1. 1 Anonymity, unobservability, pseudonymity and identity management requirements for an AmI world Andreas Pfitzmann Dresden University of Technology, Department of Computer Science, D-01062 Dresden Phone: 0351/ 463-38277, e-mail: pfitza@inf.tu-dresden.de, http://dud.inf.tu-dresden.de/pfitza@inf.tu-dresden.dehttp://dud.inf.tu-dresden.de/

2. 2 Excerpts from: Treaty Establishing a Constitution for Europe Article I-2 The Union's values The Union is founded on the values of respect for human dignity, freedom, democracy, equality, the rule of law and respect for human rights, including the rights of persons belonging to minorities.... Article I-3 The Union's objectives 2. The Union shall offer its citizens an area of freedom, security and justice without internal frontiers, and an internal market where competition is free and undistorted.

3. 3 Excerpts from: Treaty Establishing a Constitution for Europe Article II-68 Protection of personal data 1.Everyone has the right to the protection of personal data concerning him or her. 2.Such data must be processed fairly for specified purposes and on the basis of the consent of the person concerned or some other legitimate basis laid down by law. Everyone has the right of access to data which has been collected concerning him or her, and the right to have it rectified.

4. 4 Distrust is the basis Cooperation on the basis of mutual distrust (e.g. separation of powers, checks and balances) is the basis of organizing modern societies, not trust.

5. 5 Threats and corresponding protection goals threats: 1) unauthorized access to information 2) unauthorized modification of information 3) unauthorized withholding of information or resources protection goals: confidentiality integrity availability for authorized users total correctness partial correctness no classification, but pragmatically useful example: unauthorized modification of a program 1) cannot be detected, but can be prevented;cannot be reversed 2)+3) cannot be prevented, but can be detected;can be reversed

6. 6 Distrust is the basis, revisited Cooperation on the basis of mutual distrust (e.g. separation of powers, checks and balances) is the basis of organizing modern societies, not trust. Cf. confidentiality vs. integrity / availability : You cant check whether your trust has been justified even after the fact vs. you can check whether your trust has been justified.

7. 7 Transitive propagation of errors and attacks symbol explanation computer program A used B to design C machine X exe- cutes program Y Y X A B C transitive propagation of errors

8. 8 Trojan horseuniversal (covert) input channel universal commands Trojan horse (covert) output channel write access write access non-termination resource consumption unauthorized disclosure of information unauthorized modification of information unauthorized withholding of information or resources

9. 9 Protection against whom ? Laws and forces of nature - components are growing old - excess voltage (lightning, EMP) - voltage loss - flooding (storm tide, break of water pipe) - change of temperature... Human beings - outsider - user of the system - operator of the system - service and maintenance - producer of the system - designer of the system - producer of the tools to design and produce - designer of the tools to design and produce - producer of the tools to design and produce the tools to design and produce - designer... fault tolerance Trojan horse universal transitive includesuser, operator, service and maintenance... of the system used

10. 10 protection concerning protection against to achieve the intended to prevent the unintended designer and producer of the tools to design and produce designer of the system producer of the system service and maintenance user of the system outsiders unobservability, anonymity, unlinkability: avoid the ability to gather unnecessary data physical and logical restriction of access protect the system physically and protect data cryptographically from outsiders restrict physical access, restrict and log logical access intermediate languages and intermediate results, which are analyzed independently independent analysis of the product see above + several independent designers control as if a new product, see above operator of the system Which protection measures against which attacker ? physical distribution and redundance

11. 11 Multilateral security Security with minimal assumptions about others Each party has its particular protection goals. Each party can formulate its protection goals. Security conflicts are recognized and compromises negotiated. Each party can enforce its protection goals within the agreed compromise.

12. 12 Protection Goals: Sorting ContentCircumstances ConfidentialityHiding Integrity AnonymityUnobservability Accountability Prevent the unintended Achieve the intended Availability Reachability Legal Enforceability

13. 13 Protection Goals: Definitions Confidentiality ensures the confidentiality of user data when they are transferred. This assures that nobody apart from the communicants can discover the content of the communication. Hiding ensures the confidentiality of the transfer of confidential user data. This means that nobody apart from the communicants can discover the existence of confidential communication. Anonymity ensures that a user can use a resource or service without disclosing his/her identity. Not even the communicants can discover the identity of each other. Unobservability ensures that a user can use a resource or service without others being able to observe that the resource or service is being used. Parties not involved in the communication can observe neither the sending nor the receiving of messages. Integrity ensures that modifications of communicated content (including the senders name, if one is provided) are detected by the recipient(s). Accountability ensures that sender and recipients of information cannot successfully deny having sent or received the information. This means that communication takes place in a provable way. Availability ensures that communicated messages are available when the user wants to use them. Reachability ensures that a peer entity (user, machine, etc.) either can or cannot be contacted depending on user interests. Legal enforceability ensures that a user can be held liable to fulfill his/her legal responsibilities within a reasonable period of time.

