[taler-docs] branch master updated: recovery of subscriptions as discussed with Leif

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grothoff pushed a commit to branch master
in repository docs.

The following commit(s) were added to refs/heads/master by this push:
     new 62110e0d recovery of subscriptions as discussed with Leif
62110e0d is described below

commit 62110e0de498a772acb0175b8227aba2c3a03305
Author: Christian Grothoff <grothoff@gnunet.org>
AuthorDate: Tue Aug 15 13:00:16 2023 +0200

    recovery of subscriptions as discussed with Leif
---
 design-documents/046-mumimo-contracts.rst | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/design-documents/046-mumimo-contracts.rst 
b/design-documents/046-mumimo-contracts.rst
index 1089215a..326ec43d 100644
--- a/design-documents/046-mumimo-contracts.rst
+++ b/design-documents/046-mumimo-contracts.rst
@@ -30,6 +30,9 @@ We want Taler to support various interesting use-cases:
     with unlinkability and anonymity (modulo there being other users eligible
     for the discount).
 
+  - Subscription tokens lost (due to loss of device without backup) should
+    be recoverable from any previous backup of the subscription.
+    
   - Currency conversion, that is exchanging one currency for another.
 
   - Donations, including privacy-preserving tax receipts that prove that the
@@ -508,6 +511,12 @@ higher-priced alternative offers.
 
 Subscription tokens are "critical" in that a wallet implementation must
 understand them before allowing a user to interact with this class of token.
+Subscription token secrets should be derived from a master secret associated
+with the subscription, so that the private keys are recoverable from backup.
+To obtain the blind signatures, a merchant must offer an endpoint where
+one can submit the public key of the N-1 subscription token and obtain the
+blinded signature over the N-th subscription token.  The wallet can then
+effectively recover the subscription from backup using a binary search.
 
 The merchant SPA should allow the administrator to create (maybe update) and
 delete subscriptions. Each subscription is identified by a subscription
@@ -521,6 +530,8 @@ respective cryptographic fields for the respective time 
period and
 subscription label.
 
 
+
+
 Discounts
 ---------
 

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