I've upgraded to iOS 9 GM and El Capitan GM, and I saw some new items show up in my iCloud Keychain, titled:

    PCS Backup
    PCS CloudKit
    PCS Escrow
    PCS FDE
    PCS iCloudDrive
    PCS iMessage
    PCS Maildrop
    PCS MasterKey
    PCS News
    PCS Notes
    PCS Photos

(They also have what looks like a base64 string in there, but I'm excluding that just in case it might be secret)

Just a guess, but between this and the fact that iCloud Backups were broken during the iOS 9 beta period, it seems like they might be encrypting backups now, as well.

The problem with encrypting backups is what do they use as the encryption key? You have to have some route back to the users password, as that's what they'll be using to restore. That leaves it vulnerable to a LE password reset even if the backup is encrypted.

iCloud Keychain solves this problem, if you use a complex passphrase:

http://www.slideshare.net/alexeytroshichev/icloud-keychain-3...

The key could be added to the appleid on the server, without telling the phone about it. Others sending messages to you would then also encrypt with the new backdoor key. Likewise, you don't get notifications about your friends' keys updating (in fact there's not even any UI to show the current keys for a contact), so your phone would start encrypting messages to the recipient's additional backdoored key silently too. :(

> Also, I thought the consensus was that Apple was 'backdooring' iMessage by giving LE access to iCloud backups which include iMessage, not compromising iMessage directly?

Can you please expand on this? How would access to iCloud backup not compromise iMessage?

The backups store messages as plaintext within the [encrypted?] backup. This compromises the messages themselves, but not the iMessage protocol nor systems.

iCloud backups are not encrypted, and they include iMessage conversations. So the backups don't compromise the iMessage "service" or "application," but simply provide access to messages sent and received before the backup was made.

>Also, I thought the consensus was that Apple was 'backdooring' iMessage by giving LE access to iCloud backups which include iMessage, not compromising iMessage directly?

Consensus? First I've heard of this being a consensus. I've heard people say if Apple is backdooring, this is the way they'd do it, but no consensus on this actually happening. Care to go into this a bit more?

Consensus may have been the wrong word to use, but I've heard the same as you, that backups are a weak point in iMessage security, and a very plausible way for LE to get access.

is it required to have an iCloud backup when using iOS? Or is it something that can be opted out of? I'm just curious.

Just have more than 5 GB of data and you can't backup to iCloud without paying monthly.

Photos are not included, Apps aren't (only their data), I'm not sure about music. It's gonna be hard to exceed the 5GB this way

Photos may be included.

"Here’s what iCloud backs up: Photos and videos on your iOS devices, unless you turn on iCloud Photo Library on your iOS device (iOS 8.1 or later)."

https://support.apple.com/kb/PH12519?locale=en_US

The photos hit the same 5 GB limit, so it's not like excluding or including them really changes anything. Photos are the #1 reason people hit the backup limit.

Thanks, didn't know that (I use iCloud Photo Library), but IIRC you can disable stuff from backing up, even photos

I currently use 18 GB with only a single iPhone. 14.6 GB of this is my iCloud Photo Library.

You can opt out, but I think it will be the default.

Not required. You can choose between iCloud backup, iTunes backup (even encrypt if you want) and no backup at all. iCloud is the most convenient though