mirror of https://github.com/status-im/EIPs.git
235 lines
9.1 KiB
Markdown
235 lines
9.1 KiB
Markdown
---
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eip: 969
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title: Modifications to ethash to invalidate existing dedicated hardware implementations
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author: David Stanfill <david@airsquirrels.com>
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discussions-to: https://gitter.im/ethereum/topics/topic/5ac4d974109bb043328911ce/eip-969-discussion
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status: Draft
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type: Standards Track
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category: Core
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created: 2018-04-03
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---
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## Simple Summary
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This EIP modifies ethash in order to break ASIC miners specialized for the current ethash
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mining algorithm.
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## Abstract
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There are companies who currently have dedicated hardware based ethereum miners in
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production, and may be actively mining. This EIP aims to "poison
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the well" by modifying the block mining algorithm in a low risk manner that
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may *"break"* these miners if they are in-fact built as traditional ASICs.
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## Motivation
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ASIC-based miners will have lower operational costs than GPU-based miners, which
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will result in GPU-based mining quickly becoming unprofitable. Given that
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production of ASIC-based miners has a high barrier to entry and few market players,
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this will cause a trend towards centralization of mining power.
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Risks include market dominance by a single manufacturer that may utilize production
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stock to mine themselves, introduce backdoors in their hardware, or facilitate a 51%
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attack that would otherwise be infeasible.
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This trend towards centralization has a negative effect on network security,
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putting significant control of the network in the hands of only a few entities.
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Ethash remains ASIC-resistant, however ASIC manufacturer technology is advancing
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and ethash may require further changes in order to remain resistant to unforeseen
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design techniques. This EIP seeks explicitly to buy time during which newly-developed
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ASIC technology will face a barrier while more long-term mechanisms to ensure
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continued ASIC resistance can be explored.
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## Specification
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If `block.number >= ASIC_MITIGATION_FORK_BLKNUM`, require that the ethash solution
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sealing the block has been mined using `ethashV2`.
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## EthashV2
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`ethashV2` will be identical in specification to the current `ethash`(v1) algorithm, with
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the exception of the implementation of `fnv`.
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The new algorithm replaces the 5 current uses of `fnv` inside `hashimoto` with 5
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separate instances defined as `fnvA`, `fnvB`, `fnvC`, `fnvD`, and `fnvE`, utilizing
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``` c
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FNV_PRIME_A=0x10001a7
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FNV_PRIME_B=0x10001ab
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FNV_PRIME_C=0x10001cf
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FNV_PRIME_D=0x10001e3
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FNV_PRIME_E=0x10001f9
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```
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`fnvA` replaces `fnv` in the DAG item selection step;
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`fnvB` replaces `fnv` in the DAG item mix step;
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`fnvC(fnvD(fnvE` replaces `fnv(fnv(fnv(` in the compress mix step.
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`fnv` as utilized in DAG-item creation should remain unchanged.
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## Agent Changes (Optional Variant)
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The JSON-RPC `eth_GetWork` call may optionally return the proposed blocks algorithm.
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While a miner or pool may infer the requirement for `ethashV2` based on the computed
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epoch of the provided seedHash, it is beneficial to explicitly provide this
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field so a miner does not require special configuration when mining on a chain
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that chooses not to implement the `ASIC_Mitigation` hardfork.
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Due to compatibility concerns with implementations that already add additional
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parameters to `GetWork`, it is desired to add `BlockNumber` as an explicit 4th parameter
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as suggested in https://github.com/ethereum/go-ethereum/issues/2333. Algorithm
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should then be returned as either `"ethash"` or `"ethashV2"` according to the
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`block.number >= ASIC_MITIGATION_FORK_BLKNUM` criteria.
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## Rationale
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This EIP is aimed at breaking existing ASIC-based miners via small changes to the
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existing ethash algorithm. We hope to accomplish the following:
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1. Break existing ASIC-based miners.
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2. Demonstrate a willingness to fork in the event of future ASIC miner production.
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Goal #1 is something that we can only do probabilistically without detailed
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knowledge of existing ASIC miner design. The known released miner is available for
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purchase [here](https://shop.bitmain.com/product/detail?pid=00020180403174908564M8dMJKtz06B7),
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with delivery slated for mid-summer 2018.
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Our approach should balance the inherent security risks involved with changing
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the mining algorithm with the risk that the change we make does not break existing
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ASIC miners. This EIP leans towards minimizing the security risks by making minimal
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changes to the algorithm, accepting the risk that the change may not break dedicated
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hardware miners that utilize partially- or fully-configurable logic.
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Furthermore, we do not wish to introduce significant algorithm changes that
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may alter the power utilization or performance profile of existing GPU hardware.
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The change of FNV constant is a minimal change that can be quickly
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implemented across the various network node and miner implementations.
