What is RSA?

• A. A symmetric encryption algorithm.
• B. A hashing algorithm.
• C. Algorithm for public-key encryption described in 1977 by Ron Rivest, Adi Shamir, and Len Adleman.
• D. A password hashing scheme.

Answer: (C)

RSA is a public-key cryptosystem described in 1977 by Rivest, Shamir, and Adleman. It uses a pair of keys: a public key that can be shared openly for encryption or verifying a signature, and a private key that stays secret for decryption or creating a signature. The security rests on the difficulty of factoring the product of two large primes. In RSA, you generate two large primes, compute n = p × q, choose a public exponent e that is coprime with φ(n), and determine the private exponent d as the modular inverse of e mod φ(n). Encryption works by raising the message to the power e modulo n, and decryption uses d. RSA is widely used for secure key exchange and digital signatures, but it’s slower than symmetric algorithms, so it’s typically used to protect a symmetric key rather than large data directly. The other options describe symmetric encryption, hashing, or password hashing, which are different concepts.