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When the cookie meets the blockchain: Privacy risks of web payments via cryptocurrencies

Steven Goldfeder, Harry Kalodner, Dillon Reisman, Arvind Narayanan

2017 · arXiv

Security & cryptographyDatabases
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From the abstract

We show how third-party web trackers can deanonymize users of cryptocurrencies. We present two distinct but complementary attacks. On most shopping websites, third party trackers receive information about user purchases for purposes of advertising and analytics. We show that, if the user pays using a cryptocurrency, trackers typically possess enough information about the purchase to uniquely identify the transaction on the blockchain, link it to the user's cookie, and further to the user's real identity. Our second attack shows that if the tracker is able to link two purchases of the same user to the blockchain in this manner, it can identify the user's entire cluster of addresses and transactions on the blockchain, even if the user employs blockchain anonymity techniques such as CoinJoin. The attacks are passive and hence can be retroactively applied to past purchases. We discuss several mitigations, but none are perfect.

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5 selected excerpts · 5 total mentions

DonHopkins
Neutral mention · rule
This series of presentations explains how ZeroStableCoin perfectly mitigates and protects users from Monstrous Cookie Attacks and Double Counting Attacks, as described in the paper by Goldfeder, Kalodner, Reisman, and Narayanan: https://www.youtube.com/watch?v=xjHSPyFjZpc https://www.youtube.com/watch?v=1ZoIP4aoM0g https://www.youtube.com/watch?v=jwoWBrT-FyU https://www.youtube.com/watch?v=h-nI7t2IJSY https://arxiv.org/abs/1708.04748 >When the cookie meets the blockchain: Privacy risks of web payments via cryptocurrencies >Steven Goldfeder, Harry Kalodner, Dillon Reisman, Arvind Narayanan >We show how third-party web trackers can deanonymize users of cryptocurrencies. We…
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present two distinct but complementary attacks. On most shopping websites, third party trackers receive information about user purchases for purposes of advertising and analytics. We show that, if the user pays using a cryptocurrency, trackers typically possess enough information about the purchase to uniquely identify the transaction on the blockchain, link it to the user's cookie, and further to the user's real identity. Our second attack shows that if the tracker is able to link two purchases of the same user to the blockchain in this manner, it can identify the user's entire cluster of addresses and transactions on the blockchain, even if the user employs blockchain anonymity techniques such as CoinJoin. The attacks are passive and hence can be retroactively applied to past purchases. We discuss several mitigations, but none are perfect.
Original comment ZeroStableCoin is out from stealth mode
osteele
Neutral mention · rule
Once an address has been doxxed, you've got a lead on any address used in a common transaction. It doesn't conclusively unmask these other addresses, so whether this counts as “really that difficult” depends on your investigative powers and your definition of “difficult”. Because of KYC[1] and AML[2], an address belonging to an exchange wallet should probably be considered doxxed. An authority can say “Hey Coinbase, I see you sent coin from address A on this date. Show me what account that came from.” CoinJoin[3] was intended to solve this problem, but apparently doesn't[6]. I was going to say that a decentralized cross-chain trading scheme[4][5] to launder through an…
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anonymous currency such as Monero or ZCash might provide anonymity, but it looks like there's enough information to correlate the transactions across chains. (Even if there weren't, cross-chain trading might practically have one of the same issues as CoinJoin: that the transaction volume is just too low to provide anonymity.) There's other cryptocurrencies designed to provide anonymity[8]. The Lighting Network[10] might add this to Bitcoin[11]; I don't know if that's still one of their goals. EDIT: I somehow missed EthanHeilman's comment, above, when I wrote this. He says pretty much everything I said about why it's hard to keep Bitcoin activity private, more clearly. I included more links, though :-) [1] "Know Your Customer", https://en.wikipedia.org/wiki/Know_your_customer [2] "Anti Money-Laundering", https://en.wikipedia.org/wiki/Money_laundering#Anti-money-la... [3] "CoinJoin", https://en.wikipedia.org/wiki/CoinJoin [4] "Atomic cross-chain trading", https://en.bitcoin.it/wiki/Atomic_cross-chain_trading [5] "First Ever Cross Chain Atomic Swap Between Bitcoin and Litecoin a Success", http://bitcoinist.com/first-ever-cross-chain-atomic-swap-bet... [6] S. Goldfeder et al, "When the cookie meets the blockchain: Privacy risks of web payments via cryptocurrencies" (2017) https://arxiv.org/pdf/1708.04748.pdf. [7] "Bitcoin Transactions Aren’t as Anonymous as Everyone Hoped ", Technology Review Aug, 2013, https://www.technologyreview.com/s/608716/bitcoin-transactio... summarizes [6]. [8] "Keybase chooses Zcash" https://keybase.io/blog/keybase-and-zcash has a fun example of address linkage. [9] Sudhir Khatwani, "9 Anonymous Cryptocurrencies You Should Know About", 2/02/18. https://coinsutra.com/anonymous-cryptocurrencies/ [10] Lightning Network, https://lightning.network. [11] Aaron van Wirdum, "How the Lightning Network Layers Privacy on Top of Bitcoin", Bitcoin Magazine, Dec 19 2016. https://bitcoinmagazine.com/articles/how-the-lightning-netwo...
Original comment Bitcoin faces regulatory crackdown, Bank of England warns
jodrellblank
Neutral mention · rule
"We show how third-party web trackers can deanonymize users of cryptocurrencies. We present two distinct but complementary attacks." - "When the cookie meets the blockchain: Privacy risks of web payments via cryptocurrencies", https://arxiv.org/abs/1708.04748
Original comment It’s time to kill the web app
randomwalker
Neutral mention · rule
I'm a co-author of this paper. It's available here: https://arxiv.org/pdf/1708.04748.pdf The surprise here isn't that Bitcoin isn't perfectly anonymous. There are two new findings. The first is the extent to which your Bitcoin payment details get leaked to third party trackers. I've been writing about the excesses of third party tracking for years [1], and I'm pretty jaded, but the extent of the leaks surprised me. The second main finding is that CoinJoin isn't enough to protect yourself. We tested this on our own transactions, but also by coming up with a way to identity essentially all existing CoinJoins on the blockchain and analyzing their anonymity. [1] http://randomwalker.info/web-privacy/
Original comment Web merchants routinely leak data about Bitcoin purchases

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