Which technology threatens widely used public-key systems such as RSA and ECC?

• A. Classical computers with higher processing power
• B. Quantum computers
• C. Random number generators
• D. Symmetric ciphers

Answer: (B)

Quantum computing can break RSA and ECC by running Shor's algorithm, which is why this topic is about the vulnerability of public-key cryptography to quantum attacks. Public-key systems rely on hard math: factoring large numbers for RSA and the elliptic-curve discrete logarithm problem for ECC. A capable quantum computer can solve these problems in polynomial time, allowing it to derive a private key from a public key and decrypt or forge messages. Classical computers, even very powerful ones, cannot do this feasibly with today’s key sizes, which is why they don’t pose the same immediate risk. While random-number generation and symmetric ciphers have their own considerations, the direct threat to widely used public-key schemes comes from quantum-enabled algorithms, motivating the move toward quantum-resistant algorithms.