This letter of authorization is also the first instance of where learning about how the Internet actually works gets a little weird. That letter is literally all it took for me to take control of a sub-block of someone else's public address space and get it routed to my network instead of theirs. Some of my network peers later asked for me to provide this LoA when we were setting up my network links, but that means I just sent them a PDF scan of a letter with my friend's signature on it. And I mean an actual signature; not some kind of fancy cryptographic signature, but literally a blue scribble on a piece of paper.
I can't wait for the Hackernews post where someone social-engineers their way into controlling an IP block and posts about it on twitter.
With one of my upstreams (a large Tier 1 you've heard of), I can announce any prefix I want. I just have to add a "route" entry to the routing registry database and wait a day or two for them to update their filters on my BGP session.
It's easily doable (I do it occasionally so I can announce customers' prefixes for them) but I'd "get caught" if I was announcing prefixes I shouldn't be.
At the 26C3 congress in 2009 there was a talk[1] about just that happening: companies that were looking for abandoned ASNs/IPv4 allocations and then using shady tricks (creating similarly-named companies, ...) to get them in their possession.
I can't wait for the Hackernews post where someone social-engineers their way into controlling an IP block and posts about it on twitter.