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EIP-1108: Add gas cost clarification + copyright assignment #2067

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May 24, 2019
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EIP-1108: Add gas cost clarification + copyright assignment #2067

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Added copyright CC0 assignment
Shadowfiend May 23, 2019
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Expand on gas cost justification for EIP-1108
Shadowfiend May 23, 2019
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Merge remote-tracking branch 'ethereum/master' into HEAD
axic May 24, 2019
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20 changes: 19 additions & 1 deletion EIPS/eip-1108.md
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Expand Up @@ -59,14 +59,28 @@ Following is a table with the current gas cost and new gas cost:
The gas costs for `ECADD` and `ECMUL` are updates to the costs listed in
EIP-196, while the gas costs for the pairing check are updates to the cost
listed in EIP-197. Updated gas costs have been adjusted to the less performant
client which is Parity, according to benchmarks<sup>[3]</sup>. The updated gas costs are scaled relative to the `ecrecover` precompile. i.e. in the benchmark, `ecrecover` ran in 116 microseconds. If we consider 3,000 gas the fair price for `ecrecover`, we can obtain a metric how much gas should be charged per microsecond of an algorithm's runtime, and use that to price the elliptic curve precompiles.
client which is Parity, according to benchmarks<sup>[3]</sup>.

To come up with these updates gas costs, the performance of the `ecrecover` precompile
was measured at 116 microseconds per `ecrecover` invocation. Assuming the `ecrecover`
gas price is fair at 3,000 gas, we get a price of 25.86 gas per microsecond of a precompile
algorithm's runtime. With this in mind, the pairing precompile took 3,037 microseconds to
compute 1 pairing, and 14,663 microseconds to compute 10 pairings. From this, the pairing
algorithm has a fixed 'base' run-time of 1,745 microseconds, plus 1,292 microseconds per
pairing. We can split the run-time into 'fixed cost' and 'linear cost per pairing'
components because of the structure of the algorithm.

Thus using a 'fair' price of 25.86 gas per microsecond, we get a gas formula of
~`35,000 * k + 45,000` gas, where `k` is the number of pairings being computed. [4]

[1]- Per [EIP-196](https://github.com/ethereum/EIPs/blob/984cf5de90bbf5fbe7e49be227b0c2f9567e661e/EIPS/eip-196.md#gas-costs).

[2]- Per [EIP-197](https://github.com/ethereum/EIPs/blob/df132cd37efb3986f9cd3ef4922b15a767d2c54a/EIPS/eip-197.md#specification).

[3]- [Parity benchmarks.](https://gist.github.com/zac-williamson/838410a3da179d47d31b25b586c15e53)

[4]- [PR comment clarifying gas cost math](https://github.com/ethereum/EIPs/pull/1987#discussion_r280977066).

## Rationale

### Existing protocols would benefit immensely from cheaper elliptic curve cryptography
Expand Down Expand Up @@ -116,3 +130,7 @@ Both the Parity and Geth clients have already implemented cryptographic librarie
* [Geth bn256 library (golang)](https://github.com/ethereum/go-ethereum/tree/master/crypto/bn256/cloudflare)
* [MCL, a portable C++ pairing library](https://github.com/herumi/mcl)
* [Libff, a C++ pairing library used in many zk-SNARK libraries](https://github.com/scipr-lab/libff)


## Copyright
Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).