Dates, posted november 27th 2017, due december 7th, 2017, via email. Topic, how does context affect word recognition? Synthesize the problem and the evidence for an intelligent non-expert (language scientist). We have examined in detail the question of how words are recognized in context. This has taken us on a tour of different experimental paradigms and literatures, sometimes considering apparently contradictory findings. . For this final assignment of the semester, please give a brief synopsis of what we should conclude from this literature. . Do different experimental measures lead us to a consistent view on how context affects word recognition? This should be no longer than 3 pages (single spaced).
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Explain how a clever Trojan horse with access to the secret source code on m can collude with another machine on the Internet to leak the source code, even without access to the hardware authentication device. This assignment was locked Sep 30, 2017 at 12:10am. Homework notebook : cs109a_hw2.ipynb, datsets needed: dataset_1_test. Txt, you have the option to submit in propagandist pairs. Recall how to submit in pairs: Click people in the navbar, click the Groups tab. Type in the search box: HW_ (replace _ with the homework number, hw2 in our case choose an empty group and have both members in your pair click. Warning: If you are submitting in a pair: both members must join a canvas group before they submit and before the homework deadline for on time submissions, whichever is earlier. If your group is not in place when you submit or if you submit after the assignment deadline, then you are submitting alone. This is a canvas limitation. For more: read the, instructions for Submitting Homework).
People suspect that the problem is caused by attempts to create tcp connections to the outside world, which instead of failing instantly take approximately one minute. After all, clients' tcp implementations treat packets dropped great by the firewall policy just the same as packets dropped because of congestion-they back off and keep trying. To solve the problem, the administrators re-configure their routers not just to drop packets silently, but in certain cases to send packets back to the source of a dropped packet. Describe precisely what the routers can send back to make prohibited outgoing tcp connections fail quickly. (Assume they cannot make any changes to the tcp implementation on clients.) After the fix from the previous part, things improve somewhat, but applications are still locking. It is determined that the problem is dns lookups to the outside world, which are also taking a long time to fail. To solve the problem, the administrators run a caching resolver on gatekeeper, and configure all the internal clients to use gatekeeper as their dns nameserver. The administrators figure that since dns is a read-only protocol, it is safe to allow internal machines to query for ip addresses of hosts anywhere on the Internet, as long as any actual communication to those ip addresses is blocked by the routers. Where is the flaw in the administrators' logic?
Employees can log into gatekeeper from internal machines using ssh and their hardware authentication device. From gatekeeper, they can ssh to the rest of the Internet. All other machines at the company are on a separate subnet 24) and can exchange packets with gatekeeper but not with the outside world. Machines on the outside Internet should not be able to ssh to gatekeeper. Describe how to enforce this policy with stateless packet filtering on router A and/or router. Describe the precise packet filtering rules you would put in place at each router. You may assume that the routers only forward ipv4 traffic. After several days of this new policy, employees become annoyed that many applications seem to lock up for periods of a minute.
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Is this method vulnerable to dictionary attack by an eavesdropper? If so explain how; if not explain why not. Suppose the writing protocol is run over ssl (where the ssl session was authenticated using the server's certificate). Is the resulting protocol vulnerable to dictionary attack by an eavesdropper? Is the resulting protocol vulnerable to a man written in the middle attack?
You may assume that users ignore any ssl warning pop-up and click "continue" to proceed. Suppose the protocol is run over ssl as in part (b but the browser uses the following key kb to compute the mac: Kb (pwd) (client-ssl-session-key) where denotes concatination and client-ssl-session-key is the ssl session key currently used by the browser. The server checks the mac using the following key: Ks (pwd) (server-ssl-session-key) where server-ssl-session-key is the ssl session key currently used by the server. Is the resulting protocol vulnerable to your attacks from part (b)? Problem 5 - firewalls Consider a company, m, with the following network topology: m is extremely paranoid about the prospect of a trojan horse surreptitiously sending the source code of their product out over the network. Therefore, they issue every employee a small hardware authentication device, and wish to require that any communication to the outside world be authenticated by a human typing in a security code computed by and displayed on this authentication device. To enforce the policy, the administrators set up a single machine, m, that can talk both to internal company machines and to the rest of the Internet.
