Encrypt given data using cast5-ofb cipher algo. CAST5 in OFB (Output Feedback) mode, which converts the block cipher into a stream cipher using a feedback loop. CAST5, like other CAST variants, was designed in the 1990s and supports OFB mode for better performance than ECB. CAST5-OFB is secure, though it is less commonly used than more popular stream ciphers like ChaCha20. Our encryption process prepends the IV string used during the encryption process in the encrypted data so that it can be used during decryption.