IT-Security (Chapter 4)

Question 1

Pseudonym Types

Answer 1

Person pseudonym
Role pseudonym
Relationship pseudonym
Role-relationship pseudonym
Transaction pseudonym

Question 2

Basics Techniques for Data Minimization

Answer 2

Anonymous Communication
Controlled Disclosure
Privacy enhanced ID Management Systems

Question 3

Anonymity

Answer 3

Anonymity of a subject means that the subject is not identifiable within a set of subjects, the anonymity set

Question 4

Global Attacker

Answer 4

• Observes all communication

* Observes some nodes

Question 5

Local Attacker

Answer 5

• Observers some communication

* Observes some nodes

Question 6

Implicit address

Answer 6

If message is directed to someone, it must contain an attribute so that recipient knows it is directed to him

Question 7

Explicit address

Answer 7

describes specific place in a network to which message should be delivered

Question 8

Mix

Answer 8

1. Collects messages,
2. Deletes duplicates,
3. Re-Codes,
4. Shuffles,
5. Forwards

Question 9

Pool mixes

Answer 9

Buffer (storage space) for n messages

1. Wait until n messages received
2. Select a message randomly and forward it

Question 10

Batch mixes

Answer 10

1. Fills up a buffer of size n

2. Send all n messages together but in random order

Question 11

What is the anonymity set size

Answer 11

Pool: number of messages
ever forwarded by mix at time t
Batch: batch size n

Question 12

Cascades: (Jondos)

Answer 12

analytical easy to understand
−anonymity set = batch size
all communication can be observed
−high traffic servers
−practical implementations of servers are imperfect

Question 13

Mix Nets (TOR)

Answer 13

less infrastructure needed
low traffic per node
lower assumptions about the servers
−hard to analyze (what is the anonymity set size?)

Question 14

DC Net

Answer 14

1. Toss a coin per neighbor (crown 0, head 1)

2. Broadcast XOR of all neighbor coins XOR your secret