Not sure about this. "magic" in the sense of file type recognition has no cryptographic/security ambitions. On the other hand, when implementing a network proto

Not sure about this. "magic" in the sense of file type recognition has no cryptographic/security ambitions. On the other hand, when implementing a network protocol, I'd say one needs to be really careful and expect the unexpected at any point (not just in the "magic" phase). What does it buy you (in terms of robustness) to have a fakeable magic number at the start of the stream?