Early ASIC Mitigation Hardfork

EIPS/eip-X-ASIC-resistant-block-mining.md

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+---
+eip: <to be assigned>
+title: Poisoning the Well
+author: David Stanfill <david@airsquirrels.com> 
+discussions-to: <email address>
+status: Draft
+type: Standards Track
+category Core
+created: 2018-04-03
+---
+
+
+## Simple Summary
+
+This EIP attempts to break ASIC miners specialized for the current ethash
+mining algorithm.
+
+
+## Abstract
+
+There are companies who currently have dedicated hardware based ethereum miners in
+production, and may be actively mining.  This EIP aims to "poison
+the well" by modifying the block mining algorithm in a low risk manner that
+may *"break"* these miners if they are in-fact built as traditional ASICs.
+
+
+## Motivation
+
+ASIC based miners will have lower operational costs than GPU based miners which
+will result in GPU based mining quickly becoming unprofitable.  Given that
+production of ASIC based miners has a high barrier to entry and few market players,
+this will cause a trend towards centralization of mining power.  
+
+This trend towards centralization has a negative effect on network security,
+putting significant control of the network in the hands of only a few entities.
+
+Ethash remains ASIC resistant, however ASIC manufacturer technology is advancing
+and ethash may require further changes in order to remain resistant to unforeseen
+design techniques. This EIP seeks explicitly to buy time during which newly developed
+ASIC technology will face a barrier while more long term mechanisms to ensure 
+continued ASIC resistance can be explored.  
+
+## Specification
+
+If `block.number >= ASIC_MITIGATION_FORK_BLKNUM`, require that the ethash solution 
+sealing the block has been mined using `ethashV2`.
+
+## EthashV2
+
+`ethashV2` will be identical in specification to the current `ethash`(v1) algorithm, with
+the exception of the implementation of `fnv`. 
+
+The new algorithm replaces the 5 current uses of `fnv` inside `hashimoto` with 5 
+seperate instances defined as `fnvA`, `fnvB`, `fnvC`, `fnvD`, and `fnvE`, utilizing 
+
+`FNV_PRIME_A=0x10001a7`  
+`FNV_PRIME_B=0x10001ab`  
+`FNV_PRIME_C=0x10001cf`  
+`FNV_PRIME_D=0x10001e3`  
+`FNV_PRIME_E=0x10001f9`  
+
+
+`fnvA` replaces `fnv` in the DAG item selection step
+`fnvB` replaces `fnv` in the DAG item mix step
+`fnvC(fnvD(fnvE` replaces `fnv(fnv(fnv(` in the compress mix step
+
+`fnv` as utilized in DAG-item creation should remain unchanged.
+
+## Node Changes (Optional Variant)
+
+A new field of `EthashVersion` defined as an 8 bit unsigned enumeration is added to 
+the the block header. If this field is absent, its value is assumed to be equal to
+ zero.
+
+The enumeration should be forward compatible and defined as:
+`EthashUndefined = 0x00  
+EthashVersion1 = 0x01  
+EthashVersion2 = 0x02  
+...  
+EthashVersion255 = 0xFF`
+
+When this field is present and set to 0x02, the `mine` and `VerifySeal` operations
+utilize the `ethashV2` algorithm. If this field is set to any value other than 0x01,
+0x02, or 0x00 `VerifySeal` shall reject the block.
+
+`VerifySeal` shall also fail verification in the event 
+`block.Number >= ASIC_MITIGATION_FORK_BLKNUM && block.EthashVersion < EthashVersion2`
+
+## Agent Changes (Optional Variant, stand alone or combined with Node Changes)
+
+GetWork may optionally return the proposed blocks `EthashVersion` field. While a 
+miner or pool may infer the requirement for ethashV2 based on the computed 
+epoch of the provided seedHash, it may be beneficial to explicitly provide this
+field so a miner does not require special configuration when mining on a chain
+that chooses not to implement the ASIC_Mitigation hardfork.
