47. Which of the following should not exist outside the cryptographic boundary of the crypto-module?
a. Shared secrets and intermediate results
b. Domain parameters and initialization vectors
c. Random number generator seeds and nonce
d. Nonce and salt
47. a. Shared secrets are generated during a key establishment process. Intermediate results of cryptographic operations are generated using secret information. Therefore, both shared secrets and intermediate results should not exist outside the cryptographic boundary of the crypto-module due to their sensitivity and criticality. The other three choices either do not exist outside the cryptographic boundary or they are less sensitive and critical.
48. What describes the crypto-period of a symmetric key?
a. Originator usage period plus retention period
b. Retention period minus recipient usage period
c. Originator usage period plus recipient usage period
d. Recipient usage period minus originator usage period
48. c. The crypto-period of a symmetric key is the period of time from the beginning of the originator usage period to the end of the recipient usage period.
49. Which of the following should be destroyed immediately after use?
a. Random number generator seeds and intermediate results
b. Nonce and shared secrets
c. Domain parameters and initialization vectors
d. Shared secrets and intermediate results
49. a. Both random number generator (RNG) seeds and intermediate results should be destroyed after use due to their sensitivity. Domain parameters remain in effect until changed. Shared secrets and initialization vectors should be destroyed as soon as they are no longer needed. A nonce should not be retained longer than needed for cryptographic processing.
50. Which of the following provides the weakest cryptographic algorithms?
1. A 160-bit ECDSA key is used to establish a 128-bit AES key.
2. A 256-bit ECDSA key is used to establish a 128-bit AES key.
3. A 256-bit SHA key is used with a 1024-bit RSA key.
4. A 256-bit SHA key is used with a 2048-bit RSA key.
a. 1 only
b. 1 and 3
c. 2 and 3
d. 2 and 4
50. b. The strength of cryptographic protection is determined by the weakest algorithm and the key size used. This is explained as follows:
A 160-bit ECDSA and 128-bit AES provide 80 bits of security.
A 256-bit ECDSA and 128-bit AES provide 128 bits of security.
A 256-bit SHA and 1024-bit RSA provide 80 bits of security.
A 256-bit SHA and 2048-bit RSA provide 112 bits of security.
Therefore, 80 bits of security is weaker than 112 bits and 128 bits of security.
51. How is a cryptographic algorithm’s security life defined?
a. Security life of data plus retention data life
b. Originator usage period plus the security life of the data
c. Recipient usage period plus the retention period
d. Crypto-period plus security life of the data
51. b. A cryptographic algorithm’s originator usage period is the period of time that a cryptographic algorithm and the key size are used to apply cryptographic protection. When the security life of the data is taken into account, cryptographic protection should not be applied to data using a given algorithm and key size if the security life of the data extends beyond the end of the algorithm security lifetime. Hence, the algorithm security life is the algorithm originator usage period plus the security life of the data.
52. Which of the following should not be distributed?
a. Shared secrets
b. Domain parameters
c. Initialization vectors
d. Random number generator seeds
52. a. A shared secret is a secret value that has been computed using a key agreement scheme and is used as input to a key derivation function. Hence, shared secrets should not be distributed while the other three choices can be safely distributed most of the time. Because the initialization vectors are often stored with the data that they protect, a determined attacker (not a normal attacker) could take advantage of them for hacking.
53. Which of the following need not be backed up?
a. Private key transport key
b. Public key transport key
c. Public authentication
d. Private signature key
53. d. The private signature key need not be backed up because nonrepudiation would be in question. This is because proof-of-origin and proof-of-delivery are needed for a successful nonrepudiation using private signature key by the originator (i.e., the signatory). Therefore, the private signature key should be protected in a safe and secure location. The other three choices can be backed up without any question.
54. What is the major advantage of a checksum program?
a. Adds more bytes to programs
b. Verifies integrity of files
c. Increases boot-up time
d. Misleads a program recompilation
54. b. A checksum is a program that forms a cryptographic checksum of files in a computer system to allow their integrity to be checked at will. However, the checksum program adds overhead to the system in terms of adding more bytes to each program and increases boot-up time by several minutes. Any attempt to recompile a program will be flagged as a “virus type” activity (when it is not) and will be stopped. It misleads a program recompilation process.
55. Which of the following need not be archived?
a. Private signature key
b. Symmetric authentication key
c. Public authentication key
d. Symmetric master key
55. a. An archive for keying material (i.e., keys and initialization vectors) should provide both integrity and access control. When archived, keying material should be archived prior to the end of the crypto-period of the key. When no longer required, the keying material should be destroyed. Private signature key need not be archived because it is private but should be protected in a safe and secure location.
Both symmetric and public authentication keys should be archived until no longer required to authenticate the data. A symmetric master key should be archived until no longer needed to derive other keys.
56. What is a simpler alternative to a digital signature?