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Anonymity, unobservability, pseudonymity and identity management requirements

for an AmI world

Andreas Pfitzmann

Dresden University of Technology, Department of Computer Science, D-01062 DresdenPhone: 0351/ 463-38277, e-mail: pfitza@inf.tu-dresden.de, http://dud.inf.tu-dresden.de/

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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.

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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.

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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.

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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

availabilityfor authorized users

≥ total correctness

partial correctness

no classification, but pragmatically usefulexample: unauthorized modification of a program

1) cannot be detected, but can be prevented; cannot be reversed2)+3) cannot be prevented, but can be detected; can be reversed

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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 can’t check whether your trust has been justified

even after the fact vs. you can check whether your

trust has been justified.

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Transitive propagation of errors and attacks

symbol explanation

computer

program

A used B todesign C

machine X exe-cutes program Y

Y

X

A

B C

transitivepropagation of “errors”

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Trojan horseuniversal

(covert)

input channel

universalcommands

Trojan horse

(cov

ert)

outp

ut c

hann

el

write access

write access

non-termination

resource consumption

unauthorized disclosure of information

unauthorizedmodification of information

unauthorized withholding of information or resources

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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 ...

faulttolerance

Trojan horse • universal • transitive

includes user,operator, service and maintenance ... of the system used

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protection concerningprotection against

to achievethe intended

to preventthe 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 loglogical access

intermediate languages and intermediate results, which are analyzed independently

independent analysis of the productsee 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

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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.

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Protection Goals: Sorting

ContentContent CircumstancesCircumstances

ConfidentialityConfidentialityHidingHiding

Integrity Integrity

AnonymityAnonymityUnobservabilityUnobservability

AccountabilityAccountability

Prevent the Prevent the unintendedunintended

Achieve the Achieve the intendedintended

Availability Availability ReachabilityReachabilityLegal EnforceabilityLegal Enforceability

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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 sender’s 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.

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Correlations between protection goals

ConfidentialityConfidentiality

HidingHiding

IntegrityIntegrity

AnonymityAnonymity

UnobservabilityUnobservability

AccountabilityAccountability

AvailabilityAvailabilityReachabilityReachability

Legal EnforceabilityLegal Enforceability

weakens–

–

implies strengthens+

+

+

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Golden rule

Correspondence between organizational and IT structures

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.

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Superposed sending (DC-network)

+

+++

........

+

........

station 1 M1 3A781

M2 00000

M3 00000

+

........

station 2

+

........

station 3

K23 67CD3

K12 2DE92

K13 4265B

-K12 E327E

-K13 CEAB5

-K23 A943D

67EE2

4AE41

99B6E

anonymous access= M1 M2 M3+ +

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

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Protection of the communication relation: MIX-network

MIX1 batches, discards repeats,

MIX2 batches, discards repeats,

D.Chaum 1981 for electronic mail

c1 (z4,c2(z1,M1)) c1 (z5,c2(z2,M2)) c1 (z6,c2(z3,M3))

c2 (z3,M3) c2 (z1,M1) c2 (z2,M2)

M2 M3 M1

d1(c1(zi,Mi)) = (zi,Mi)

d2(c2(zi,Mi)) = (zi,Mi)

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Identity management

Privacy-enhancing identity management is only possible

w.r.t. parties which don‘t 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).

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Personal identifier

845 authorizes A: ___

A notifies 845: ___

845 pays B €

B certifies 845: ___

C pays 845 €

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Role-relationship pseudonyms and transaction pseudonyms

762 authorizes A: __

A notifies 762: ___

451 pays B €

B certifies 451: ___

B certifies 314: ___

C pays 314 €

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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

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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)

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Pseudonyms: Use in different contexts => partial order

A  B stands for “B enables stronger anonymity than A”

increasingunlinkability

of transactions

increasingavailable

anonymity

linkable

unlinkable

person pseudonym

role pseudonym relationship pseudonym

role-relationship pseudonym

transaction pseudonym

number of an identity card, social security number, bank

account

pen name, employee identity card number

customer number

contract number

one-time password, TAN

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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.

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Terminology and further reading

http://dud.inf.tu-dresden.de/Anon_Terminology.shtml