Recall that the smtp protocol runs on top of tcp. You may assume that the victim mail server generates random and unpredictable tcp sequence numbers for new connections. Suppose a certain mail server generates tcp sequence numbers for new connections using a predictable algorithm, say the initial sequence number for connection i is simply the number. Explain exactly how a spammer can fool the mail server into accepting spam from it by spoofing source ip addresses in packets. Recall that smtp is an interactive protocol. An smtp transcript looks as follows: Sender: mail from: mail Serv: 250 ok, sender: rcpt to: mail Serv: 250 ok sender: data mail Serv: 354 End data with.
Sender: Some message data second line. Mail Serv: 250. And the message is delivered. You may assume that the smtp pipelining extension is allowed by the mail server. Problem 4 - dictionary attacks and mitm in class we discussed an authentication method called challenge-response for authenticating a user to a server. At a high level, the basic mechanism works as follows: Browser Server - i am user Alice pwd Nonce n pwd check mac the following questions ask whether various attackers can impersonate the user and login to the server on behalf of the user.
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Suppose the web system displays incoming email messages in a web browser using the following html sketch: html body - headers - div id"msg" - verbatim Email Message - /div /body /html give an example email message you could send to a user of this. You may assume the web system uses a cookie called SessionID to authenticate user requests after user login. How could the web-based email system defend against such attacks? Problem 3 - tcp sequence numbers. Suppose a spammer sends spam email from ip you address. This ip address is quickly lab added to a blacklist and mail servers ignore all emails from this ip address. Can the spammer evade the blacklisting mechanism by sending packets with a spoofed source ip address?
CS155 Homework #2, due: Thursday, may 17, problem 1 - cookies. A web server requires each user to log. However, the implementers of the web site are worried about storing passwords on the server, since they are afraid someone might break in and steal them. Therefore, they decide to use a clever idea. When a user creates an account, the account number is stored on the server and the user's password is stored in a cookie on the user's machine. Then, when the user tries to log in later, the server compares the password typed in by the user with the password stored in the user's cookie. Assuming that the implementers have not thought of any other clever ideas, how would you log into another users account without knowing their password? Describe at least one method that you could for use to keep passwords in cookies (and not on the server but prevent the attack you devised in part (a)? Problem 2, consider a broken web-based mail system.
the values in the constructor. In each thread calculate one element (i.e., multiply the elements of one raw from a and one column from b, and add the results to get the value. The main thread should wait until all the other threads are done and then print the matrix C / file: Matrix. Util.Random; public class Matrix public static int a, b, c; public int n; public void printMatrix(int M) for(int i 0; i n; i) for(int j 0; j n; j) int t"Mij intln public Matrix n 3; a new intnn; b new intnn; c new intnn;. Aij xtInt 10; / keep numbers below. Bij xtInt 10; public void doWork multThread mt new MultThreadnn; for(int i 0; i n; i) for(int j 0; j n; j) mtij new MultThread(3, i, j art try for(int i 0; i n; i) for(int j 0; j n; j) in catch(InterruptedException ie) intln. Java public class MultThread extends Thread private int n; / n*n matrix private int i, j; / row, column public MultThread(int size, int ii, int jj) n size; i ii; j jj; public void run j 0; for(int x 0; x n; x). (10pts) Scheduling: given the following mix of job, job lengths, and arrival times, assume a time slice of 10 and compute the completion and average response time of each job for the fifo, rr, and srtf algorithms. Use the following format for the solution: Assume the ready queue is empty. Parameters Scheduling Algorithms Job length arrival time fifo rr srtf avg.
Its easy for threads to inadvertently disrupt each other since they share the entire address space. Process consumes more resources. (5pts) Threads: Assume that the os implements Many-to-many multithreading model. What is the minimum number of kernel threads required to achieve better concurrency than in the many-to-One professional model? At least two kernel threads are required to achieve better concurrency in the many-to many model than in the many-to-One model. With more than two kernel threads, cpu can still schedule other threads for execution when one threads is performing a blocking system calls. (10pts) Threads: What is the relation between Solaris user threads and java application threads in a solaris environment? In Solaris.6, the many-to-many model is implemented. . Typically, a java application thread is implemented using a user-level thread in Solaris.
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Homework 2 Solution. . (10pts) Threads: What is the difference between a process and a thread. Which one consumes more resources? A process defines surgery the address space, text, resources, etc. A thread defines a single sequential execution stream within a process. Threads are bound to a single process. Each process may have multiple threads of control within. Its much easier to communicate between threads than between processes.