5. Quantum Information

Cryptography And Communication — Quiz

Test your understanding of cryptography and communication with 5 practice questions.

Practice Questions

Question 1

In the context of Quantum Key Distribution (QKD), which of the following best describes a 'man-in-the-middle' attack and how quantum properties fundamentally prevent it?

Question 2

Consider a quantum communication protocol where Alice sends a qubit in the state $|\psi\rangle = \frac{1}{\sqrt{2}}(|0\rangle - i|1\rangle)$. If Bob measures this qubit in the diagonal basis (which measures for $|+\rangle = \frac{1}{\sqrt{2}}(|0\rangle + |1\rangle)$ and $|-\rangle = \frac{1}{\sqrt{2}}(|0\rangle - |1\rangle)$), what is the probability that Bob will measure $|+\rangle$?

Question 3

Which of the following quantum-safe cryptographic algorithms is most suitable for long-term secure storage of data, considering its resistance to quantum attacks and its ability to encrypt large amounts of data efficiently?

Question 4

In the context of quantum-safe cryptography, what is the primary challenge in transitioning from current classical cryptographic systems to quantum-safe ones, beyond just the development of new algorithms?

Question 5

Consider a Quantum Key Distribution (QKD) system using the BB84 protocol. Alice sends a sequence of qubits, and Bob measures them. After sifting, they identify a raw key. If the quantum bit error rate (QBER) is found to be $15\%$ during the error estimation phase, what is the most appropriate next step for Alice and Bob?