review formatting

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Florian Dold 2017-05-17 15:25:25 +02:00
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@ -96,34 +96,58 @@ is also very overloaded (there is a 2 page notation table!).
Specific comments:
- I would expect the “Security Model” section (Section 1.3) to actually explain (even in an informal way) the desired properties of the proposed scheme. These should include double-spending detection security, unforgeability, user anonymity and more importantly the new type of security introduced by coin refresh (this should be a property that guarantees that a user cannot re-fresh a coin for value more than the one that the “dirty” coin is carrying) Instead it just mentions some of the tools used in the proposed scheme (i.e. FDH signatures, cut-and-choose and what kind of security they offer).
- I would expect the “Security Model” section (Section 1.3) to actually explain
(even in an informal way) the desired properties of the proposed scheme.
These should include double-spending detection security, unforgeability, user
anonymity and more importantly the new type of security introduced by coin
refresh (this should be a property that guarantees that a user cannot re-fresh
a coin for value more than the one that the “dirty” coin is carrying) Instead
it just mentions some of the tools used in the proposed scheme (i.e. FDH
signatures, cut-and-choose and what kind of security they offer).
- Related work missing: there has been previous work in “payments with refunds”. Please look at Rupp et al “P4R: Privacy-Preserving Pre-Payments with Refunds for Transportation Systems” where instead of refreshing coins, the unused amount is accumulated in some token that can later be used. How would you compare with that system?
- Related work missing: there has been previous work in “payments with
refunds”. Please look at Rupp et al “P4R: Privacy-Preserving Pre-Payments
with Refunds for Transportation Systems” where instead of refreshing coins, the
unused amount is accumulated in some token that can later be used. How would
you compare with that system?
-Found the discussion on Bitcoin too long and unnecessary - the proposed system is not decentralized anyway
- Found the discussion on Bitcoin too long and unnecessary - the proposed
system is not decentralized anyway
-Referencing a system (Goldbergs HINDE) that is not published makes impossible for the reviewer to check any arguments.
- Referencing a system (Goldbergs HINDE) that is not published makes
impossible for the reviewer to check any arguments.
-Section 4.1, step 1: is W_p = w_s * G? Also where is blinding factor b selected from? What does it mean to “commit to disk”? The customer commits and keeps the commitment local? Where is this used?
- Section 4.1, step 1: is W_p = w_s * G? Also where is blinding factor b
selected from? What does it mean to “commit to disk”? The customer commits
and keeps the commitment local? Where is this used?
-Section 4.1, step 3, what is the key K used in FDH? Also is S_w(B) a standard signature?
- Section 4.1, step 3, what is the key K used in FDH? Also is S_w(B) a standard
signature?
-Section 4.1, step 4, How can the exchange know that this was indeed a new withdrawal request? If a new blinding factor b is used, then a customer can create multiple “freshly” looking requests for the same C_p. (Also a minor point: 2nd line also reads as “if the same withdrawal request was issued before the exchange will send S_K(B)”
- Section 4.1, step 4, How can the exchange know that this was indeed a new
withdrawal request? If a new blinding factor b is used, then a customer can
create multiple “freshly” looking requests for the same C_p. (Also a minor
point: 2nd line also reads as “if the same withdrawal request was issued before
the exchange will send S_K(B)”
-Section 4.2, it seems that a customer can use a coin of value say $10 to multiple transactions of <= $10 in total. I.e. it can first a pay a merchant M1 $2 and then a merchant M2 another $5 dollars. In that case the exchange can link those two payments together. Sure, it might not know who is the owner of the coin (i.e. cannot link with withdrawal) but this is still an anonymity problem.
- Section 4.2, it seems that a customer can use a coin of value say $10 to
multiple transactions of <= $10 in total. I.e. it can first a pay a merchant
M1 $2 and then a merchant M2 another $5 dollars. In that case the exchange can
link those two payments together. Sure, it might not know who is the owner of
the coin (i.e. cannot link with withdrawal) but this is still an anonymity
problem.
-Section 4.3, doesnt seem very fair to compare with Zcash or at least it should be highlighted that a quite weaker level of anonymity is achieved.
- Section 4.3, doesnt seem very fair to compare with Zcash or at least it
should be highlighted that a quite weaker level of anonymity is achieved.
-Section 4.3, step 1, where is the key t_s^(i) selected from? What does S_{C} denotes? Is that a commitment (as noted in the text) or a signature (as noted in notation table?).
- Section 4.3, step 1, where is the key t_s^(i) selected from? What does S_{C}
denotes? Is that a commitment (as noted in the text) or a signature (as noted
in notation table?).
-Section 4.3 In this protocol I would expect the customer to somehow “prove” to the exchange what is the remaining value of the dirty coin. I do not see this happening. How does this part of the protocol ensure that a user cannot just refresh a coin for one of a much bigger value than the remaining one?
Typos
Sec. 3.1 “cryptographily” -> cryptographically
Sec 4.2, Step 1 “a exchange” -> an exchange
Sec 4.3, 3rd line should be -> at the same time
- Section 4.3 In this protocol I would expect the customer to somehow “prove”
to the exchange what is the remaining value of the dirty coin. I do not see
this happening. How does this part of the protocol ensure that a user cannot
just refresh a coin for one of a much bigger value than the remaining one?
----------------------- REVIEW 3 ---------------------