RSA, Elliptic Curve, DSA, and Elgamal ECES Practice Questions (Page 1)

Questions 1–5

1. 1expert · hard

   A cryptographer is evaluating the security of an Elgamal encryption implementation. They notice that the ephemeral key k is chosen from a small set of values (e.g., 1 to 100). Which of the following attacks is most feasible?

   • AA common modulus attack if the same p is used by multiple users.
   • BA brute-force search over possible k values to recover the plaintext.
   • CA timing attack on the modular exponentiation.
   • DA factorization attack on the modulus p.
   Reveal Solution Discussion Select an answer first
2. 2application · medium

   A developer is implementing elliptic curve point addition for a cryptographic library. Given two distinct points P and Q on the curve, what is the correct formula for the slope λ used to compute P + Q?

   • Aλ = (y2 - y1) / (x2 - x1) mod p
   • Bλ = (3*x1^2 + a) / (2*y1) mod p
   • Cλ = (x2 - x1) / (y2 - y1) mod p
   • Dλ = (y1 + y2) / (x1 + x2) mod p
   Reveal Solution Discussion Select an answer first
4. 3expert · hard

   A company is deploying ECDH for key exchange between a server and many IoT devices. The devices have limited storage and cannot store large certificates. Which of the following is the most appropriate approach to minimize storage while maintaining security?

   • AUse a 256-bit elliptic curve and pre-shared static public keys.
   • BUse a 512-bit elliptic curve and full X.509 certificates.
   • CUse RSA with 2048-bit keys and self-signed certificates.
   • DUse DSA with 1024-bit keys and raw public keys.
   Reveal Solution Discussion Select an answer first
5. 4expert · hard

   A security team is reviewing a DSA implementation and discovers that the random number generator used for the per-message nonce k is flawed and sometimes produces the same k for different messages. Which of the following is the most critical action to take?

   • ARegenerate the domain parameters p, q, and g.
   • BUse the same k for all signatures to make the signatures deterministic.
   • CIncrease the size of the nonce k to 256 bits.
   • DReplace the random number generator with a cryptographically secure one and reissue all keys that signed with the flawed generator.
   Reveal Solution Discussion Select an answer first
6. 5expert · hard

   An organization uses RSA with a 1024-bit modulus. A security auditor warns that the key size is insufficient. Which of the following is the most direct reason why 1024-bit RSA is considered weak today?

   • AThe modulus is shared among multiple users, enabling a common modulus attack.
   • BThe modulus can be factored with sufficient computational resources, breaking the private key.
   • CThe public exponent is too small, allowing a small-exponent attack.
   • DThe totient is even, making the private exponent predictable.
   Reveal Solution Discussion Select an answer first