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 network with a block size of 64 bits for encryption, which includes large 8 32-bit S-boxes (S1, S2, S3, S4) based on bent functions, modular addition and subtraction, key-dependent rotation, and XOR operations. This cipher also uses a masking key (Km1) and a rotation key (Kr1) for performing its functions.
What is the algorithm employed by Harper to secure the email messages?

A. CAST-128
B. AES
C. GOST block cipher
D. DES