RSA, Elliptic Curve, DSA, and Elgamal ECES Practice Questions (Page 7)

Questions 31–35

1. 31application · medium

   Two parties, Alice and Bob, want to establish a shared secret using ECC. Alice generates a private key a and computes aP, where P is a public base point. Bob generates a private key b and computes bP. They exchange their public values. What does Alice compute to derive the shared secret?

   • Ab(aP)
   • Ba(bP) + b(aP)
   • Ca(bP)
   • DaP + bP
   Reveal Solution Discussion Select an answer first
2. 32application · medium

   A company uses Elgamal encryption for secure messaging. The recipient has a public key (p, g, y) where y = g^x mod p. To send a message m, the sender chooses a random ephemeral key k. Which of the following is the correct pair to send as the ciphertext?

   • ASend (c1 = g^k mod p, c2 = m * y^k mod p)
   • BSend (c1 = m * g^k mod p, c2 = m * y^k mod p)
   • CSend (c1 = g^x mod p, c2 = m * g^k mod p)
   • DSend (c1 = y^k mod p, c2 = m * g^k mod p)
   Reveal Solution Discussion Select an answer first
4. 33foundation · easy

   Which asymmetric algorithm typically provides equivalent security to RSA 3072-bit with a much smaller key size?

   • AECC with a 256-bit key
   • BElgamal with a 256-bit key
   • CRSA with a 256-bit key
   • DDSA with a 256-bit key
   Reveal Solution Discussion Select an answer first
5. 34foundation · easy

   In ECDSA, what is the purpose of the ephemeral key k?

   • ATo encrypt the message before signing
   • BTo generate a unique signature component r, and it must be kept secret and unique for each signature
   • CTo derive the signer's private key from the public key
   • DTo verify the signature by multiplying the public key
   Reveal Solution Discussion Select an answer first
6. 35expert · hard

   A security analyst discovers that two different public keys in the organization's PKI share the same modulus n but have different public exponents e1 and e2. Which of the following attacks is most likely to succeed?

   • AA timing attack, where the attacker measures the decryption time of both keys.
   • BA factorization attack, where the attacker factors n using the two exponents.
   • CA small exponent attack, where the attacker guesses the private exponent because e is small.
   • DA common modulus attack, where an attacker who intercepts a message encrypted to both keys can recover the plaintext.
   Reveal Solution Discussion Select an answer first