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It is proposed that `ASIC_MITIGATION_FORK_BLKNUM` be no more than 5550000 (epoch 185), giving
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around 30 days of notice to node and miner developers and a sufficient window
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for formal analysis of the changes by experts. We must weigh this window against
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the risk introduced by allowing ASICs that may exist to continue to propagate
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on the network, as well as the risk of providing too much advanced warning to
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ASIC developers.
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It is further understood that this change will not prevent redesign of existing
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dedicated hardware with new ASIC chips. The intention of this change is only
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to disable currently active or mid-production hardware and provide time for
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POS development as well as larger algorithim changes to be well analyzed by
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experts.
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The choice of FNV constants is made based on the formal specification at
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https://tools.ietf.org/html/draft-eastlake-fnv-14#section-2.1
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@goobur provided the following python code to output primes matching this criteria:
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``` python
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candidates = [2**24 + 2**8 + _ for _ in xrange(256)]
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candidates = [_ for _ in candidates if is_prime(_)]
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["0x%x" % _ for _ in candidates if _ % (2**40 - 2**24 - 1) > (2**24 + 2**8 + 2**7)]
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```
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The minimal prime constraint was relaxed, as has already been the case in `ethashV1`.
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Typical ASIC synthesis tools would optimize multiplication of a constant
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in the FNV algorithm, while reducing the area needed for the multiplier according
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to the hamming weight of the constant. To reduce the chance of ASIC adaptation
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through minor mask changes, we propose choosing new constants with a larger
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hamming weight, however care should be taken not to choose constants with too
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large of a weight.
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The current FNV prime, `0x1000193`, has a hamming weight of 6.
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``` c
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HammingWeight(0x10001a7) = 7;
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HammingWeight(0x10001ab) = 7;
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HammingWeight(0x10001cf) = 8;
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HammingWeight(0x10001e3) = 7;
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HammingWeight(0x10001ef) = 9; // Not chosen
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HammingWeight(0x10001f9) = 8;
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HammingWeight(0x10001fb) = 9; // Not chosen
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```
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An analysis can be done regarding the dispersion of these constants as compared to
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`0x01000193`, using the following snippet.
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``` c
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// https://eips.ethereum.org/EIPS/eip-969
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#include <stdlib.h>
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#include <stdio.h>
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#include <string.h>
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int main() {
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u_int32_t candidate = 0;
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u_int32_t dups = 0;
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u_int32_t fnv_candidate = 0x10001a7; // MODIFY!
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u_int8_t *counts = malloc(0xFFFFFFFF);
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memset(counts, '\0', 0xFFFFFFFF);
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for (candidate = 0; candidate < 0xFFFFFFFF; candidate++) {
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u_int32_t result = (u_int32_t)(candidate * fnv_candidate);
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u_int8_t oldCount = counts[result];
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counts[result] = counts[result]+1;
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if (oldCount != 0) {
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dups++;
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}
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//// progress display: remove comment to speed down
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//if ((candidate & 0xFFFFF) == 0xFFFFF) printf("0x%08x\n", candidate);
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}
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printf("\nFNV candidate 0x%08x : %i dups\n", fnv_candidate, dups);
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return 0;
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}
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```
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It can be empirically confirmed that no more than 1 duplicate occurs in the
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32-bit word space with these constants.
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It is worth noting that FNV is not a cryptographic hash, and it is not used as
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such in ethash. That said, a more invasive hash algorithm change could be considered.
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One suggestion has been [MurmurHash3](https://github.com/aappleby/smhasher/blob/master/src/MurmurHash3.cpp).
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[Other suggestions have been made](https://twitter.com/el33th4xor/status/981292363627810818):
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[Argon2](https://github.com/P-H-C/phc-winner-argon2),
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[Equihash](https://blog.z.cash/why-equihash/) of Zcash fame, and
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[Balloon Hashing](https://crypto.stanford.edu/balloon/).
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Another possible candidate is [Cuckoo Cycle](https://github.com/tromp/cuckoo),
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although there are some concerns regarding unaddressed optimization
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vulnerabilities. One review can be found
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[here](https://da-data.blogspot.com/2014/03/a-public-review-of-cuckoo-cycle.html).
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This may be considered once the exact mechanism of the released ASICs is known and
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their effectiveness against its optimisations can be fully evaluated.
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## Backwards Compatibility
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This change implements a backwards incompatible change to proof of work based
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block mining. All existing miners will be required to update to clients which
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implement this new algorithm, and all nodes will require updates to accept
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solutions from the new proof of work algorithm.
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## Test Cases
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TODO: will need to generate test cases for `ethereum/tests` repository corresponding to the consensus
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changes.
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## Implementation
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TODO
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## Copyright
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Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).
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