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"Peter Todd" <pete@petertodd.org>
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Subject: Re: [Bitcoin-development] Privacy and blockchain data
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>
> 2) Common prefixes: Generate addresses such that for a given wallet they
> all share a fixed prefix. The length of that prefix determines the
> anonymity set and associated privacy/bandwidth tradeoff, which
> remainds a fixed ratio of all transactions for the life of the
> wallet.
>
Interesting thought to make the privacy/bandwidth trade-off using
vanitygen and prefix filters.
But doesn't this effectively expand the universe of potential spies from
'the global attacker' who is watching your SPV queries, to simply 'the
globe' -- anyone with a copy of the blockchain?
Some stats on UTXO set size: (slightly stale -- as of block 270733)
7.4m unspent outputs
2.2m transactions with unspent outputs
2.1m unique unspent scriptPubKeys
Side note: the top 1,000 scriptPubKeys have 10% of all unspent outputs.
Let's say you use an 8-bit prefix (1/256) that would be ~10,000
transactions in the UTXO you would be monitoring. But if I knew a few
different days / time-periods you transacted, I could figure out your
prefix.
Of course, anyone you transact with would know your prefix outright.
Wouldn't this also allow obvious identification of spend versus change
addresses in a transaction?
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