Encrypt given data using cast5-cfb cipher algo. CAST5 in CFB (Cipher Feedback) mode, a stream cipher mode that encrypts small blocks of data. CAST5 is the 128-bit variant of the CAST family, designed for higher security than earlier CAST versions and supporting multiple modes like CFB. CAST5-CFB is secure but has been overshadowed by stronger, more modern encryption algorithms. Our encryption process prepends the IV string used during the encryption process in the encrypted data so that it can be used during decryption.