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Mix the mixin

dnaleor posted this 8 years ago

dnaleor | 8 years ago

Hi guys,

I just had this thought:

The mixin number is public, and AFAIK even CT won't conceal this. People are able to set the mixin themselves. When someone uses mixin for example "23" by default, this is a risk: It's a number that will not be used much, so all the transactions can potentially be grouped together.

How?

A merchant or exhcnage received a transaction with mixin 23. He checks the blockchain and sees a bunch of those transactions with that strange mixin number, so he can get a bit of info from it.

I know we are already protected by stealth addresses and ring sigs (and maybe CT in the future), but I think it would be a good approach to also "mix the mixin".

How?

Well, the GUI could have 3 levels for mixin, for example "low", "medium" and "high" and the option to customize it (for experienced users only)

When people select "low" they will use a mixin number randomly chosen between (for example) 3 and 6

When people select "medium" they will use a mixin number randomly chosen between (for example) 7 and 14

When people select "high" they will use a mixin number randomly chosen between (for example) 15 and 30

People can still can select "customize mixin" and even put in a number higher than 30...

This will at least lead to the mixin numbers between 3 and 30 being used very often, so these numbers can be picked without worrying.

Replies: 3
luigi1111 posted 8 years ago Replies: 1 | Weight: -129 | Link [ - ]

Hmmm....

  1. With more usage it becomes increasingly irrelevant (small possible number of mixins vs large number of participants)
  2. If you are worried about someone correlating your "odd" mixin amount, simply do not use an odd amount. I think "noobs" are more likely to use the default than to choose some random number without understanding.
  3. Low, Medium, High examples are too high (probably subjective). Transactions start getting large pretty quickly (mixin * inputs).

With that said, I'm not necessarily against this proposal with different numbers (say 3-4, 5-7, 8-10 or something). It's just a wallet configuration after all. :) Maybe the "low" one shouldn't be variable, so you don't randomly pay a bit more fee than you "should" for routine transactions.

Reply to: luigi1111
dnaleor posted 8 years ago Replies: 1 | Weight: -129 | Link [ - ]

"If you are worried about someone correlating your "odd" mixin amount, simply do not use an odd amount."

Exactly this reasoning will make people to gravitate towards using the same mixing (or maybe just a few numbers, for example 3, 5 and 10), making it even more risky to use 8.

If people want to use a high number, they should be able to do that, so certainly for the higher numbers I would suggest a random number.

about the numbers:

IIRC, there was talk to raise the minimum to 5 in stead of 3.

I agree that the lowest should maybe be "fixed". Maybe something like this could word:

  • LOW: mixin 5
  • MEDIUM: 6-7
  • HIGH: 8-10
  • EXTREME: 11-100
Reply to: dnaleor luigi1111
luigi1111 posted 8 years ago Weight: -129 | Link [ - ]

I can't possibly see 8 as risky under my 1. above, but with that said, I don't really get why we should "support" users' (conjectured) odd mixin habits. If you're really worried about privacy, why wouldn't you use 10 (or 15, or 20) instead of 23?

Anyway, I feel argumentative today. :)

I think the current default is planning to be 4, not 5, but if you adjust that schedule down 1 or whatever then no biggie, apart from the EXTREME category, which I wouldn't support.