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[taler-docs] branch master updated: new, simplified backup proposal

From: gnunet
Subject: [taler-docs] branch master updated: new, simplified backup proposal
Date: Fri, 06 Nov 2020 17:43:17 +0100

This is an automated email from the git hooks/post-receive script.

dold pushed a commit to branch master
in repository docs.

The following commit(s) were added to refs/heads/master by this push:
     new acb799f  new, simplified backup proposal
acb799f is described below

commit acb799f34f2d576b39203012d0c603ffaf31a232
Author: Florian Dold <>
AuthorDate: Fri Nov 6 17:42:35 2020 +0100

    new, simplified backup proposal
 design-documents/005-wallet-backup-sync.rst |   6 +-
 design-documents/009-backup.rst             | 105 ++++++++++++++++++++++++++++
 design-documents/index.rst                  |   1 +
 3 files changed, 111 insertions(+), 1 deletion(-)

diff --git a/design-documents/005-wallet-backup-sync.rst 
index 26dbbf1..20fce37 100644
--- a/design-documents/005-wallet-backup-sync.rst
+++ b/design-documents/005-wallet-backup-sync.rst
@@ -3,7 +3,11 @@ Design Doc 005: Wallet Backup and Sync
 .. warning::
-  This is an unfinished draft.
+  This document is deprecated.  We have decided to first
+  implement backup, and tackle sync later.
+  The multi-device sync described in this document would lead
+  to a bad/unexpected user experience that does not justify the
+  conceptual / implementation complexity.
diff --git a/design-documents/009-backup.rst b/design-documents/009-backup.rst
new file mode 100644
index 0000000..7ec8be2
--- /dev/null
+++ b/design-documents/009-backup.rst
@@ -0,0 +1,105 @@
+Design Doc 009: Wallet Backup
+This document describes the backup system used by Taler wallets.
+This is the second, simplified iteration of the proposal, which leaves
+out multi-device synchronization.
+* Backup must work both with and without Anastasis
+  * When not using Anastasis, the user is responsible for keeping
+    their wallet's root secret safe.
+* Arbitrary number of backup providers must be supported
+* Minimize information leaks / timing side channels **if** requested by the 
+* Minimize potential to lose money or important information
+* Since real-time sync is not supported yet, wallets should have a feature
+  where their whole content is "emptied" to another wallet, and the wallet is
+  reset.
+* Even without real-time sync, the backup data must support merging with old, 
existing wallet
+  state, as the device that the wallet runs on may  be restored from backup or 
be offline
+  for a long time.
+Solution Overview
+Each wallet has a 64 byte wallet root secret, which is used to derive all 
other secrets
+used during backup, which are currently:
+1. The sync account key for a sync provider, derived via the sync provider's 
base URL.
+2. The symmetric key used to encrypt the backup blob
+If the user chooses to use Anastasis, the following information is backed up 
in Anastasis:
+* list of used backup providers
+* wallet root secret
+Supported Operations
+* **restore-from-anastasis**:  Start Anastasis recovery process.  This requires
+  the wallet backup state to be "uninitialized".
+* **restore-from-recovery-secret**:  This requires the wallet backup state to 
be uninitialized.
+* **add-provider** / **remove-provider**:  Add/remove a sync provider from the
+  list of providers.  Adding a provider will cause payment(s) to the provider
+  to be scheduled according to the provider's terms.  If the wallet backup
+  state is "uninitialized", adding a provider will set the backup state to
+  "initialized" with a fresh wallet root key.  Changing the provider list will
+  also update the backup provider URL list in the  anastasis core secret.
+* **abandon** / **takeover**: When the user wants to stop using a wallet on a 
+  device, another wallet can "take over" by reading the recovery secret of the 
abandoned wallet.
+  The abandoned wallet marks explicitly in its backup blob that it is 
+  Abandoning a wallet will set the backup state to "uninitialized".
+* **backup**: Do a backup cycle.
+Backup Format
+TBD.  Considerations from :doc:`005-wallet-backup-sync` still apply,
+especially regarding the CRDT.
+Initial User Experience
+The user will be asked to set up backup&sync (by selecting a provider)
+after the first withdrawal operation has been confirmed.  After selecting
+the backup&sync providers, the user will be presented with a "checklist" that
+contains an option to (1) show/print the recovery secret and (2) set up 
+The wallet will initially only withdraw enough money to pay the
+backup&sync/anastasis providers.  Only after successful backup of the wallet's
+signed planchets, the full withdrawal will be completed.
+Open Questions
+* Should the wallet root secret and wallet database be locally encrypted
+  and protected via a passphrase?
+* What happens if the same Anastasis user has multiple wallets?  Can Anastasis 
+  support multiple "instances" per application?
+Future Work
+* Incremental backups?
+  * Instead of one big blob that always needs to be read/written, we could 
have (1) a
+    limited length append-only journal and (2) a merkle tree so that the 
backup blob can
+    be updated incrementally once the journal is full.
+  * Leaks more information and is more complex.
+* Real-time synchronization, either over some signaling server
+  or P2P connectivity (WebRTC, etc.)
diff --git a/design-documents/index.rst b/design-documents/index.rst
index 38825b2..55dd8c1 100644
--- a/design-documents/index.rst
+++ b/design-documents/index.rst
@@ -18,3 +18,4 @@ and protocol.
+  009-backup

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