Finally managed to get my site verified to my account here! I've had the correct verification code embedded at the bottom of krebsonsecurity.com for months. But apparently, you also need to add something in the "extra fields" area of your Mastodon profile.
As suggested by @jerry, I added the words "website" and then the full URL in the box next to it and hit save. After that, the site was verified!
@briankrebs @jerry Nice. So now we know it is really you. 😄 And we learned that in the #Fediverse, on #Mastodon, verifying your identity is a matter of knowledge and using available technology.
The #DeadBird 
(x_x) makes this feature dependent on your financial status as you have to pay to get verified. This implies that you can kinda "hack" verifying your account with money making #verification useless as a feature to provide #trustworthiness.
I guess this must be one of those fancy ideas of the new #CElo... 
(Sarcasm)
The exact same approach can be taken on Twitter, though.
Yes, Twitter does provide the additional official option, but this out-of-band approach is also available, just as a matter of knowledge and using available technology.
It doesn’t rely on any particular ActivityPub functionality.
@volkris @briankrebs @jerry I see. Thanks for your comment. But what is the paid option intended for? I don't see any use in offering the same feature as paid service and for free.