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nip45: negate pow attacks on hyperloglog using a stupid hack.

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fiatjaf 2024-11-03 16:49:02 -03:00
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@ -41,13 +41,14 @@ This is so it enables merging results from multiple relays and yielding a reason
### Algorithm
The HLL value must be calculated with a precision of `8`, i.e. with 256 registers.
This section describes the steps a relay should take in order to return HLL values to clients.
To compute HLL values, first initi the 256 registers to `0` each; then, for on every event to be counted,
1. take byte `16` of the `id` and use it to determine the register index;
2. count the number of leading zero bits in the following bytes `17..24` of the `id`;
3. if the number of leading zeros is bigger than what was previously stored in that register, overwrite it.
1. Upon receiving a filter, if it has a single `#e`, `#p`, `#a` or `#q` item, read its 32th ascii character as a byte and take its modulo over 24 to obtain an `offset` -- in the unlikely case that the filter doesn't meet these conditions, set `offset` to the number 16;
2. Initialize 256 registers to 0 for the HLL value;
3. For all the events that are to be counted according to the filter, do this:
1. Read byte at position `offset` of the event `pubkey`, its value will be the register index `ri`;
2. Count the number of leading zero bits starting at position `offset+1` of the event `pubkey`;
3. Compare that with the value stored at register `ri`, if the new number is bigger, store it.
That is all that has to be done on the relay side, and therefore the only part needed for interoperability.