A security analyst is working on a project that requires the implementation of a stream cipher. Which of the following should the analyst use?

A hash function is a one-way mathematical operation used for data integrity verification or password storage, not for encrypting and decrypting data like a cipher.

Elliptic curve cryptography is a type of asymmetric (public-key) cryptography primarily used for key exchange and digital signatures, not as a stream cipher itself.

Stream ciphers are a category of symmetric-key algorithms that encrypt data one bit or byte at a time using a shared secret key, making symmetric algorithms the appropriate choice for their implementation. This contrasts with block ciphers, which also use symmetric keys but operate on fixed-size blocks of data.

Public key cryptography, also known as asymmetric cryptography, uses separate keys for encryption and decryption and is generally not used for efficient bulk data encryption like stream ciphers.