I assume he copy pasted the message on his unsecured device.
How many apps had access to that text in his clipboard?
To me this isn't a technical problem with Signal, it's an opsec problem, and that's quite a lot harder to explain to people.
Surely they don't have iCloud on their devices though...
Too deep. The problem is the physical environment, the room in which the machine displays the information. Computer and technological security means nothing if the information is displayed on a screen is in a room where anyone with a camera can snap a pic at any time.
At least in the case of the leak the culprit was the UX, no?
Suppose a user wants the following reasonable features (as was the case here):
1. Messages to one's contacts and groups of contacts should be secure and private from outside eavesdroppers, always.
2. Particular groups should only ever contain a specific subset contacts.
With Signal, the user can easily make them common mistake of attempting to add a contact who already is in the group. But in this case Signal UI autosuggested a new contact, displaying initials for that new contact which are the same initials as a current group member.
Now the user has unwittingly added another member to the group.
Note in the case of the leak that the contact was a bona fide contact-- it's just that the user didn't want that particular contact in that particular group. IIRC Signal has no way to know which contacts are allowed to join certain groups.
I don't know much about DoD security. But I'm going to guess no journalist has ever been invited to access a SCIF because they have the same initials as a Defense Dept. employee.
1. Journalist emailed trusted user seeking comment on something. This email contained the journalist's cell phone number in the signature block.
2. The trusted user forwarded this email to the fool with Signal.
3. The fool's iPhone suggested adding the journalist's cell phone number to the trusted user's contact.
4. The fool accepted this, perhaps blindly.
https://news.ycombinator.com/item?id=43601213
This iPhone feature exists probably to save a few taps when people text you their new phone number.
But it fails to account for the fact that this is not the only reason phone numbers happen to be in texts.
The reason why the policies restrict access to government systems isn’t because anyone thinks that those systems are magically immune to security bugs, but that there are entire teams of actually-qualified professionals monitoring them and proactively securing them. His phone is at risk to, say, a dodgy SMS/MMS message sent by anyone in the world who can get his number, potentially not needing more than a commercial spyware license, but his classified computer on a secure network can’t even receive traffic from them, has locked down configuration, and is monitored so a compromise would be detected a lot faster.
That larger context is what really matters. What they’re doing is like the owner of a bank giving his drunken golf buddy the job of running the business, and the first thing he does is start storing the ledger in his car because it’s more convenient. Even if he’s totally innocent and trying to do a good job, it’s just so much extra risk he’s not prepared to handle for no benefit to anyone else.