1. Anonymity - Background
R. Newman

2. Topics Defining anonymity Need for anonymity Defining privacy
Threats to anonymity and privacy
Mechanisms to provide anonymity
Applications of anonymity technology

3. Anonymity Mechanisms Cryptography Steganography
Traffic Analysis Prevention (TAP)
Mixes, crowds
Data sanitization/scrubbing
k-anonymity

4. Security Security is relative Must know what we want
Relative to security goals
Relative to threats (adversaries)
Must know what we want
Must know what we are up against
Must understand what we have to work with

5. Adversaries Global vs. Restricted Passive vs. Active
All links vs. some links
All network nodes vs. some or no nodes
Passive vs. Active
Passive – listen only
Active – remove, modify, replay, or inject new messages
Cryptography Assumptions
All unencrypted contents are observable
All encrypted contents are not, without key

6. Symmetric Key Cryptography
One key, Kab, associated with entities A and B
Same key used for encryption and decryption:
C=E(M,Kab),
M=D(C,Kab)=D(E(M,Kab)Kab)
For message M, ciphertext C = {M}K
Anyone with Kab can form ciphertext
Anyone with Kab can decrypt C

7. Symmetric Key Cryptography
One key, Kab, associated with entities A and B
For message M, MIC or MAC uses hash fcn
If only A and B have Kab, then MAC
(authentication, not non-repudation)
If group key, then MIC
(integrity check, but not authentication)
Depending on E, may require crypto hash fcn

8. Public Key Cryptography
Two keys, K and K-1, associated with entity A
Hard to get K-1 from K and vice versa (unless...)
K is public key, K-1 is private key
Keys are inverses: {{M}K}K-1 = {{M}K-1}K = M
For message M, ciphertext C = {M}K
Anyone can send A ciphertext using K
Only A has K-1 so only A can decrypt C
For message M, signature S = {M}K-1
Anyone can verify M,S using K
Only A can sign with K-1

9. Details we omit Limit on size of M, based on size of K
Need to format M to avoid attacks on PKC
Use confounder to foil guessed ptxt attacks
Typical use of one-way hash H to distill large M to reasonable size for signing
Typical use of PKC to distribute symmetric key for actual encryption/decryption of larger messages
See for standards

10. Next
Cover Chaum Mixes
Mix Cascades
Types of mixes