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[taler-docs] branch master updated (2acbc5f -> fb9a5e4)

From: gnunet
Subject: [taler-docs] branch master updated (2acbc5f -> fb9a5e4)
Date: Mon, 19 Apr 2021 14:42:18 +0200

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

dold pushed a change to branch master
in repository docs.

    from 2acbc5f  expand Anastasis UI document
     new ca6c473  fix regex
     new fb9a5e4  pass over DD13

The 2 revisions listed above as "new" are entirely new to this
repository and will be described in separate emails.  The revisions
listed as "add" were already present in the repository and have only
been added to this reference.

Summary of changes:
 design-documents/013-peer-to-peer-payments.rst | 121 +++++++++++++++++++++++--
 design-documents/018-contract-json.rst         |   2 +-
 2 files changed, 116 insertions(+), 7 deletions(-)

diff --git a/design-documents/013-peer-to-peer-payments.rst 
index 4bdd492..5797a72 100644
--- a/design-documents/013-peer-to-peer-payments.rst
+++ b/design-documents/013-peer-to-peer-payments.rst
@@ -61,9 +61,9 @@ New Terminology
 * An ``account`` is a non-expiring reserve for which entity knowing the
   reserve private key has completed a KYC procedure sufficient to enable
   receiving income under that address.
-* A ``pouch`` is a public-private key pair where the public key is
+* A ``purse`` is a public-private key pair where the public key is
   an exchange address from which any owners of an account
-  can pick up an amount left at a ``pouch`` assuming they know the pouches
+  can pick up an amount left at a ``purse`` assuming they know the purse
   private key.
 * A ``wad`` is an exchange-to-exchange wire transfer that wires money
   into a group of accounts at the target exchange.
@@ -84,7 +84,7 @@ Account creation and withdrawal
    target address (for which the payee knows the corresponding
    account private key).
 2. When withdrawing from an account, the exchange first checks if the
-   customer has satisfied the KYC requirements. If not, the consumer
+   customer has satisfied the KYC requirements. If not, the customer
    is redirected to a Web page where they can perform the necessary
    KYC operation.
 3. For this, the exchange wire gateway is extended with a request to
@@ -203,6 +203,72 @@ Payment into known account at a remote exchange
    is needed to lookup the **wad** data at remote exchanges.
+C2C Payment Metadata
+The standard Taler Customer-to-Merchant payments always use a contract terms
+JSON object to record the modalities of the payment and the resulting
+obligations of a successful payment.
+The contract terms concept does not directly carry over to
+C2C payments, because:
+* Either party may initiate the payment
+* The payee does not have a merchant public key, and
+  at the time of payment initiation, the payee account might not yet
+  be known.
+* There is no nonce that the customer generates and uses to prove that they
+  uniquely "own" the contract terms.
+* There is no negotiation of trusted auditors / exchanges possible or 
+Metadata for C2C payments can be exchanged in two ways:
+1. Inline, as part of the payment request / payment offer.
+2. As an annotation on the purse, encrypted with the purse's public key.  The
+   exchange may charge for storing the annotation.
+   In case of a "payment request purse", the fee should be
+   taken from an account provided by the payee (which may even
+   offer a limited number of free P2P payment initiations per time period).
+   In case of a "payment offer purse", the fee should be taken from the
+   coins deposited into the purse.
+Cross-exchange C2C payment request:
+* Bob borrowed 15 Eur from Alice to buy a train ticket.  A few days later,
+  Alice wants her money back.  She creates a request for payment in her wallet.
+  The wallet creates a pouch for 15 Eur at the only exchange that Alice is 
+  using.  The wallet shows her a
+  ``taler://payment-request/{EXCHANGE_URL}/{POUCH_PRIV}?i=Please+pay+me+Bob``
+  link that she can share with Bob.  Bob receives the link and opens it with
+  his Taler wallet.  Bob is using a different EUR exchange than Alice.  Bob's
+  wallet makes a ``/wad`` request to his own exchange.  Shortly after, Alice's
+  exchange receives the wad from Bob's exchange, and credits the money into
+  Alice's pouch.
+  * How does Bob find out if Alices exchange supports a wad transfer from
