Cryptography and Data Protection

Cryptography and Data Protection Fall 2013

Part 1: Short Answer. Answers should be no longer than a few sentences. “Bulletized” lists or small tables may be used for the sake of brevity. (4 points each; partial credit may be given if work is clearly shown)

1. Give a specific example of how inference control might be implemented in a database.

Notes from Wikipedia: (1) An Inference Attack is a data mining technique performed by analyzing data in order to illegitimately gain knowledge about a subject or database.[1] A subject's sensitive information can be considered as leaked if an adversary can infer its real value with a high confidence. [2] This is an example of breached information security. An Inference attack occurs when a user is able to infer from trivial information more robust information about a database without directly accessing it.[3] The object of Inference attacks is to piece together information at one security level to determine a fact that should be protected at a higher security level.[4]

(2) Computer security inference control is the attempt to prevent users to infer classified information from rightfully accessible chunks of information with lower classification. Computer security professionals install protocols into databases to prevent inference attacks by software.Techniques to detect and remove inference channels can be organized into two categories. The first category includes techniques that detect inference channels during database design time. Inference channels are removed by modifying the database design or by increasing the classification levels of some of the data items. Techniques in the second category seek to eliminate inference channel violations during query processing time. If an inference channel is detected, the query is either refused or modified to avoid security violations.While design-time is easier to manage and implement, query-time approach allows more availability of data than in design-time approach because more information (past and present queries/answers) can be used for disclosure inference.Disclosure Monitor (DiMon) detects and eliminates inference channels based on database constraints.A Disclosure Inference Engine (DiIE) is proposed, that generates all information that can be disclosed based on a user’s previous query results, the current query results, and a set of Horn-clause constraints.Dynamic Disclosure Monitor (D2Mon) guarantees data confidentiality and maximal availability even in the presence of inferences and updates. It is our intention to complement an existing access control mechanism (e.g., DAC, MAC, RBAC) to address the inference problem.

MAC: In the Mandatory Access Control (MAC) model, users are given permissions to resources by an administrator. Only an administrator can grant permissions or right to objects and resources. Access to resources is based on an object's security level, while users are granted security clearance. Only administrators can modify an object's security label or a user's security clearance.

DAC: In the Discretionary Access Control (DAC) model, access to resources is based on user's identity. A user is granted permissions to a resource by being placed on an access control list (ACL) associated with resource. An entry on a resource's ACL is known as an Access Control Entry (ACE). When a user (or group) is the owner of an object in the DAC model, the user can grant permission to other users and groups. The DAC model is based on resource ownership.

RBAC: In the Role-Based Access Control (RBAC) model, access to resources is based on the role assigned to a user. In this model, an administrator assigns a user to a role that has certain predetermined right and privileges. Because of the user's association with the role, the user can access certain resources and perform specific tasks. RBAC is also known as Non-Discretionary Access Control. The roles assigned to users are centrally administered. Dynamic Disclosure Monitor Architecture uses this MAC to detect any direct security violation,if any direct security violation is detected the query is rejected then and there,otherwise it is passed through inference engine to disclose data that can be inferred.All the disclosed data obtained from inference engine is again sent to MAC to detect any direct security violation.If any violation is detected the query is rejected,otherwise answered.

2. For a public-key encryption system (such as PGP), list some reasons for and against using the same key pair for both encryption and signature.  List some reasons for using the same key pair for both encryption and signature  Against using the same key pair for both encryption and signature

http://security.stackexchange.com/questions/1806/why-should-one-not-use-the- same-asymmetric-key-for-encryption-as-they-do-for-sig

http://www.pgpi.org/doc/pgpintro/

3. Compare and contrast PKI and Kerberos.

4. PKI has not been widely successful, partly because users don’t trust digital signatures. Give some reasons for that distrust.

5. Suggest some ways to address the “crypto dilemma,” along with the pros and cons of each.

6. How might a hacker gain control of a victim’s PC, without having physical access? Please be specific.

7. Briefly describe the technical challenges that must be overcome when developing an effective virus checker.

8. As a means of improving security, a computer system stores hashes of passwords rather than the passwords. In the event that two different users use the same password, what can be done to assure that their passwords don’t result in the same hash?

9. e-commerce web sites often use a “shopping cart.” Describe a specific vulnerability that a hacker might exploit against an on-line shopping cart.

10. Compare and contrast Pretty Good Privacy, as we used it in our class this semester, and PKI.

11. If a secure communications system is trying to minimize bandwidth requirements through data compression, does the order (encrypt then compress vs. compress then encrypt) matter? Why or why not? 12. How can a secure telephone be protected against a man-in-the-middle attack?

13. You’ve been tasked by your boss to design a computer program that can detect encrypted files. List some ways that you could accomplish this.

14. Given that each PEM message is encrypted with its own per-message key, why is an initialization vector (IV) also provided? What RFC specifies the use of an IV?

15. Substantiate or refute the following statement: If there is a revocation process, public-key infrastructure (PKI) certificates do not need to contain an expiration date.

16. Briefly describe a situation where cryptographic techniques can aid the battle against malware. Describe a second situation where cryptographic techniques can hinder the battle against malware.

17. How can a system for multi-level access control be implemented for government and military applications? What might access rules look like for such a system?

18. Please concur with, dispute, or qualify the following statement. Performing a frequency analysis would be a good starting point for cracking an RSA-encrypted message. (Please be sure to include your rationale.)

19. What security features could be provided without changing the mail delivery infrastructure, i.e., by only running special software at the source and destination?

20. Computer system #1 requires logon passwords to be five upper-case letters. How many different passwords are there for system #1? Computer system #2 requires logon passwords to be five characters, which may be upper or lower-case letters, the numbers 0 through 9, and the special characters $ , %, and &. How many different passwords are there for system #2?

Part 2: Essay Question. Maximum length: three (3) pages. (20 pts.)

An enterprising group of entrepreneurs is starting a new cloud-like data storage and retrieval business, StoreItRite, Inc. For a fee, the new company will accept digitalized data (both text and images), and store it on hard drives at a data farm until needed by the customer. Customer data will be transmitted to and from StoreItRite over the Internet. StoreItRite guarantees that the data’s confidentiality and integrity will be maintained, and that client authentication will be provided.

StoreItRite also envisions some additional information assurance requirements for their internal operations. Company employees will need to exchange confidential email, and will need a mechanism for verifying the integrity and originator of email messages. Also, StoreItRite intends a daily backup of all customer data to a remote facility via a leased line. They wish to do so as economically as possible, while ensuring the data’s confidentiality and integrity.

StoreItRite is interviewing candidates for the position of Chief Information Officer (CIO). They are asking candidates to describe briefly how they would satisfy StoreItRite’s requirements as stated above, while minimizing risks to the clients’ data. How would a successful candidate respond? (Please note: StoreItRite is not asking CIO candidates to suggest specific commercial products to satisfy their requirements; rather, they are looking to assess the candidates’ overall knowledge of how cryptographic techniques can be used to satisfy their requirements.)