The most popular public key cipher is RSA.

• A. True
• B. False
• C. Not sure
• D. Not Applicable

Answer: (A)

RSA has long been the most widely deployed public-key cipher because of its straightforward math, strong security basis, and broad early standardization. It’s simple to use: encrypt with a public key and decrypt with the private key, and its security is tied to the difficulty of factoring large integers, a well-studied problem. Because of that, RSA became the default choice in many protocols and libraries (TLS, email, digital signatures, and S/MIME, among others), so it ended up being the most common public-key cryptosystem in real-world deployments.

Elliptic-curve cryptography is popular for offering comparable security with much smaller key sizes, which improves efficiency, and it’s increasingly used in modern systems. Still, in terms of overall usage and historical dominance, RSA remains the most common public-key cipher, which is why the statement is considered true.