[taler-docs] branch master updated: Editing... fee levels in case of misuse

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The following commit(s) were added to refs/heads/master by this push:
     new f11b4ef  Editing... fee levels in case of misuse
f11b4ef is described below

commit f11b4ef1bac07d0c7c2ca80c730b43f89c30ff38
Author: Stefan Kügel <skuegel@web.de>
AuthorDate: Fri Jan 15 20:48:39 2021 +0100

    Editing... fee levels in case of misuse
---
 design-documents/012-fee-schedule-metrics.rst | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/design-documents/012-fee-schedule-metrics.rst 
b/design-documents/012-fee-schedule-metrics.rst
index f4b15a3..e788597 100644
--- a/design-documents/012-fee-schedule-metrics.rst
+++ b/design-documents/012-fee-schedule-metrics.rst
@@ -117,9 +117,9 @@ During deposit, the Exchange logic compares the public key 
of each coin with the
 
 * **Deposit** from the seller's point of view:
 
-If an Exchange operator charges relatively high deposit fees, sellers have a 
means to set a boundary for the deposit fee amount and split it in two amounts. 
As pointed out before, a seller must bear deposit fees, but only up to the 
maximum determined by the variable ``default_max_deposit_fee``, which every 
seller specifies individually.
+If an Exchange operator charges relatively high deposit fees, sellers must 
have a means to split it into two amounts. Sellers determine the amount they 
maximally want to bear by setting the variable ``default_max_deposit_fee``, 
which every seller specifies individually. The surmounting amount of the 
deposit fee is to be borne by the buyers.
 
-Deposit fees will also affect refund transactions, for example when a rebate 
is given by the seller to the customer. Only in the case of a complete 
withdrawal from the contract by the seller does the refund transaction exempt 
the buyer from the deposit fee. In that case, the refund transaction incurs the 
'Refresh' fee portion borne by the buyers. If the seller's refund is partial, 
only the seller's deposit fee is waived, which means from the buyer's 
perspective a partially refunded purch [...]
+Deposit fees will also affect refund transactions, for example when a rebate 
is given by the seller to the customer. Only in the case of a complete 
withdrawal from the contract by the seller does the refund transaction exempt 
the buyer from the deposit fee. In that case, the refund transaction incurs the 
'Refresh' fee, borne entirely by the buyers. If the seller's refund is partial, 
only the seller's deposit fee is waived, which means from the buyer's 
perspective a partially refunded pur [...]
 
 Generally, sellers want to ensure that:
 (1) the exchange selected by the buyers complies with the regulatory 
requirements of the supervisory authorities (e.g. BaFin) and with anti-money 
laundering laws (AML); 
@@ -177,7 +177,7 @@ The closing transaction does not affect sellers in any way.
 Fee levels in case of misuse
 ----------------------------
 
-Normally, the payment process involves the fee types **Withdrawal**, 
**Deposit** and **Wire fee** - when the amount to be paid is settled with a 
coin of the exactly matching denomination. For any other amount for which a 
coin of higher denomination is used, the refresh transaction will generate 
change, i.e. post one or more fresh coins to the wallet until the difference is 
reached.
+Normally, the payment process involves the fee types **Withdrawal**, 
**Deposit** and **Wire fee** - given the case the amount to be paid is settled 
with a coin of the exactly matching denomination. For any other amount for 
which a coin of higher denomination is used, the refresh transaction will 
generate change, i.e. post one or more fresh coins to the wallet until the 
difference is reached.
 
 However, refresh transactions can be triggered anonymously an unlimited number 
of times by malicious parties, thus harming Exchange operators. Exchange 
operators must therefore be able to take action in the event of misuse with the 
help of different fees:
 
@@ -185,6 +185,11 @@ However, refresh transactions can be triggered anonymously 
an unlimited number o
 
 * Abuse due to ``deposit transactions`` is unlikely as the Exchange operator 
will usually charge deposit fees on every denomination to generate income 
respectively to cover costs.
 
+* Abuse due to ``refresh transactions`` is possible and requires a 
differentiated treatment: The normal case for refresh operations is given, when 
wallets obtain fresh coins for a used coin of higher denomination than the 
amount to be paid. In this case, an Exchange operator will not charge a refresh 
fee on payments with coins of unsuitable denomination. Only in the case of 
abuse the Exchange operator must charge this fee when a malicious party 
triggers refreshes en masse. These misuse c [...]
+(1.) arbitrary transaction aborts;
+(2.) arbitrary repeated refunds (which, however, must be triggered by 
malicious sellers - costs are borne on a case-by-case basis).
+In extreme cases of abuse - when an exchange suffers from arbitrarily 
triggered refresh transactions, the Exchange operator must set the refresh fee 
or increase it and thus charge all coin owners whose coins were signed by that 
exchange.
+
 * Abuse due to ``closing transactions`` and the involved remittances 
(withdrawing to the wallet failed within the given time frame, Exchange has to 
wire the value to the originating account) burdens the Exchange operator with 
costs for wire transfers; to prevent this, the Exchange operator can introduce 
a fee by adjusting the **closing** variable.
 
 Alternatives

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