[zeveb]

> Yes, it's supposed to be a hash of the user's identifier.

Which is why it's a privacy issue: given someone's public identifier, I can see what his key is and how it changes over time. I can see if he has a key, which is interesting information. As I noted, I can probably monitor traffic to find messages encrypted by or to his key.

Heck, I can pregenerate many potentially-valid identifiers (e.g. [0-9az]+@[a-z][0-9az]+\.(com|net|org|edu) and look for them in the public blockchain, and use that to confirm whether the accounts are valid or not (this could be used to see if an email address is valid without ever sending email to it). I could use this to verify addresses before sending out spam or malware.

If I can see two identifiers who communicate with one another, I could use this to, say, malware purportedly from one to the other via unsigned email, who is likely to trust it because it appears to be from someone he knows.

You see the issues, I hope. This kind of thing really is tough.