The most popular public key encryption cipher is ________.

• A. AES
• B. DES
• C. RSA
• D. ECC

Answer: (C)

Public-key cryptography uses a pair of keys: a public key for encryption (or verification) and a private key for decryption (or signing). RSA has been the most widely deployed public-key scheme for encryption and key exchange for many years, with broad support across protocols and systems (like TLS and various email standards). Its long-standing interoperability and widespread implementation make it the go-to public-key cipher in practice.

The other options don’t fit as the popular public-key cipher in this sense: DES and AES are symmetric ciphers, using the same key for both directions, not public-key systems. Elliptic Curve Cryptography is also public-key and increasingly common, but RSA remains the most widely adopted in many existing deployments, which is why it’s considered the most popular choice.