Page 1524 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

Chapter 6: Cryptography and Symmetric Key

Algorithms

1. C. To determine the number of keys in a key space, raise 2 to the
power of the number of bits in the key space. In this example, 24 =

16.

2. A. Nonrepudiation prevents the sender of a message from later
denying that they sent it.

3. A. DES uses a 56-bit key. This is considered one of the major
weaknesses of this cryptosystem.

4. B. Transposition ciphers use a variety of techniques to reorder the
characters within a message.

5. A. The Rijndael cipher allows users to select a key length of 128,
192, or 256 bits, depending on the specific security requirements of
the application.

6. A. Nonrepudiation requires the use of a public key cryptosystem to
prevent users from falsely denying that they originated a message.

7. D. Assuming that it is used properly, the onetime pad is the only
known cryptosystem that is not vulnerable to attacks.

8. B. Option B is correct because 16 divided by 3 equals 5, with a

remainder value of 1.

9. B. 3DES simply repeats the use of the DES algorithm three times.
Therefore, it has the same block length as DES: 64 bits.

10. C. Block ciphers operate on message “chunks” rather than on
individual characters or bits. The other ciphers mentioned are all
types of stream ciphers that operate on individual bits or
characters of a message.

11. A. Symmetric key cryptography uses a shared secret key. All

communicating parties utilize the same key for communication in
any direction.