Commit 475fc5ea authored by Justin Ehrenhofer's avatar Justin Ehrenhofer Committed by GitHub
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Update 2017-04-19-an-unofficial-response-to-an-empirical-analysis-of-linkability.md

parent 85d4d2e1
......@@ -8,7 +8,7 @@ author: Justin Ehrenhofer (SamsungGalaxyPlayer) and the Monero community
# Preface
This release attempts to contain the opinions of the Monero community. It is possible that not every viewpoint is expressed, but this paper includes the best response to the author's ability that encapsulates all these opinions. The author opens all discussion to how certain viewpoints are represented, and the purpose of this response is solely for easier documentation by interested parties. He have done the best to include sources wherever possible, and to be as accurate as possible. For any concerns with this publication, please express them to the [author's Reddit account](https://www.reddit.com/u/SamsungGalaxyPlayer) or on [the Monero subreddit](https://www.reddit.com/r/Monero/).
This release attempts to contain the opinions of the Monero community. It is possible that not every viewpoint is expressed, but this paper includes the best response to the author's ability that encapsulates all these opinions. The author opens all discussion to how certain viewpoints are represented, and the purpose of this response is solely for easier documentation by interested parties. He has done the best to include sources wherever possible, and to be as accurate as possible. For any concerns with this publication, please express them to the [author's Reddit account](https://www.reddit.com/u/SamsungGalaxyPlayer) or on [the Monero subreddit](https://www.reddit.com/r/Monero/). This version has been updated for clarity, though the core content has remained unchanged.
The Monero contributors and community at large always appreciate any research done on Monero's technology. They heavily encourage constructive criticism of all cryptocurrencies.
......@@ -38,13 +38,13 @@ The following are the recommendations listed in the paper and responses to them:
The Monero community would like to list several concerns with this research paper. They are documented below:
1. We believe that a large proportion of 0-mixin transactions are pool payouts. These transactions should come to no one's surprise that they are traceable, since the pools themselves publish the payment amount to each transaction hash. Thus, we believe that the claims stemming from the traceability of transactions before 0-mixin transactions were banned to be misplaced. If, for example, 50% of non-pool payouts used a positive mixin and 0% of pool payouts did, then the traceability is less for the transactions that use these mixins and greater for pool payouts. We recommend that this is acknowledged in a later iteration of the paper. Ideally, the proportion of pool payouts can be found and compared to the proportion of non-pool payouts, with different traceability proportions for each. There are several reasons why these transactions neither reduce the anonymity of the transaction itself or other users. In regards to the former, coinbase transactions (ie: new rewards given to the pool) are 0-mixin, since having mixins is useless if the input is brand new and seen for the first time. Anyone who mines understands that the source of thier money is clear. In regards to other transactions, the pool payouts occur within the day, reducing the negative impact spending these transactions has on other users who may have borrowed the input for their transaction. Thus, pool payouts should include additional mixins, but excluding them has relatively minimal harm. The larger threat is the opportunity cost, where the additional mixins could provide greater levels of privacy for other users. Furthermore, all transactions are still unlinkable by the MRL definition of the word (see "Other Information" point 4) ([source](https://www.reddit.com/r/Monero/comments/65dj7u/an_empirical_analysis_of_linkability_in_the/dga1rza/?context=1)).
1. We believe that a large proportion of 0-mixin transactions are pool payouts. These transactions should come to no one's surprise that they are traceable, since the pools themselves publish the payment amount to each transaction hash. Thus, we believe that the claims stemming from the traceability of transactions before 0-mixin transactions were banned to be misplaced. If, for example, 50% of non-pool payouts used a positive mixin and 0% of pool payouts did, then the traceability is less for the transactions that use these mixins and greater for pool payouts. We recommend that this is acknowledged in a later iteration of the paper. Ideally, the proportion of pool payouts can be found and compared to the proportion of non-pool payouts, with different traceability proportions for each. There are several reasons why these transactions neither reduce the anonymity of the transaction itself or other users. In regards to the former, coinbase transactions (ie: new rewards given to the pool) are 0-mixin, since having mixins is useless if the input is brand new and seen for the first time. Anyone who mines understands that the source of their money is clear. In regards to other transactions, the pool payouts occur within the day, reducing the negative impact spending these transactions has on other users who may have borrowed the input for their transaction. Thus, pool payouts should include additional mixins, but excluding them has relatively minimal harm. The larger threat is the opportunity cost, where the additional mixins could provide greater levels of privacy for other users. Furthermore, all transactions are still unlinkable by the MRL definition of the word (see "Other Information" point 4) ([source](https://www.reddit.com/r/Monero/comments/65dj7u/an_empirical_analysis_of_linkability_in_the/dga1rza/?context=1)).
