Which stream cipher is a variant of the Salsa20 cipher, designed to be fast, secure,...

The correct answer is C — ChaCha.

According to WGU Cybersecurity Architecture and Engineering (KFO1 / D488) materials, ChaCha is a stream cipher developed as a variant of Salsa20. It offers enhanced security, improved performance, and resistance to cryptographic attacks. It is often combined with Poly1305 forauthenticated encryption, commonly used in modern secure communications.

CTR (A) and CBC (B) are block cipher modes, not stream ciphers. ECB (D) is a block cipher mode and is insecure due to its lack of diffusion properties.

Reference Extract from Study Guide:

"ChaCha is a modern stream cipher, evolved from Salsa20, designed for speed and security, and often used alongside Poly1305 for authenticated encryption."

— WGU Cybersecurity Architecture and Engineering (KFO1 / D488), Encryption Technologies

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