I'm wondering about the behaviour of /dev/tty*

How do they works?

Why there are some ttys permissions with crw-rw-rw (generally owned by
root, but some others owned by users), and some others with crw-------
permissions (owned only by users)?

What is the 'c' bit? I've no docs about it.

Are there any security problems about ttys permissions?

Thanks a lot
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