier,ENC), φ( Signature... /Signature ), φ( Body... /Body ) Context(enc,{K}), {K} PK(B), {φ( Reference URI=#body... /Reference )},

13 b Services Security: a preliminary study using Casper and FDR 13 {φ( KeyInfo... /KeyInfo ),SIG}, φ( Body... /Body ) Context(enc,{K}), {K} PK(B), {φ( DigestMethod.../ )(φ(body))} φ( KeyInfo... /KeyInfo,SIG), φ( Body... /Body ) Context(enc,{K}), {K} PK(B), {sha1(φ(body))} φ( KeyInfo... /KeyInfo,SIG), φ( Body... /Body ) Context(enc,{K}), {K} PK(B), {sha1({body} φ( EncryptedData Id= enc... /EncryptedData ) )} φ( KeyInfo... /KeyInfo,SIG), φ( Body... /Body ) Context(enc,{K}), {K} PK(B), {sha1({body} K )} φ( KeyInfo... /KeyInfo,SIG), φ( Body... /Body ) Context(enc,{K}), {K} PK(B), {sha1({body} K )} φ( SecurityTokenReference... /SecurityTokenReference,SIG), φ( Body... /Body ) Context(enc,{K}), {K} PK(B), {sha1({body} K )} φ( Reference URI=#myCert.../,SIG), φ( Body... /Body ) Context(enc,{K}), {K} PK(B), {sha1({body} K )} SK(A), φ( Body... /Body ) Context(enc,{K}), {K} PK(B), {sha1({body} K )} SK(A), {Body} K {K} PK(B), {sha1({body} K )} SK(A), {Body} K

14 b Services Security: a preliminary study using Casper and FDR 14 Oasis proposed protocol 1. A B: M 2. B A: M After applying φ to both of the messages we get the following protocol. 1. MSG 1.A B : {K} PK(B), {sha1({body} K )} SK(A), {Body} K 2. MSG 2. B A : {K2} PK(A), {sha1({body2} K2 )} SK(B), {Body2} K2

15 b Services Security: a preliminary study using Casper and FDR 15 An attack Using FDR the following authentication attack was found. 1. MSG 1. I Bob : {K} PK(Bob), {sha1({body} K )} SK(I), {Body} K 2. MSG 2. Bob I : {K2} PK(I), {sha1({body2} K2 )} SK(Bob), {Body2} K2 3. MSG 1. Alice I Bob : {K3} PK(Bob), {sha1({body3} K3 )} SK(Alice), {Body3} K3 4. MSG 2. I Bob Alice : {K2} PK(Alice), {sha1({body2} K2 )} SK(Bob), {Body2} K2

16 b Services Security: a preliminary study using Casper and FDR 16 Future work Present a complete proof of φ s properties. We are interested in internalising potential intermediaries in order to be able to model and check protocols with arbitrary number of intermediaries. We will need to study what precise inferences we can draw for the WS-Security implementation in cases where Casper either finds no attacks on a small model or proves a protocol more generally.

17 b Services Security: a preliminary study using Casper and FDR 17 Thanks!

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