CISSP Cryptography 4

Question 1

Which attack exploits the mathematical relationship between related RSA keys when the same plaintext is encrypted with multiple public keys sharing the same exponent?

Accepted Answer

Håstad's broadcast attack

Answer

Håstad's broadcast attack uses the Chinese Remainder Theorem to recover plaintext when the same message is encrypted with multiple RSA public keys using a small exponent like e=3.

Question 2

What is the role of a Key Derivation Function (KDF) in cryptographic systems?

Accepted Answer

To derive cryptographic keys from a master secret or password

Answer

A KDF derives one or more cryptographic keys from a source secret (like a password or master key), often adding salt and iterations to resist brute force.

Question 3

In a hybrid encryption scheme, what is the typical role of asymmetric cryptography?

Accepted Answer

Encrypting the symmetric session key used for data encryption

Answer

Hybrid schemes use fast symmetric encryption for bulk data and asymmetric encryption only to securely transmit the symmetric session key.

Question 4

Which of the following is an example of a stream cipher?

Accepted Answer

RC4

Answer

RC4 is a stream cipher that generates a pseudorandom keystream XORed with plaintext one byte at a time, unlike block ciphers like AES and Blowfish.

Question 5

What cryptographic concept does the Diffie-Hellman problem rely on for its security?

Accepted Answer

The difficulty of computing discrete logarithms

Answer

Diffie-Hellman security relies on the computational difficulty of the discrete logarithm problem: given g^x mod p, finding x is computationally infeasible.

CISSP - Certified Information Systems Security Professional Practice Test

CISSP - Certified Information Systems Security Professional Practice Test

CISSP Cryptography 4