> You could represent each octet as an ASCII char reducing it to 4 characters.
Except ASCII is 7-bit, and a number of those are control characters. So you couldn’t, and many that you could would be unreadable. <DEL><NUL><NUL><SOH> for localhost is... not ideal.
That sounds like good laptop sticker material. Could even give readers a hint by using the "there's no place like" saying that I've seen applied to 127.0.0.1 and ::1 already, or prefix some hacking tool. I wonder how many people would get it.
You can type control codes (except for NUL, DEL, CR, LF?) on the Linux console by pressing Ctrl+letter. Might add some security to your disk encryption password, unless you need to enter it from a GUI :)
How do you write DEL, which Ctrl+key is that? I had written this actually as ^H^@^@^A, but realized that ^H may remove characters but is not DEL, so I edited that out of my previous comment.
Yes, I don't know if there is any key combination to type DEL. Ctrl just clears bit 6. ^S and ^Q are also problematic because of XON/XOFF. I did use ^G (BEEP!) in a password once.
edit ^H is also swallowed by the line editor of course.