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I'm looking for a numerical privacy scoring system that estimate the degree of linkage between the members of a key pool (or even just individual key pairs). Ideally, the method should be easy to understand and apply.

I'm aware of "taint analysis" as offered by blockchain.info. There's also discussion in these papers:

What else has been done to quantitate Bitcoin user privacy? I'm most interested in ways to compute a benchmark score that tells a user how closely linked the the members of a key pool are, or how closely linked two individual key pairs are.

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Here is a great video in which they asked: given 1 address I know belonging to someone, how many other addresses can I associate with that particular wallet. It turned out to be about 75%.

The method detailed in the video uses a few assumptions about how wallets work.

  1. Multi-input heuristic: All inputs in a transaction belong to the same wallet.
  2. Shadow change heuristic: Change public keys have never been seen before on the blockchain.
  3. Consumer change heuristic: Transactions from consumer wallets have 2 or less outputs.
  4. Optimal change heuristic: Wallets do not spend unnecessary outputs. This means that a transaction with say 2 inputs of 0.5 each and 2 outputs of 0.6 and 0.4, the 0.4 is assumed to be the change address belonging to the same wallet. This is because if the intended payment is 0.4, the wallet would have chosen a single 0.5 input.
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  • The question is asking about a method to quantify how closely related two addresses are. Your answer is related to the topic, but doesn't address the question. If it is answered in the video, please include the relevant points in your answer. Otherwise, I think this post is to be classified as "not an answer" on this question.
    – Murch ♦
    Apr 29, 2016 at 8:23
  • Sure, I'll edit the response to answer the question.
    – mrkent
    May 9, 2016 at 18:25
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To quantitify user privacy there is the Bitcoin privacy score which is available for all BTC addresses which were ever used in the blockchain. It's a score between 0% and 100%. Close to 100% means excellent privacy:

  • No address re-use
  • several analytical heuristics to group the address with others belonging with high likelihood to the same entity (co-spend ...) not successful
  • No path to one of the millions of known exchange addresses (deposits)
  • No path from an exchange address to the subject address (withdrawal)

The lower the score the worse the privacy of the bitcoin address. If you want to try it out here the link: Bitcoin privacy score
(Disclosure: As co-programmer I'm affiliated to the btctester site)

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    It looks like you are affiliated with the site that you link to. Please disclose that you are affiliated with the website in answers where you do link it. As our site rules (bitcoin.stackexchange.com/help/promotion) state "you must disclose your affiliation in your answers." Otherwise your posts may be removed as spam.
    – Andrew Chow ♦
    Nov 16, 2020 at 18:55
  • I understand and was not aware, thanks for information and apologies! I edited and added a disclosure statement.
    – tempo
    Nov 17, 2020 at 22:55

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