1. 1 Representing Identity CSSE 490 Computer Security Mark Ardis, Rose-Hulman Institute April 19, 2004

2. 2 Overview Certificates Network identities Remailers

3. 3 What is Identity? Def: A principal is a unique entity. An identity specifies a principal. A principal may be a person, an organization, or an object

4. 4 Example Identities URL File name File descriptor Login User Identification Number (UID)

5. 5 Certificates Used to bind crypto keys to identifiers Certification Authority (CA) vouches for identity of principal to which certificate is issued CA authentication policy describes level of authentication required to identify principal when certificate issued CA issuance policy describes principals to whom CA will issue certificates

6. 6 Internet Policy Registration Authority (IPRA) Sets policies for all subordinate CAs Certifies Policy Certification Authorities (PCAs) – each may have their own authentication and issuance policy – may not conflict with IPRA PCAs issue certificates to CAs CAs issue certificates to organizations and individuals

7. 7 Network Identities Media Access Control (MAC) address used at link layer Internet Protocol (IP) address used at network layer Host name used at application layer Dynamic Host Configuration Protocol (DHCP) may be used to temporarily assign an IP address

8. 8 Domain Name System (DNS) Records Forward: map host name to IP address Reverse: map IP addresses to host names May compare forward and reverse mappings in order to determine whether to trust a host name

9. 9 Cookies Used to represent state of a web session Fields: – Name, value: bind value to name – Expires: delete at end of session or at specified time – Domain: to whom cookie may be sent, must have embedded "." – Path: restricts domain – Secure: whether to use SSL

10. 10 Anonymity on the Web Pseudo-anonymous remailer - replaces originating email address before forwarding, keeps mapping of anonymous identities and associated origins Cypherpunk remailer (type 1) - deletes header of incoming message and forwards remainder – typically used in chain – typically enciphered messages

11. 11 Attacking Cypherpunk Monitor traffic in/out of remailers Observe times of arrival/departure Observe size of messages Flood remailer with messages to defeat countermeasures

12. 12 Mixmaster Remailers (Type 2) Cypherpunk remailer plus: – padding or fragmentation to create fixed size records – uniquely numbered messages to avoid replay attacks

13. 13 Why is Anonymity Needed? Whistleblowing Protection of privacy ???