19 ms·

If you lose your device and buy a new one and restore your device with a back up, all your messages will be returned. There’s no way to accomplish this without

If you lose your device and buy a new one and restore your device with a back up, all your messages will be returned. There’s no way to accomplish this without having the private key in the backup. EDIT: When I say there is no way to accomplish this, I’m talking specifically about the process that exists today where the user doesn’t have to remember a password other than their iCloud password (which today, can also be reset).

ajross 7y ago
> There’s no way to accomplish this without having the private key in the backup. Uh, no. There's no way to accomplish that without some kind of user-managed escrow (even a pass phrase would be fine). It's maybe not the seamless experience Apple wants to offer, but it's certainly not impossible. Frankly the kind of dummyproof restore being offered is fundamentally incompatible with private backups.
yjftsjthsd-h 7y ago
I would think that you could, however, encrypt that private key with a user-controlled password. (Granted, this should be optional and have big red warnings about being unable to recover without the password)
- jedieaston 7y ago
  That’s exactly what they do for iCloud Keychain and Health data right now, so I don’t understand why they don’t do it for messages by default.
snowwrestler 7y ago
Maybe we're talking about different private keys? To clarify, here's how I think it works: 1) To send you a new iMessage, someone else's iPhone Z encrypts it with your public key and sends it through the iMessage network. Apple can't read this message since they don't have your iMessage private key, which is only on your device. 2) Your iPhone A receives the encrypted iMessages and decrypts them with your iMessage private key on your device. 3) iPhone A stores the decrypted iMessage content in its filesystem, which is encrypted locally with the device private key (derived from your device passcode). 4) Time to backup... iPhone A decrypts its filesystem with your device private key, and sends filesystem contents as plaintext, through an encrypted tunnel, to an iCloud backup server, which encrypts the backup locally with an iCloud server private key, and stores it. 5) You get a new iPhone, let's call it iPhone B. iPhone B asks iCloud for a restore. The iCloud server locally decrypts the backup, and sends it to iPhone B as plaintext through an encrypted tunnel. iPhone B receives the backup as plaintext and stores it locally, encrypting it locally with the device private key. 6) iPhone B iMessage client loads the plaintext old iMessages into the Messages client for you to read. At no point in this process would Apple have or store your iMessage private key or your device private key.
- nemothekid 7y ago
  You are right; Apple isn't storing your private key, they simply have access to an unencrypted dump of your iPhone at the time of iCloud backup creation. My comment implies that once you take a backup, Apple would have the ability to read all your future messages as well.
- dwaite 7y ago
  The encryption is a bit complex on the iPhone, because keys are typically held by the secure enclave which enforces policy on use. These keys are both used to encrypt the base filesystem, and can be applied by policy against individual files. Example policies from the Secure Enclave would be that a private key is available on first unlock, only while unlocked, only while a PIN is set, and/or whether the key should be shared with other trusted devices. The base filesystem is encrypted with a key released on boot, while individual files can be encrypted with some set of these policies. I believe this can be done either on individual files in an app's data, or as an entitlement to apply by default to the entire app. https://developer.apple.com/documentation/bundleresources/entitlements/com_apple_developer_default-data-protection https://developer.apple.com/documentation/bundleresources/en... My understanding is that files set with a policy that they are only available while the device is unlocked will still be backed up in the locally encrypted form. So, assuming Signal/WhatsApp/etc set a single flag their data is stored encrypted in iCloud. Further, per your list I suspect that the backup data is sent to/from iCloud already encrypted by a secret - but that secret is shared with iCloud for recovery and shared further on official government request. The goal there is to limit the amount of unencrypted user data sent to third party servers (in this case in the US I believe Azure-hosted storage for backups). The keys are separately stored on Apple-controlled servers in non-China countries. In China, I believe they were required by law to have the key storage instead hosted by a Chinese data center.
madeofpalk 7y ago
> all your messages will be returned. Your messages are returned via the backup, not via the "iMessage servers". Once the messages are at rest on your device, they're no longer encrypted using your "iMessage private key".

ajross 7y ago

> There’s no way to accomplish this without having the private key in the backup. Uh, no. There's no way to accomplish that without some kind of user-managed escrow (even a pass phrase would be fine). It's maybe not the seamless experience Apple wants to offer, but it's certainly not impossible. Frankly the kind of dummyproof restore being offered is fundamentally incompatible with private backups.

yjftsjthsd-h 7y ago

I would think that you could, however, encrypt that private key with a user-controlled password. (Granted, this should be optional and have big red warnings about being unable to recover without the password)

jedieaston 7y ago
That’s exactly what they do for iCloud Keychain and Health data right now, so I don’t understand why they don’t do it for messages by default.

snowwrestler 7y ago

Maybe we're talking about different private keys? To clarify, here's how I think it works: 1) To send you a new iMessage, someone else's iPhone Z encrypts it with your public key and sends it through the iMessage network. Apple can't read this message since they don't have your iMessage private key, which is only on your device. 2) Your iPhone A receives the encrypted iMessages and decrypts them with your iMessage private key on your device. 3) iPhone A stores the decrypted iMessage content in its filesystem, which is encrypted locally with the device private key (derived from your device passcode). 4) Time to backup... iPhone A decrypts its filesystem with your device private key, and sends filesystem contents as plaintext, through an encrypted tunnel, to an iCloud backup server, which encrypts the backup locally with an iCloud server private key, and stores it. 5) You get a new iPhone, let's call it iPhone B. iPhone B asks iCloud for a restore. The iCloud server locally decrypts the backup, and sends it to iPhone B as plaintext through an encrypted tunnel. iPhone B receives the backup as plaintext and stores it locally, encrypting it locally with the device private key. 6) iPhone B iMessage client loads the plaintext old iMessages into the Messages client for you to read. At no point in this process would Apple have or store your iMessage private key or your device private key.

nemothekid 7y ago
You are right; Apple isn't storing your private key, they simply have access to an unencrypted dump of your iPhone at the time of iCloud backup creation. My comment implies that once you take a backup, Apple would have the ability to read all your future messages as well.
dwaite 7y ago
The encryption is a bit complex on the iPhone, because keys are typically held by the secure enclave which enforces policy on use. These keys are both used to encrypt the base filesystem, and can be applied by policy against individual files. Example policies from the Secure Enclave would be that a private key is available on first unlock, only while unlocked, only while a PIN is set, and/or whether the key should be shared with other trusted devices. The base filesystem is encrypted with a key released on boot, while individual files can be encrypted with some set of these policies. I believe this can be done either on individual files in an app's data, or as an entitlement to apply by default to the entire app. https://developer.apple.com/documentation/bundleresources/entitlements/com_apple_developer_default-data-protection https://developer.apple.com/documentation/bundleresources/en... My understanding is that files set with a policy that they are only available while the device is unlocked will still be backed up in the locally encrypted form. So, assuming Signal/WhatsApp/etc set a single flag their data is stored encrypted in iCloud. Further, per your list I suspect that the backup data is sent to/from iCloud already encrypted by a secret - but that secret is shared with iCloud for recovery and shared further on official government request. The goal there is to limit the amount of unencrypted user data sent to third party servers (in this case in the US I believe Azure-hosted storage for backups). The keys are separately stored on Apple-controlled servers in non-China countries. In China, I believe they were required by law to have the key storage instead hosted by a Chinese data center.

madeofpalk 7y ago

> all your messages will be returned. Your messages are returned via the backup, not via the "iMessage servers". Once the messages are at rest on your device, they're no longer encrypted using your "iMessage private key".