Add back the retrieved user into the Application's contact list | Sub task of #87

[Winterhart]

This is the final result of retrieve contact story (#87). Upon pressing on panic button the data of Briar will be deleted, if the user connect again with the same account, he should be able to get its contacts back again

Problems with this idea:

• Local database is destroyed upon using the panic button and encryption keys are lost
• Adding someone is only possible using the complex QRCode procedure
• If another user with the same name press get back my contacts
• We can't 'workaround' using QRCode procedure as the main data to produce QRCode is a encrypted string that is random at each QRCode. ( https://github.com/jhubscher/briarproject_390/blob/dev/briar-android/src/main/java/org/briarproject/briar/android/keyagreement/ShowQrCodeFragment.java )

More architecture details in following comments...

Risks:

• (1) Able to extract encryption keys for the current user?
• (2) Able to extract encryption keys for user / conversation?
• (3) Are encryption keys changing (YES/NO) , how often?
• (4) Are we able to recreate a contact (Overwrite QR Procedure)?
• (5) In which context are we able to extract key?

I will go through the risk and find out if it's possible or not by doing an analysis of the main class in charge of adding Contact: https://github.com/jhubscher/briarproject_390/blob/561facd9848c0bcf68c80f5b34726cce18c4b1ff/bramble-core/src/main/java/org/briarproject/bramble/contact/ContactExchangeTaskImpl.java

[Winterhart]

The entire process of adding contact is covered into this sequence diagram

As result, using the sequence diagram we will try to ensure that a workaround is possible (Risk 2, 3, 5, 4)

[Winterhart]

RESUME OF THE ADD CONTACT TRANSACTION:

What can we conclude from this?

• During the whole time both users need to be connected to same network.
• A timestamp is preventing any attempt to make a workaround.
• The transaction is made one device after the other as when you play monopoly (alice boolean variable)
• We can't go directly to addContact in database as the transaction need remoteProperties from the other device
• remoteProperties is generated using random defined key masterkey random on each transaction
• All information are encrypted and passed using array of bytes

[Winterhart]

This is an analysis of the random key generation:

BriarKeyGenerationAnalysis.txt

[Winterhart]

Conclusion:

Risks:

• (1) Able to extract encryption keys for the current user? -> We don't have a static key for add contact transaction. Can we get the custom database encryption key? (unresolved)
• (2) Able to extract encryption keys for user / conversation? -> No everything is random and transferred using a socket connection halfClosed
• (3) Are encryption keys changing (YES/NO) , how often? YES, when you open the app or each time you press on the '+' button
• (4) Are we able to recreate a contact (Overwrite QR Procedure)? No, to start the QrCode we are required to have an activity and an AppContext relevant. Therefore the procedure can't be short circuit or simulated (see Sequence diagram)
• (5) In which context are we able to extract key? (unresolved for now)

[Winterhart]

Here are few possible workarounds to make the solution work: https://docs.google.com/presentation/d/1v2SS1u_5MmU8ARhvmTJPyNMfyKEGds33H1Bg23A4vbY/edit?usp=sharing

[Winterhart]

Conclusion: The story is not feasible with our current remaining resources

[Winterhart]

@mehranhassani Can you review this issue ?