+
+Due to compatibility concerns with implementations that already add additional 
+parameters to GetWork, it may be desired to define a 33 Byte BlockHeader, where
+the first octet represents the EthashVersion enumeration value required for the 
+block. If this octet is not present, it may be assumed to be zero.
+
+## Rationale
+
+This EIP is aimed at breaking existing ASIC based miners via small changes to the
+existing ethash algorithm.  We hope to accomplish the following:
+
+1. Break existing ASIC based miners.
+2. Demonstrate a willingness to fork in the event of future ASIC miner production.
+
+Goal #1 is something that we can only do probabalistically without detailed
+knowledge of existing ASIC miner design.  Our approach should balance the
+inherent security risks involved with changing the mining algorithm with the
+risk that the change we make does not break existing ASIC miners.  This EIP
+leans towards minimizing the security risks by making minimal changes to the
+algorithm accepting the risk that the change may not break dedicated hardware 
+miners that utilize partially or fully configurable logic. 
+
+Furthermore, we do not wish to introduce significant algorithm changes that
+may alter the power utilization or performance profile of existing GPU hardware.
+
+The change of FNV constant is a minimal change that can be quickly
+implemented across the various network node and miner implementations.
+
+It is proposed that `ASIC_MITIGATION_FORK_BLKNUM` be no more than 5550000 (epoch 185), giving
+around 30 days of notice to node and miner developers and a sufficient window
+for formal analysis of the changes by experts. We must weigh this window against
+the risk introduced by allowing ASICs that may exist to continue to propagate
+on the network, as well as the risk of providing too much advanced warning to 
+ASIC developers. 
+
+It is further understood that this change will not prevent redesign of existing
+dedicated hardware with new ASIC chips. The intention of this change is only
+to disable currently active or mid-production hardware and provide time for
+POS development as well as larger algorithim changes to be well analyzed by 
+experts.
+
+The choice of FNV constants is made based on the formal specification at
+https://tools.ietf.org/html/draft-eastlake-fnv-14#section-2.1
+
+Typical ASIC synthesis tools would optimize multiplication of a constant
+in the FNV algorithm, reducing the area needed for the multiplier according
+to the hamming weight of the constant. To reduce the chance of ASIC adaptation
+through minor mask changes, we propose choosing new constants with a larger
+hamming weight, however care should be taken not to choose constants with too
+large of weight.
+
+The current FNV prime, 0x1000193 has a hamming weight of 6.   
+`HammingWeight(0x10001a7) = 7;`  
+`HammingWeight(0x10001ab) = 7;`    
+`HammingWeight(0x10001cf) = 8;`    
+`HammingWeight(0x10001e3) = 7;`    
+`HammingWeight(0x10001ef) = 9; // Not chosen`   
+`HammingWeight(0x10001f9) = 8;`  
+`HammingWeight(0x10001fb) = 9; // Not chosen`
+
+An exhaustive analysis was done regarding the dispersion of these constants as compared to 0x01000193.
+
+It can be empirically confirmed that no more than 1 duplicates occur in the 32 bit word space with these constants. 
+
+It is worth noting that FNV is not a cryptographic hash, and it is not used as such in ethash. With 
+that said, a more invasive hash algorithm change could consider other options. One suggestion has been 
+MurmorHash3 (https://github.com/aappleby/smhasher/blob/master/src/MurmurHash3.cpp)
+
+## Backwards Compatibility
+
+This change implements a backwards incompatable change to proof of work based
+block mining.  All existing miners will be required to update to clients which
+implement this new algorithm, and all nodes will require updates to accept
+solutions from the new proof of work algorithm.
+
+## Test Cases
+
+TODO: will need to generate test cases for `ethereum/tests` repository corresponding to the consensus 
+changes.
+
+## Implementation
+
+TODO
+
+## Copyright
+
+Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).