Thanks for bringing Cyberdust up — called Dust now, right? Let me know if I am wrong.
I am leaving apart the encryption protocol and just looking at metadata for now. As mentioned in my article:
using end-to-end encryption does not prevent messaging services from collecting metadata.
And I would add that deleting messages from phones does not prevent a messaging service from collecting metadata either.
3. INFORMATION WE COLLECT
We collect information you provide directly to us when you create your account. This may include your username, password, email address, phone number, age and any other information you choose to provide.
With your authorization, we may also have access to your contact list(s) (e.g. so you may find friends) or photo roll(s) (e.g., so you may send photos).
And it goes on:
We may collect usage Information, including time, date, sender and recipient of message, the number of messages sent and received, and the amount of time you spend on Dust. We may collect information about your use of our websites, including your browser type and language, access times, pages viewed, your IP address and the website you visited before navigating to our websites.
So again, it is not so much about the encryption part or the “disappearing messages” feature but more about the metadata these applications collect.