Slide title

In CAPITALS

50 pt

Slide subtitle

32 pt

Muhammad Rizwan Asghar

August 14, 2019

PRIVACY AND ANONYMITY

Lecture 11

COMPSCI 316

Cyber Security

Source of most slides: Northeastern University, USA

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

2

FOCUS OF THIS LECTURE

Understand privacy and anonymity

Discuss solutions that offer privacy and

anonymity

Learn attacks on privacy and anonymity

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

3

MOTIVATION FOR PRIVACY

People have the right to keep their personal

data private

– Right to privacy

Privacy also means not to reveal information

about who is communicating with whom

The use of online services can pose a threat to

our privacy!

– There is a possibility to link users’ actions

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

4

MOTIVATION FOR ANONYMITY

Hiding identities of communicating parties from

each other or from third parties

Anonymity is a tool to preserve privacy

For many applications, a user identity might

not be needed by the service provider

– E.g., web browsing

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

5

USE OF ANONYMITY

Free speech for political and other comments

Whistleblowers

Journalists

Human rights activists

Normal users for avoiding tracking

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

6

ABUSE OF ANONYMITY

Disclosure of trade secrets

DoS

Other illegal activities by cybercriminals

– Illegal downloads

E.g., copyright infringement

– Scams

– Hacking

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

7

ARE YOU ANONYMOUS

Your IP address can be linked directly to you

– ISPs store communications record

– Data retention laws

You are being tracked

– Cookies

– Browser fingerprinting

– Device fingerprinting

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

8

QUANTIFYING ANONYMITY

How can we calculate how anonymous we

are?

Who sent this

message?

Suspects (Anonymity Set)

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

9

QUANTIFYING ANONYMITY

A larger anonymity set means stronger

anonymity

Source: pixabay.com

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

10

SOME TERMS

Unlinkability

– The inability of linking two or more items of

interest

E.g., packets, events, people, actions, etc.

– Three aspects

Sender anonymity: who sent?

Receiver anonymity: who is the destination?

Relationship anonymity: who communicates with

whom?

Unobservability

– The items of interest are indistinguishable from all

other items

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

11

PUBLIC KEY CRYPTO: REVISIT

Safe to distribute the public key KP

– Can only decrypt with the private key KS

– Computationally infeasible to derive KS from KP

<KP, KS>

KP

KP

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

12

ENCRYPTED DATA TRAFFIC

Content is unobservable

– Due to encryption

Source and destination are

trivially linkable

– No anonymity

Data Traffic

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

13

ANONYMISING PROXIES

Proxy Server

Using trusted centralised servers

Hides IP address of users

Users are not anonymous to proxy servers

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

14

ANONYMISING PROXIES:

SENDER ANONYMITY

Proxy Server

Source is unknown

Destination is known

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

15

ANONYMISING PROXIES:

RECEIVER ANONYMITY

Proxy Server

Source is known

Destination is unknown

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

16

ANONYMISING PROXIES:

MALICIOUS PROXY SERVER

Proxy Server

No anonymity

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

17

ANONYMISING PROXIES:

TRAFFIC ANALYSIS

Proxy Server

Statistical analysis of traffic patterns can compromise

anonymity, i.e., timing and/or volume of packets

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

18

SAMPLE QUESTION

Which one of the following statements is FALSE?

a) Data encryption provides unobservability

b) Anonymous proxy offers unlinkability

c) Both a & b

d) Data encryption guarantees anonymity

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

19

SAMPLE QUESTION: ANSWER

Which one of the following statements is FALSE?

a) Data encryption provides unobservability

b) Anonymous proxy offers unlinkability

c) Both a & b

d) Data encryption guarantees anonymity

Answer) d

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

20

DATA TO PROTECT

Personally Identifiable Information (PII)

– Name, address, phone number, etc.

OS and browser information

– Cookies

IP address

Amount of data sent and received

Traffic timing

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

21

MIX NETWORKS

Use a chain of anonymous proxies

Each proxy is known as a Mix

A mix receives messages from a set of

senders, shuffle them, and send to another mix

Originally designed for anonymous email

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

22

MIX PROXIES AND ONION ROUTING

Mixes form a cascade of anonymous proxies

Traffic is protected with layers of encryption

Mix

<KP, KS>

<KP, KS>

<KP, KS>

<KP, KS>

<KP, KS>

<KP, KS>

<KP, KS>

<KP, KS>[KP , KP , KP]

Encrypted

Tunnels

Non-encrypted

data

E(KP , E(KP , E(KP , M))) = C

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

23

ENCRYPTED PATH: ANOTHER VIEW

<KP, KS> <KP, KS> <KP, KS>

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

24

RETURN TRAFFIC

In a mix network, how can the destination respond to

the sender?

During path establishment, the sender places keys at

each mix along the path

– Data is re-encrypted as it travels the reverse path

<KP1 , KS1>

<KP2 , KS2>

<KP3 , KS3>

KP1 KP2KP3

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

25

TO BE CONTINUED

See the next lecture

Top right

corner for

field

customer or

partner logotypes.

See Best practice

for example.

Slide title

40 pt

Slide subtitle

24 pt

Text

24 pt

5

20 pt

26

Questions?

Thanks for your attention!