Sarah, an ethical hacker at a San Francisco-based financial firm, is testing the security of...

Blowfish is the only option that matches all the technical characteristics described. In CEH cryptography concepts, symmetric algorithms are commonly distinguished by their structure (block cipher versus stream cipher), block size, and supported key lengths. The question states the algorithm encrypts data in 64-bit blocks and supports a variable key size ranging from 32 bits up to 448 bits, and it was introduced as a replacement for DES. Blowfish fits precisely: it is a symmetric block cipher with a 64-bit block size and a configurable key length from 32 to 448 bits, designed to be fast in software and positioned historically as an alternative to older ciphers such as DES.

The other choices do not align with these identifying properties. RC4 is a stream cipher and does not operate on fixed-size blocks, so it cannot match the 64-bit block requirement. AES is a block cipher but uses a 128-bit block size with fixed key sizes of 128, 192, or 256 bits, not 32 to 448 bits. Twofish, while related historically as a successor-era design, also uses a 128-bit block size and fixed key sizes up to 256 bits, so it does not match either.

From a CEH perspective, the mention of variable key sizes also hints at risk evaluation: shorter keys in any cipher can be brute-forced, so secure deployments require strong key length selection and proper key management. Additionally, Blowfish’s 64-bit block size can be a concern in large-volume encryption scenarios due to block collision risks, which is why modern systems often prefer 128-bit block ciphers for new designs.