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Forcing iMessage to open will immediately result in MITM iMessage proxies that users can use to store iMessages that are meant to auto-delete, so that they can violate the wishes of the other party. These do not exist today because Apple binds iMessage to your hardware and bans your entire device when anyone is found to be operating such a service, either for themselves or others.

Do you want open source clients that can be altered to ignore all privacy criteria — or do you want closed-source clients that make a good faith effort to adhere to auto-deletion protocols?

Pick one. There is no middle ground.

iMessage doesn't have any kind of auto deleted messages - it's a feature that messages are persistent across all your devices.

Incorrect. Audio messages are deleted two minutes after playback by default.

Which is a receiver-side setting and can be set to one year. Your point is moot.

For me, the two choices in settings are "after two minutes" and "never", nothing in between. As you said, this is not a security setting, it's a storage space-saving setting.

This is unrelated to the current discussion and not meant to contradict your "Your point is moot", but instead just as a hopefully useful anecdote: In my experience, this requires the sender to choose 'Keep' too. I have been bitten several times by me sending an audio message to my wife because I was in a situation in which typing was complicated for me (outdoors, plenty of sunshine, I don't have the best eyesight), only to find that she never even got to see it because it got self-deleted after a few minutes.

My conjecture from looking at how this has worked for me is that the sender must choose 'Keep' so that the audio message stays on the receiver's phone until listened, and the recipient must choose 'Keep' so that the audio message stays on their phone after listening.

I, of course, have no proof of this other than my own experience on devices a few years old (iphones 5 and 6).

I also had some odd occurrences like this, and I simply stopped using voice messages over iMessage. It hasn't really penetrated the local phone culture so to speak, so it isn't a problem. Those that I do use it with happen to be on WhatsApp, which retains messages forever or something.

That's a client side feature meant to save disk space.

You can violate the wishes of the other party by taking a screenshot or, in the extreme, a photo of the screen. You're only preventing the very lazy/unmotivated from retaining messages.

Correct, screenshots are a viable attack against both closed and open source platforms. Preventing casual retention is the best you can hope for, and is a worthy goal regardless that it does not result in the perfection of a Faraday cage’d clean room

So, your threat model includes MITM servers, but not cameras? It seems a little silly to worry about the MITM problem when you can simply snap a photo already.

If you have to get into a legal battle with someone about misuse of information, it's much better that you are able to focus on the sender and the recipient of the information as potential sources for that information instead of also having to go after every potential network hop as well.

They are both valid threat models, but ones which for me have different meanings.

Screenshotting or photographing the screen of a device owned my my intended message recipient is a reasonably small problem to me. If my recipient wants to expose a message I've sent them, they're going to be able to do that. I never expected any more privacy for that message than I'd have accepted based on my trust in that person.

MITM servers are a whole other thing. Large scale surveillance of all users of a specific server, "full take" collection and searchable databases of messages available effectively forever to unknown current and future opponents?

Different threats. Yeah, I'm happy enough to accept the risk of cameras in the hands of my correspondents. Way happier than I'd be with MITMable servers (or services that can add "ghost users" as the UK seems to be proposing).

I might be missing something, but how would large scale surveillance with searchable databases be possible with e2e encryption? They could save the messages, but they would still be encrypted.

Actually apples approach results in a MUCH lower level of retention than other providers even if someone can screenshot all conversations

Just like with Snapchat, Auto-delete is a fantasy and is not worth sacrificing security or privacy for.

> The sub-packets that the author mentions were primarily used for dealing with forwarded chains of encrypted email messages where each previous message had it's own embedded mime-encoded encrypted/signed messages and attachments.

If you ("you" here being the PGP team) knew going into the design that the use-case of ASCII-armored-binary (.asc) documents is specifically transmitting them in a MIME envelope... then, instead of making .asc into its own hierarchical container format, why didn't you just use MIME, which is already a hierarchical document container format?

I.e., if you're holding some plaintext and some ASCII-armored-binary ciphertext, why not just make those into the "parts" of a mime/multipart container, and send that as the email?

Then all the work of decoding—or encoding—this document hierarchy would be the job of the email client. The SMIME plugin would only have to know how to parse or generate the leaf-node documents that go into the MIME envelope (and require of the email client an API for retrieving MIME parts that the SMIME parts make reference to.)

And you'd also get the advantage of email clients showing "useful" default representations for PGPed messages, when the SMIME extension isn't installed.

• Message signature parts would just be dropped by clients that don't recognize them. (Which is fine; by not having SMIME installed, you're opting out of validating the message, so you don't need to know that it was signed.)

• Encrypted parts would also be dropped, enabling you to send an "explanation" part as a plaintext of the same MIME type to the "inner" type of the encrypted part, explaining that the content of the message is encrypted.

I guess this wouldn't have worked with mailing lists, and other things completely ignorant of MIME itself? But it would have been fine for pretty much all regular use of SMIME.

Have you looked at DIME?

https://darkmail.info

I can't see that happening: There are multiple other messaging apps that are clearly successful and popular on iOS and macOS, and neither iOS nor macOS are the majority OS.

Until a better solution is brought forward, my team implemented a PGP packet library to make everyone's lives a little bit easier: https://github.com/summitto/pgp-packet-library

Using our library you can generate PGP keys using any key derivation mechanism for a large variety of key types! When using it right, this will greatly improve how you can generate and back up your keys!