Suppose Bob joins a BitTorrent torrent, but he does not want to upload any data to any other peers (so called free-riding). a. Bob claims that he can receive a complete copy of the file that is shared by the swarm. Is Bob's claim possible? Why or why not? b. Bob further claims that he can further make his "free-riding" more efficient by using a collection of multiple computers (with distinct IP addresses) in the computer lab in his department. How can he do that?

Suppose Bob joins a BitTorrent torrent, but he does not want to upload any data to any other peers (so called free-riding). a. Bob claims that he can receive a complete copy of the file that is shared by the swarm. Is Bob's claim possible? Why or why not? b. Bob further claims that he can further make his "free-riding" more efficient by using a collection of multiple computers (with distinct IP addresses) in the computer lab in his department. How can he do that?

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Approximately how many bits of entropy does a password consisting of five random English words have?
Suppose we have a very short secret s (e.g., a single bit or even a Social Security number), and we wish to send someone else a message m now that will not reveals but that can be used later to verify that we did know s. Explain why m = MD5(s) or m = E(s) with RSA encryption would not be secure choices, and suggest a better choice.
Suppose Alice and Bob store their RSA public keys in a file on a server. Theycommunicate regularly using authenticated and confidential messages. Eve wants to readthe messages but is unable to crack the RSA private keys of Alice and Bob. However, Eve canbreak into the server and alter the file containing Alice’s and Bob’s public keys.a. How should Eve alter that file so that she can read confidential messages sent fromBob to Alice?b. How might Alice and/or Bob detect Eve’s subversion of the public keys?
Computer Science * Alice and Bob are conducting Diffie-Hellman key exchange with the parameters p = 101 and a = 2. Their parameters are small and we decide to crack the key exchange. Suppose Alice is observed sending public key A = 79 and Bob sends public key B = 26. a) What is Alice's private key? b) What is Bob's private key? c) What is the shared secret? Alice and Bob are using the EIGamal cipher with the parameters p = 29 and a = 2. %3D Their parameters are small and we decide to crack the cipher. Suppose Alice is observed sending public ephemeral key kE 25 and Bob sends public key 3 = 4. %3D Alice is observed transmitting the ciphertext y = 13. a) What is the masking key kM? b) What is the plaintext?
Suppose Alice has a public key with modulus 815153 and encryption exponent 91. Eve intercepts a ciphertext 766247from Bob that was encrypted using this key. She calculates 766247⋅941^91(mod815153)=143804 and asks Alice to decrypt this message as an authentication test. Alice responds with the decrypted message 167698 Find the plaintext without factoring Alice’s modulus.
Consider a very simple symmetric block encryption algorithm in which 32-bits blocks of plaintext are encrypted using a 64-bit key. Encryption is defined as C = (PK₁) K₁ where C = ciphertext, K = secret key, Ko = leftmost 64 bits of K, K₁ = rightmost 64 bits of K,+ = bitwise exclusive OR, and is addition mod 264. a. Show the decryption equation. That is, show the equation for P as a function of C, Ko, and K₁. b. Suppose and adversary has access to two sets of plaintexts and their correspond- ing ciphertexts and wishes to determine K. We have the two equations: C = (PK) K₁; C = (PK) K₁ First, derive an equation in one unknown (e.g., Ko). Is it possible to proceed fur- ther to solve for Ko?
Consider the following sequence of commands and messages: $ git clone git:cisc210/example Cloning into 'example'... remote: Counting objects: 19, done. remote: Compressing objects: 100 % (12/12), done. remote: Total 19 (delta 1), reused 0 (delta 0) Receiving objects: 100 % (19/19), done. Resolving deltas: 100 % (1/1), done. $ touch sky $ git add sky fatal: not a git repository (or any parent up to mount point /) Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set). Enter two commands that would make it so the 'git add' wouldn't fail. Note: don't actually execute the "git add" command, just two commands that would let it work. Feel free to try it out on cisc210.cis.udel.edu!
Suppose Alice has a public key with modulus 815153 and encryption exponent 91. Eve intercepts a ciphertext 766247 from Bob that was encrypted using this key. She calculates 766247 941 (mod 815153)= 143804 and asks Alice to decrypt this message as an authentication test. Alice responds with the decrypted message 167698 Find the plaintext without factoring Alice's modulus.
Suppose Alice has r and w rights over the file book. Alice wants to copy r rights to book to Bob. Assuming there is a copy right c, write a command to do this. Now assume the system supports a copy flag; for example, the right r with the copy flag would be written as rc. In this case, write a command to do the copy. In the previous part, what happens if the copy flag is not copied?
Suppose Alice and Bob have RSA public keys in a file on a server. They communicate regularly, using authenticated, confidential message. Eve wants to read the messages but is unable to crack the RSA private keys of Alice and Bob. However, she is able to break into the server and alter the file containing Alice’s and Bob’s public keys. 1) How should Eve alter the file to so that she can read confidential messages sent between Alice and Bob, and forge messages from either? 2) How might Alice and/or Bob detect Eve’s subversion of the public keys?
Compute the vocabulary size M for this scenario: Looking at a collection of web pages, you find that thereare 3000 different terms in the first 10,000 tokens and30,000 different terms in the first 1,000,000 tokens. Assume a search engine indexes a total of 20,000,000,000(2 × 1010) pages, containing 200 tokens on average What is the size of the vocabulary of the indexed collectionas predicted by Heaps’ law? Please type answer no write by hend.
Alice and Bod have decided to use a symmetric encryption algorithm. They have some assumptions about their messages:- Messages only contain capital letters (i.e. A to Z)- The length of their shared key must be greater than or equal to the length of the plaintext- They assign each letter a number as follows: (A,0), (B,1), (C,2), (D,3),…, (Z,25)Their algorithm combines the key and the message using modular addition. The numerical values of corresponding message and key letters are added together, modulo 26. For example, if the plain text is “HELLO” and the key is “SECRET” then the encrypted message is calculated as following:Since the length of the plaintext is 5, we just need the first 5 letters of the key (i.e. “SECRE”), then for each letter, we should add corresponding letters in both the plaintext and the key modulo 26.Plaintext: H (7) E (4) L (11) L (11) O (14)Key: S (18) E (4) C (2) R (17) E(4)Cipher: Z (25) I (8) N(13) C(2) S (18) Write a program in Python, C/C++ or JavaScript to…