14. 14 Correlations between protection goals ConfidentialityHiding Integrity AnonymityUnobservability Accountability Availability Reachability Legal Enforceability weakens – – implies strengthens + + +

15. 15 Golden rule Correspondence between organizational and IT structures Since tamper-resistance of HW is all but good and organizations are far from perfect keeping secrets: Personal data should be gathered, processed and stored, if at all, by IT in the hands of the individual concerned.

16. 16 Superposed sending (DC-network) + + ++........ +........ station 1 M 1 3A781 M 2 00000 M 3 00000 +........ station 2 +........ station 3 K 2 3 67CD3 K 1 2 2DE92 K 1 3 4265B -K 1 2 E327E -K 1 3 CEAB5 -K 2 3 A943D 67EE2 4AE41 99B6E anonymous access = M 1 M 2 M 3 + + User station Pseudo-random bit-stream generator Modulo- 16-Adder Anonymity of the sender If stations are connected by keys the value of which is completely unknown to the attacker, tapping all lines does not give him any information about the sender. D. Chaum 1985 for finite fields A. Pfitzmann 1990 for abelian groups 3A781

17. 17 Protection of the communication relation: MIX-network MIX 1 batches, discards repeats, MIX 2 batches, discards repeats, D.Chaum 1981 for electronic mail c 1 (z 4,c 2 (z 1,M 1 )) c 1 (z 5,c 2 (z 2,M 2 ))c 1 (z 6,c 2 (z 3,M 3 )) c 2 (z 3,M 3 ) c 2 (z 1,M 1 )c 2 (z 2,M 2 ) M2M2 M3M3 M1M1 d 1 (c 1 (z i,M i )) = (z i,M i ) d 2 (c 2 (z i,M i )) = (z i,M i )

18. 18 Identity management Privacy-enhancing identity management is only possible w.r.t. parties which dont get GUIDs anyway, by the communication network (e.g. network addresses) the user device (e.g. serial numbers, radio signatures), or even the user him/herself (e.g. by biometrics).

19. 19 Personal identifier 845 authorizes A: ___ A notifies 845: ___ 845 pays B B certifies 845: ___ C pays 845

20. 20 Role-relationship pseudonyms and transaction pseudonyms 762 authorizes A: __ A notifies 762: ___ 451 pays B B certifies 451: ___ B certifies 314: ___ C pays 314

21. 21 Pseudonyms: Linkability in detail Distinction between: 1. Initial linking between the pseudonym and its holder 2. Linkability due to the use of the pseudonym in different contexts

22. 22 Pseudonyms: Initial linking to holder Public pseudonym: The linking between pseudonym and its holder may be publicly know from the very beginning. Initially non-public pseudonym: The linking between pseudonym and its holder may be know by certain parties (trustees for identity), but is not public at least initially. Initially unlinked pseudonym: The linking between pseudonym and its holder is – at least initially – not known to anybody (except the holder). Phone number with its owner listed in public directories Bank account with bank as trustee for identity, Credit card number... Biometric characteristics; DNA (as long as no registers)

23. 23 Pseudonyms: Use in different contexts => partial order A B stands for B enables stronger anonymity than A number of an identity card, social security number, bank account pen name, employee identity card number customer number contract number one-time password, TAN

24. 24 Summing up Requirements for a multilaterally secure and privacy- enabling AmI world: Make sure that others cannot gather unnecessary data (just not gathering it is not enough, as history tells us). Since trust in foreign infrastructures w.r.t. confidentiality properties (e.g. privacy) will be very limited at best, each human should have his/her trusted device(s) to provide for his/her security. This device might act in an ambient way in the interests of its owner. Communication of humans with their ICT-environment should be by means of their trusted device only. Develop trusted devices which have no identifying radio signature. Minimize sensor abilities w.r.t. sensing foreign human beings directly.

25. 25 Terminology and further reading http://dud.inf.tu-dresden.de/Anon_Terminology.shtml