In theory the Web Crypto API might interact with data encrypted with non-Web Crypto API applications. They may want to preserve compatibility with other APIs.

I was at DefCon this year (for the third straight time). It didn't feel like attendance was 9,000, but that's a really hard number to guess. There are:

- five lecture rooms running at all times (seating, I would estimate, between 1,000 and 3,000 per)
- a couple game rooms (about 150 and 300 in each at any given time)
- a few "villages" (with an average of maybe 150).
- hallways, always people in transit
- the "chillout" area
- the nearby eateries - hotel rooms, because many people don't attend every minute of the conference


So making a good estimate from personal experience is hard.

9,000 is probably a good guess, though, according to the guy who runs the event. According to DarkTangent in the closing cerimony, there were 8,500 official badge passes sold, with lesser quality badges going to those who showed up after the official badge supply was depleted. All 8,500 badges sold out, and I saw quite a few people wearing the backup plastic badges. So 9,000 seems like a good estimate.