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Massachusetts Institute of Technology Handout 26.857: Network and Computer Security Septemb e r 11, 2006Professor Ronald L. Rivest Due: September 18, 2006Problem Set 1This problem set is due via email, to [email protected] on Monday, September 18 bythe beginning of class.You are to work on this problem set in groups of three or four people. Problems turned in by individuals,pairs, pentuples, etc. will not be accepted. Be sure that all group members can explain the s olutions. SeeHandout 1 (Course Information) for our policy on collaboration. If you do not have a group, let us know.Homework must be submitted electronically! Each problem answer must appear on a separate page. Markthe top of each page with your group member names, the course number (6.857), the problem set numberand question, and the date. We have provided templates for LATEX and Microsoft Word on the course website(see the Resources page).Grading and Late Policy: Each problem is worth 10 points. Late homework will not be acceptedwithout prior approval. Homework should not be submitted by email except with prior approval. (Somebodyfrom your group should be in class on the day that the homework is due.)With the authors’ permission, we will distribute our favorite solution to e ach problem as the “official”solution—this is your chance to become famous! If you do not wish for your homework to be used as anofficial solution, or if you wish that it only be use d anonymously, please note this on your homework.Problem 1-1. Security Policy.The California legislature has recently passed the Identity Information Protection Act, which requires thatstate-issued IDs that contain remotely-readable RFID chips must contain adequate security features toprevent them from being read by unauthorized parties. RFID chips are designed to store unique identifiersthat will be broadcast in response to a particular radio signal.The bill was motivated by concerns that these IDs might be remotely read without the user’s knowledge,revealing personal information that could b e used to commit fraud, identity theft, or gain unauthorizedaccess. To read more about the bill, its intent, and its motivations, got to the Resources page on the courseweb site and click on California RFID Bill Nears Approval.Your Task For this bill to be properly enforced the state must develop a security policy for RFID IDs.You are to help California lawmakers by writing your own short security policy for this scenario. Specifically,write a security policy for a state-issued ID card that includes an RFID meant to remotely communicate aunique identifier. The ID cards are to be used to facilitate efficient identification at pre-specified locations,including: airports, government services offices, and the Mexican border. Your security policy should takeinto account the concerns of the lawmakers (i.e., the IDs being remotely read without the user’s knowledgeleading to identity theft), but also not be too restrictive.For help on writing a sec urity policy go to the Resources page on the course web site and click on SampleSolutions from PS1 2003. See ques tion 1- 4, which asked students to develop a sec urity policy for either theMIT Card or Apple’s iPod. Sample solutions for both, as we ll as a short discussion from the TAs regardingcommon omissions, are included. These should help guide you in terms of content, format, and length.Problem 1-2. Remote Voti ngNed Nerdle has been thinking about the problem of “remote voting” (i.e. absentee voting, voting over thephone or over the Internet), and has come up with the following proposal.1. When each voter registers to vote, he/she must establish a 5-digit secret PIN with the election author-ities in his/her jurisdiction. This PIN is known only to the voter and to the election authorities. Thevoter is encouraged not to write his PIN down, but to memorize it. The voter can return to the townhall at any time if he wishes to change his PIN.2 6.857 : Handout 2: Problem Set 12. The PIN is used to establish a voter-specific “secret code” used for voting. Each element of the codeis also a 5-digit number, like the PIN. An element of the code represents “YES” if it agrees with thePIN in EXACTLY one position; otherwise it represents “NO”. Thus, there are5 ∗ 94= 32, 805possible ways of saying “YES” and100, 000 − 32, 805 = 67, 195possible ways of saying “NO”.3. When the voter votes, he uses random “YES” and “NO” codes to represent his votes. These may bewritten on the paper absentee ballot, entered on a phone keypad after each candidate’s name is read(if voting by phone), or entered in a browser form (if voting over the Internet).For example, if Alice’s PIN is “31415”, then her filled-in ballot:George Shrub: 27408John Carie: 82841Rolf Nadir: 31980represents a vote for George Shrub.Your Task Your assignment in this problem is to evaluate Nerdle’s proposed voting scheme. What mightNerdle be trying to accomplish? What pros (if any) or cons (if any) do you see for this scheme, with respectto security or other criteria, compared to existing remote voting schemes? Can you suggest modifications orimprovements to this proposal?Problem 1-3. MD5 Collisions In 2005, Wang and Yu published an attack on the MD5 hash function.Specifically, they discovered a technique that can efficiently produce collisions. See http://www.infosec.sdu.edu.cn/paper/md5-attack.pdf for the paper. The ability to produce collisions can introduce severesecurity vulnerabilities into schemes which depend on MD5 hash values as an indicator of integrity. Tohighlight the power of Wang and Yu’s attack, Daum and Lucks produced two postscript files with identicalMD5 hashes. When read, however, one is a letter of recommendation and the other is a security clearance!To see for yourself, download letter of rec.ps and order.ps from the Resources page of the course web site.View each file, then calculate their MD5 hash. Notice, we have made a Windows and Linux version of an MD5hash calculator available under Resources. The linux version, md5sum, is included in many distributions, soyou may not need to download it.Familiarize yourself with Daum and Lucks attack by reading the “How it Works” section of http://www.mathstat.dal.ca/~selinger/md5collision/, as well as the description on http://www.cits.rub.de/MD5Collisions/. You should then view the source code of the postscript files. You’ll notice that the


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