+    Bob's exchange?
+  * How does Bob get a "receipt" to prove that he paid Alice?  Is some 
+    from Bob's exchange enough, or should Bob also request a signature for 
+    exchange once the money has arrived?  Bob's wallet could poll
+    the purse at Alice's exchange for a receipt.
+Cross-exchange payment offer:
+* Carol wants to send some money to Dave as a birthday gift.  Carol knows that
+  Dave is using Taler, but she doesn't know which exchange he is using.  She
+  opens her Taler wallet and initiates a P2P payment.  She sends the
 in an e-mail to Dave.
+  Dave opens they link in the e-mail with his Taler wallet.
+  Since Dave is using a different exchange than Alice, Dave's wallet
+  issues a ``/wad`` request to Alice's exchange.  Shortly after,
+  Dave's exchange receives the wad, and credits Dave's account with the money.
 Additional considerations
@@ -257,16 +323,59 @@ The overall changes required are not small:
 * New exchange table(s) required to store inbound amounts by account.
   Likely two tables, one for local exchange p2p and one for remote exchange p2p
-* New exchange table for pouches required (for remote p2p payments).
-* New exchange logic required to make ``transfers`` requests for pouches
+* New exchange table for purses required (for remote p2p payments).
+* New exchange logic required to make ``transfers`` requests for purses
   (another separate process).
 * New ``/account/$ACCOUNT_PUB/kyc`` endpoint required.
 * New ``/purse/$PURSE_PUB/merge`` endpoint required.
 * Additional tables to be verified by the auditor.
-* ``taler-exchange-wirewatch`` needs to support receiving pouch closures
+* ``taler-exchange-wirewatch`` needs to support receiving purses closures
   and exchange-to-exchange wire transfers with WTIDs.
 Aside from implementation complexity, the solution has the following drawbacks:
 * If a p2p payment failed (say the receiver lost the account private key),
   the customer's money can be forfeit.
+Q / A
+* Q: Why are direct payments into accounts allowed?
+  * A: Direct payments into accounts are used by the customer
+    to fund the expenses for using the account.  They should not
+    be used for payments between customers, as contract terms for
+    the ``/deposit`` of coins can't be negotiated.  Furthermore,
+    the sender of the payment can't be sure that the account of
+    the sender is still valid.
+* Q: Who "owns" a purse?  The payer of payee?
+  * Both.  Ownership is shared.  Either the payer issues
+    a refund on the purse, or the payee claims it by merging
+    it with one of their accounts.
+* Q: Are purses created with a pre-determined "capacity"?
+  * A: Yes.  Otherwise there would be weird failure modes when the payee
+    merges the purse before the payer fully deposited into it.
+* Q: Are account public keys considered private or public data?
+  * A: Private.  Making it public would make it too easy
+    to accidentally send payments that nobody can receive, because
+    the account is wrong/lost.  Furthermore, making the account
+    public makes it easy to receive unsolicited payments without
+    consent from the payee.  Since Taler should be as cash-like
+    as possible, we might want to avoid that, especially
+    for payees who aren't merchant.
+* Q: Why do merchant payments not use purses?
+  * A: Refunds aren't possible with purses, the customer can't prove that
+    they own the contract terms (contract terms claiming isn't interactive).
+    * All these issues could be addressed though.  But that
+      would be a major "Taler 2.0 / 3.0" protocol change
diff --git a/design-documents/018-contract-json.rst 
index 7c62600..4208feb 100644
--- a/design-documents/018-contract-json.rst
+++ b/design-documents/018-contract-json.rst
@@ -46,7 +46,7 @@ In order to make it easy to get a canonical representation 
for JSON contract
 terms, the following restrictions apply:
 * Member names are restricted:  Only strings matching the regular expression
-  ``0-9A-Z_a-z`` or the literal names ``$forgettable`` or ``$forgotten`` are
+  ``^[0-9A-Z_a-z]+$`` or the literal names ``$forgettable`` or ``$forgotten`` 
   allowed.  This makes the sorting of object members easier, as RFC8785
   requires sorting by UTF-16 code points.
 * Floating point numbers are forbidden.  Numbers must be integers in the range

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