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EIP-1108: Reduce alt bn128 gas costs #1108

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EIP-1108: Reduce alt bn128 gas costs #1108

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dd9f6be
Add draft of elliptic-curve gas cost reduction EIP
Shadowfiend May 21, 2018
21e3f06
Add status and EIP dependencies
Shadowfiend May 21, 2018
d1aafab
Lowercase preamble per observed practice
Shadowfiend May 21, 2018
d8eaa3e
Tweak EIP title to reflect core cause for cost reduction
Shadowfiend May 21, 2018
1311b36
Reduce constant factor in line with original EIP issue
Shadowfiend May 22, 2018
9fd2cd1
Fix footnote formatting
Shadowfiend May 22, 2018
4ef1d40
Drop extraneous code fence
Shadowfiend May 23, 2018
1a97a7b
GitHub username only for EIP author line
Shadowfiend May 23, 2018
40e45ab
Label alt_bn128 gas cost EIP as EIP 1108
Shadowfiend May 23, 2018
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50 changes: 50 additions & 0 deletions EIPS/eip-reduce-alt_bn128-gas-costs.md
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---
```
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Please remove the backticks here to comply with the standard formatting.

eip: <to be assigned>
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Please rename to eip-1108.md and number 1108.

title: Reduce alt_bn128 precompile gas costs
author: Antonio Salazar Cardozo (@shadowfiend) <antonio@keep.network>
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Please supply either github username or email, not both.

status: Draft
type: Standards Track
category: Core
created: 2018-05-21
requires: 196, 197
```
---

## Short Description

Recent changes to the underlying library used by the official Go reference
implementation led to significant performance gains for the `ECADD`, `ECMUL`,
and pairing check precompiled contracts on the `alt_bn128` elliptic curve, which
should be reflected in reduced gas costs.

## Motivation

Recently, the underlying library used by the [official Go reference
implementation](https://github.com/ethereum/go-ethereum) to implement the
`ECADD` (at address `0x06`), `ECMUL` (at address `0x07`), and pairing check (at
address `0x08`) precompiled contracts was shifted to [Cloudflare's bn256
library](https://github.com/cloudflare/bn256). Based on the [initial PR that
introduced this change](https://github.com/ethereum/go-ethereum/pull/16203),
and corroborated in [a later
note](https://github.com/ethereum/go-ethereum/pull/16301#issuecomment-372687543),
the computational cost of `ECADD`, `ECMUL`, and pairing checks (excepting the
constant) has dropped roughly an order of magnitude across the board.

## Specification

Following is a table with the current gas cost and new gas cost:

| Contract | Address | Current Gas Cost | Updated Gas Cost |
| ------------- | --------- | ----------------------------- | ------------------- |
| `ECADD` | `0x06` | 500<sup>[1]</sup> | 50 |
| `ECMUL` | `0x07` | 40 000<sup>[1]</sup> | 2 000 |
| Pairing check | `0x08` | 80 000k + 100 000<sup>[2]</sup>| 5 500k + 80 000 |

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.

[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).