Harper, a software engineer, is developing an email application. To ensure the confidentiality of email messages, Harper uses a symmetric-key block cipher having a classical 12- or 16-round Feistel ne

CAST-128 is a symmetric-key block cipher that employs a 12- or 16-round Feistel network with a 64-bit block size. Its design incorporates large 8x32-bit S-boxes derived from bent functions, along with modular addition/subtraction, key-dependent rotation, and XOR operations, utilizing both masking (Km1) and rotation (Kr1) keys in its round function, matching all details provided in the question.

AES uses a 128-bit block size and is a substitution-permutation network, not a Feistel cipher, which fundamentally contradicts the description of the algorithm.

While GOST block cipher uses a 64-bit block size and a Feistel network, it uses 4x4-bit S-boxes, not the 8x32-bit S-boxes based on bent functions described in the question.

DES uses a 64-bit block size and a Feistel network, but it employs 6x4-bit S-boxes and does not feature the specific 8x32-bit S-boxes based on bent functions or the explicit masking and rotation keys (Km1, Kr1) as described.