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Hardware Security: Advanced Topics and Trends

A fault injection attempt succeeds with a probability of 0.1% each time, and the results of attempts are independent. Which is closest to the probability of at least one success in 1,000 attempts?

  1. Aabout 0.1%
  2. Babout 63%
  3. C100%
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Answer: B. about 63%

The probability of no success at all is (1 − 0.001)¹⁰⁰⁰ ≈ e⁻¹ ≈ 0.368, so the probability of at least one success is 1 − 0.368 ≈ 0.632, about 63%. Even with a low success rate per attempt, an attack that can be tried thousands of times automatically is quite likely to succeed. Countermeasures therefore combine lowering the per-attempt success rate with mechanisms such as erasing keys after a few detected anomalies or counting and limiting attempts. Simply computing 0.1% × 1,000 = 100% is an error that double-counts cases with more than one success.

  • A. This is the probability for a single attempt.
  • B. Correct. 1 − 0.999¹⁰⁰⁰ ≈ 63%.
  • C. This simply multiplies 0.1% × 1,000, which is wrong as a probability calculation.
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More Hardware Security: Advanced Topics and Trends questions

  1. Suppose a firmware signature check is skipped by a single fault injection attempt with a probability of 1/1,000. The same check is now done in two places, so that the attack succeeds only if both are skipped. If one attempt can target both places at once and each is skipped independently with probability 1/1,000, what is the expected number of attempts until the attack succeeds?
  2. Among the TEEs used in confidential computing, which correctly describes the difference between VM-based TEEs that protect a whole virtual machine (such as AMD SEV-SNP and Intel TDX) and enclave-based TEEs that protect part of an application (such as Intel SGX)?
  3. Why was encrypting virtual machine memory alone considered insufficient in VM-based TEEs, so that mechanisms protecting memory integrity were added, as in AMD SEV-SNP?
  4. Consider a circuit that adds tamper detection and replay protection to memory encryption. For every 64-byte cache line, an 8-byte MAC (a code for detecting tampering) and an 8-byte counter that increases on every write are stored in main memory. Ignoring the tree that protects the counters, what is the extra storage needed as a proportion of the amount of data protected?
  5. In confidential computing, a user's verification server (the verifier) checks the attestation report received from a VM-based TEE before handing over the key that decrypts the data. Which is the most appropriate set of things for the verifier to check?