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@ -95,5 +95,42 @@ These RPCs interact with zaddr xtns and may report different or additional info |
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listunspent |
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``` |
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### z\_sendmany |
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### z\_sendmany Rule of Seven |
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Our goal is to be non-deterministic while also inserting enough zouts such that we have at least N=7 zouts. |
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Since the normal case is to have 2 zouts (one recipient for a z2z and one change zout back to sending address), |
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the normal case will be to add 5 zouts to a normal z2z xtn. |
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For a z=>t, we must add .... |
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For a t=>z we must add 6. |
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The reason N=7 is chosen is because of the simple fact that `6!=720` while `7!=5040`. This parameter is chosen |
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in response to the ITM attack, which relies on a small number of zouts and doing combinatorial algorithms on all |
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possibilities. These combinatorial algorithms increase in state space for each link in a long chain of transactions. |
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Traditionally each xtn only has a few zouts and so because `2!=2` and `3!=6`, the combinatorial explosion does not |
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have a chance to slow down the ITM attack. |
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Now, consider 5040 choices at each link in a chain, and say we are studying a chain of length L=10. |
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Compared to pre-Sietch, we would have `2^10=1024` possibilities versus |
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``` |
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5040^10 = 10575608481180064985917685760000000000 |
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```` |
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possibilities. Even for short chains of xtns, the combinatorial explosion of possibility renders the ITM attack |
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extremely expensive. It limits it to searching for linkability metadata in only short chains with lots of |
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additional supporting metadata, effectively raising the bar for attack and removing many potential attackers |
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who do not have sufficient resources. In pre-Sietch code, the ITM attack can potentially research very long chains, |
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dozens, hundreds and perhaps thousands of transactions in length, with commodity hardware. |
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Sietch exponenentially increases the cost of doing this, in RAM, CPU and running-time. |
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### Non-determinism |
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Combinatorial explosion can only protect us so much. It is only one layer of defense. |
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When adding zutxos, to break the ITM/Metaverse metadata attacks at a deep level, we much break a deep assumption |
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that is baked deep into Bitcoin: determinism. |
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