Chapter 5 – Cryptography
TRUE/FALSE
1. Encrypted files can be transmitted in both electronic form and as written messages.
2. A hash value is a variable-length string of symbols and numbers representing the original input’s
contents.
3. The standardization of cryptographic protocols discourages attackers from trying to break them.
4. Because IPsec Security Associations are bidirectional, only one need be established between two
parties.
5. In a passive attack, cryptanalysts eavesdrop on transmissions but don’t interact with parties
exchanging information.
MULTIPLE CHOICE
1. Which of the following is NOT a critical goal of information security?
a.
confidentiality
c.
authentication
b.
scalability
d.
nonrepudiation
2. Which of the following is true about cryptographic primitives?
a.
each performs several tasks
c.
primitives are usually not the source of
security failures
b.
a single primitive makes up an entire
cryptographic protocol
d.
a primitive that provides confidentiality
usually also provides authentication
3. Which type of function is used in cryptography?
a.
Not AND
c.
NOR
b.
permutation
d.
X-box
4. Which of the following best describes a one-way function?
a.
a bit string that prevents generation of the
same ciphertext
c.
generates secret keys from a secret value
b.
random bits used as input for key
derivation functions
d.
easy to compute but difficult and time
consuming to reverse
5. Which of the following is true about PRNGs?
a.
they are not completely random
c.
the shorter the state, the longer the period
b.
their state is measured in bytes
d.
they can never produce the same value
6. Which of the following is commonly used for verifying message integrity?
a.
registration authority
c.
pseudorandom number generator
b.
CRL
d.
hashing function
7. Which of the following is true about encryption algorithms?
a.
their strength is tied to their key length
c.
block ciphers encrypt one bit at a time
b.
not vulnerable to brute force attacks
d.
asymmetric algorithms use a single key
8. Which of the following is described as a 64-bit block cipher composed of a 16-round Feistel network
and key-dependent S-box functions?
a.
Twofish
c.
Blowfish
b.
RC4
d.
Rijndael
9. Which of the following makes a single pass on data and generates a 128-bit hash value displayed as a
32-character hexadecimal number and is used in VPNs?
a.
RSA
c.
RC4
b.
Message Digest 5
d.
Twofish
10. Which of the following is true about Message Authentication Code.
a.
it uses asymmetric encryption
c.
is uses PKI and certificates
b.
the key is sent to the receiver securely
d.
it uses a private and public key
11. Which of the following is the first step in the digital signature process where Mike sends a message to
Sophie?
a.
a message digest of Mike’s message is
calculated using a hashing algorithm
c.
Sophie encrypts Mike’s message with
Mike’s public key
b.
Sophie compares the message digest she
calculated to Mikes’s message
d.
the message digest is encrypted by Mike’s
private key
12. What is the most likely weak link when using asymmetric encryption for verifying message integrity
and nonrepudiation?
a.
the use of the sender’s private key
c.
the source of the public keys
b.
the hashing algorithm used to generate a
message digest
d.
the integrity of the private keys
13. Which of the following is true about asymmetric cryptography?
a.
the private key can be used to encrypt and
decrypt a message
c.
a single key is used and is transferred
using a key management system
b.
a shared key is used to encrypt all
messages and the private key decrypts
them
d.
the public key is used to encrypt a
message sent to the private key owner
14. Which of the following best describes a CRL?
a.
a published listing of invalid certificates
c.
a file that contains information about the
user and public key
b.
serve as a front end to users for revoking
certificates
d.
keeps track of issued credentials and
manages revocation of certificates
15. Which of the following is a current standard for PKI that specifies a strict hierarchical system for CAs
issuing certificates?
a.
PKCS #2
c.
DES
b.
X.509
d.
SHA-1
16. What is a downside to using Triple DES?
a.
uses only a 56-bit key
c.
using three keys decreases security
b.
goes through three rounds of encryption
d.
requires more processing time
17. Which of the following was developed as a way of enabling Web servers and browsers to exchange
encrypted information and uses a hashed message authentication code to increase security?
a.
SSH
c.
TLS
b.
SSL
d.
IPsec
18. At which layer of the OSI model does IPsec work?
a.
Two
c.
Four
b.
Three
d.
Six
19. Which component of IPsec enables computers to exchange keys to make an SA?
a.
IKE
c.
Oakley
b.
ISAKMP
d.
IPsec driver
20. Which of the following is a type of cryptanalysis that applies primarily to block ciphers but can also be
used against stream ciphers and hashing functions and works by examining how differences in input
affect the output?
a.
integral
c.
related key
b.
differential
d.
XSL
COMPLETION
1. ______________________ is achieved when neither party can plausibly deny its participation in
message exchanges.
2. A ______________ value is a fixed-size string representing the original input’s contents.
3. A ________________ occurs when computing the MD5 algorithm with two different initialization
vectors produces the same hash value.
4. Digital ____________________ security vulnerabilities are mostly associated with the IT
infrastructure required to support interoperability.
5. ______________ cryptanalysis is applicable to block ciphers that use a substitution-permutation
network including Rijndael, Twofish, and IDEA.
MATCHING
a.
AES
f.
XOR function
b.
block cipher
g.
IPsec
c.
ciphertext
h.
key management
d.
cryptanalysis
i.
plaintext
e.
DES
j.
stream cipher
1. the study of breaking encryption methods
2. unreadable text, programs that do not execute, and graphics you cannot view
3. A set of standard procedures that the Internet Engineering Task Force (IETF) developed for enabling
secure communication on the Internet
4. a type of encryption algorithm that encrypts one bit at a time
5. the current U.S. government standard for cryptographic protocols
6. readable text, programs that execute, and graphics you can view
7. an older protocol composed of a 16-round Feistel network with XOR functions, permutation functions,
64 S-box functions, and fixed key schedules
8. a way to prevent keys from being discovered and used to decipher encrypted messages
9. a cryptographic primitive based on binary bit logic and used as a linear mixing function, combining
values for use in further computations
10. a type of encryption algorithm that encrypts groups of cleartext characters
SHORT ANSWER
1. Describe the exclusive OR function.
2. What is a Feistel network and what is its purpose?
3. What does a key derivation do?
4. What is a hash value and how does it verify message integrity?
5. How does the key size affect the strength of an encryption algorithm?
6. Compare and contrast block cipher with stream cipher.
7. How does an asymmetric algorithm differ from a symmetric algorithm?
8. What three conditions must be true to make a hashing algorithm secure?
9. What is a MAC tag and how does it work?
10. What is a digital signature and for what purpose is one used?