COMP 424 Midterm 1

Choose one which is NOT required to make the One-Time Pad unbreakable.

The key is at least as long as the message that must be encrypted

The key is truly random

Each key is used only once

The key is chosen from very long texts such as a book

Choose one that does NOT describe the Stream Ciphers correctly.

Stream cipher is a symmetric key cipher

Each plaintext digit is encrypted one at a time with the corresponding digit of the keystream, to give a digit of the ciphertext stream

Stream Ciphers has perfect secrecy like One-Time Pad has

In practice, a digit is typically a bit and the combining operations is an exclusive-or (XOR)

What is the weakness of Electronic Code Book (ECB) encryption mode?

When one block changes, all later blocks also need to change

Reveals patterns of data when a data block repeats

Uses an arbitrary number that changes with each block of text encrypted

Because all the blocks are chained, it takes a long time to encrypt

Choose the wrong description about UNIX access control

There should be a one-to-many mapping from principals to users

The execution bit controls traversing a directory

Write + Execution control creates/deletes files in the directory

The final r/w/x bits of a file applies for others (not owner, not group

The Kasisky test for finding key length in Vigenere cipher is based on the observation that two identical segments of plaintext, will be encrypted to the same ciphertext, if they occur in the text at a distance ^ such that ^ is a multiple of m, the key length.

True

False

Cross Site Scripting can occur when the web applications take user inputs that contain scripts and use them as part of the webpage

True

False

As a prevention of SQL injection attack, parameterized queries make it possible for the database to recognize the code and distinguish it from input data

True

False

When the system uses 128 bits of AES key for block cipher, to ensure collision resistance, how long of a hash output do you require to satisfy the Weakest Link Principle?

What access control principle does the following sentences describe? "This principle requires that all accesses to objects be checked to ensure they are allowed. Whenever a subject attempts to read an object, the operating system should interpose the action. First, it determines if the subject can read the object. If so, it provides the resources for the read to occur. If the subject tries to read the object again, the system should again check that the subject can still read the object."

What do the following sentences describe? "Guarded gates from user mode (space, land) into kernel mode (space, land). They change processor state from user mode to kernel mode so that CPU can access protected kernel memory."