English
Menu

Hardware Security: Advanced Topics and Trends

A task took 10 seconds before mitigations for speculative execution were applied and made 5 million system calls during that time. Assume that the mitigations increase the processing time per system call from 0.4 µs to 0.6 µs and leave the time of everything else unchanged. By what proportion does the total time of the task increase?

  1. Aabout 10%
  2. Babout 30%
  3. Cabout 50%
Show answer and explanation

Answer: A. about 10%

The time spent in system calls is 5 million × 0.4 µs = 2 s before the mitigations and 5 million × 0.6 µs = 3 s after. The increase is 1 s, so the total goes from 10 s to 11 s, an increase of 1 ÷ 10 = 10%. Even though each system call becomes 1.5 times slower (50% more), the effect on the whole is determined by the share of time that part takes (20% here). For this reason, with mitigations such as KPTI, the performance loss is larger for databases and I/O-heavy processing that make many system calls and interrupts.

  • A. Correct. (3 − 2) ÷ 10 = 10%.
  • B. This mistakes the total system-call time after the mitigations (3 s) for the increase.
  • C. This is the increase per system call (0.2 ÷ 0.4), not the increase for the whole task.
Practice this topic Back to topic

Books on Hardware Security: Advanced Topics and Trends Ad

As an Amazon Associate I earn from qualifying purchases.

More Hardware Security: Advanced Topics and Trends questions

  1. Lattice-based post-quantum cryptography repeatedly multiplies polynomials of degree n = 256. If the naive method of multiplying every pair of coefficients needs about n² multiplications and the method using the number-theoretic transform (NTT) needs about n log₂ n, which is closest to the factor by which the NTT reduces the number of multiplications?
  2. The public key of ML-KEM-768 is 1,184 bytes and its ciphertext 1,088 bytes, while the public value of the elliptic-curve key exchange X25519 is 32 bytes. How many times larger than the X25519 public value is the ML-KEM-768 public key?
  3. In ML-KEM decapsulation, the ciphertext is rebuilt from the result of decrypting the received ciphertext with the private key and compared with the received ciphertext. Which is a correct implementation precaution for this part?
  4. You are designing an SoC for an embedded device that will be used for more than 10 years. Which is an appropriate hardware and firmware design to prepare for future cryptographic migration (such as the move to post-quantum cryptography)?
  5. What is the most appropriate benefit of efforts such as OpenTitan and Caliptra that publish the designs of root-of-trust circuits?