2. We think further emphasis should have been placed in the paper to explain that the claims are only minimally applicable with the state of Monero transactions since March 2016, with the relevance decreasing over time. Though it is mentioned that their first analysis method has little if any current or future relevance, the claims still include these transactions. 0-mixin transatctions were prohibited in March 2016, and most transaction volume for the year occurred during and after August. Nevertheless, many of these post-March transactions have inputs that can be deducible, but the traceability typically is not as severe as with 0-mixin transactions. The transactions that are most vulnerable are those in 2014 and 2015, as well as some time needed for the network to recover.
3. Under the "ethics" section, they state that the paper was published immediately before countermeasures could be deployed. While this is understandable from the given perspective that the blockchain history is not going away anytime soon (or ever), we wish that they had given us an advance copy of the finished draft so that we could have discussed our concerns with the report itself. We wish not to censor any of the research (instead, we encourage research!); however, we hope that future care can be taken before the release of misleading assertions.
4. Andrew Miller was named in the paper as a consultant to the Zerocoin Electric Coin Company and a board member of the ZCash Foundation. ZCash is a cryptocurrency with a focus on privacy that uses different technology than Monero. However, [he downplayed his involvement in an interview](https://cointelegraph.com/news/monero-transactions-history-can-be-revealed-and-exposed-research) about this paper. We feel author involvement in cryptocurrencies with similar interests should be fully disclosed, though he did refer people to the first page of the report. Nevertheless, we feel this is extremely poor form.
4. Andrew Miller was named in the paper as a consultant to the Zerocoin Electric Coin Company and a board member of the ZCash Foundation. ZCash is a cryptocurrency with a focus on privacy that uses different technology than Monero. However, [he downplayed his involvement in an interview](https://cointelegraph.com/news/monero-transactions-history-can-be-revealed-and-exposed-research) about this paper. We feel author involvement in cryptocurrencies with similar interests should be fully disclosed, though he did refer people to the first page of the report. Nevertheless, we feel that Miller's disclosure of his contribution to a competing project was unsatisfactory, given the severity of the allegations in the paper.
# Other Information
......@@ -76,7 +76,7 @@ We appreciate the effort that went into this research paper, but we suggest the
# Appendix
**Figure 5 from the report showing the fraction of deducible outputs. Notice the large drops following block height 1,000,000, when 0-mixin transactions were prohibited. Furthermore, these outputs likely do not include all those used in a singe transaction. For instance, for a mixin 9 transaction, 5 may be deduced. This means that the transaction would be reported here as deducible, even though it is not traceable.**
**Figure 5 from the report showing the fraction of deducible outputs. Notice the large drops following block height 1,000,000, when 0-mixin transactions were prohibited. Furthermore, these outputs likely do not include all those used in a single transaction. For instance, for a mixin 9 transaction, 5 may be deduced. This means that the inputs would be reported here as deducible, even if the transaction is not traceable.**
<img src="/blog/assets/linkability-response/figure5.jpg" style="width: 600px;"/>
......@@ -94,10 +94,10 @@ This is a tweet from a contributor to the paper.
<img src="/blog/assets/linkability-response/tweet.jpg" style="width: 600px;"/>
This image is from the [CoinTelegraph interview](https://cointelegraph.com/news/monero-transactions-history-can-be-revealed-and-exposed-research). Based on the wording, you may think an attacker could determine with certainty which input is yours. However, in reality, the attacker can guess and be correct less than half of the time. Furthermore, even if the attacker guesses correctly, there is no way of proving this with certainty with data from the blockchain alone.
This image is from the [CoinTelegraph interview](https://cointelegraph.com/news/monero-transactions-history-can-be-revealed-and-exposed-research). Based on the wording, you may think an attacker could determine with certainty which input is yours. However, the attacker can guess and be correct less than half of the time. Furthermore, even if the attacker guesses correctly, there is no way of proving this with certainty with data from the blockchain alone.
<img src="/blog/assets/linkability-response/cointelegraph.jpg" style="width: 600px;"/>
Andrew Miller asked us to include other statements from the researchers or ZCash Foundation members that we feel is misleading. This paper is not supposed to be a comprehensive list of such statements. It is only really useful in providing a few examples.
Andrew Miller asked us to include other statements from the researchers or ZCash Foundation members that we feel is misleading. This paper is not supposed to be a comprehensive list of such statements. It is only useful in providing a few examples.
This draft was shown to Andrew Miller before release on the website. Some of his considerations have been included in this response.
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