IPFS CID Storage Analysis

This code was forked from here. An additional and more efficient method was added.

In this analysis the different methods of storing an IPFS CID on the Ethereum blockchain is investigated and the network fees (gas cost) are analysed.

The analogy of an IPFS CID multihash is defined as follows:

For more information please read this.

The fn code defines which hash-function is used. The complete table for all fn code can be found here.

Findings

The goal of each method is to store an IPFS multihash on the Ethereum blockchain. For this analysis, the following CID is used:

const cid = "QmWATWQ7fVPP2EFGu71UkfnqhYXDYH566qy47CnJDgvs8u";

Furthermore, it is asumed that one unit of gas costs:

gasPrice: 20000000000

Stroing CID as String

string hash;
function storeCIDAsString(string memory _hash) public {
    hash = _hash;
}

gasUsed: 86163 units
gasCost (ether): 0.00172326 ether

Stroing CID as Struct

struct Multihash {
    bytes2 hash_function;
    uint8 size;
    bytes32 hash;
}

Multihash multihash;

function storeCIDAsStruct(bytes2 _hash_function, uint8 _size, bytes32 _hash) public{
    multihash = Multihash(_hash_function, _size, _hash);
}

gasUsed: 69848 units
gasCost (ether): 0.00139696 ether

Stroing CID as String in logs

event CIDStoredInTheLog(string _hash);

function storeCIDInTheLog(string memory _hash) public {
    emit CIDStoredInTheLog(_hash);
}

gasUsed: 27675 units
gasCost (ether): 0.0005535 ether

Stroing CID as a Struct in logs

event CIDStructStoredInTheLog(
    bytes1 hash_function,
    bytes1 size,
    bytes32 hash
);

function storeCIDStructInTheLog(
    bytes1 _hash_function,
    bytes1 _size,
    bytes32 _hash
) public {
    emit CIDStructStoredInTheLog(_hash_function, _size, _hash);
}

gasUsed: 25841 units
gasCost (ether): 0.00051682 ether

Conclusion

As shown in these examples, the gas prices can be greatly reduced when storing an IPFS CID in the logs with data types of distinct length.

25841 / 86163 < 0.3

So in average more than 70% of gas can be saved.

Installation

Prerequisites

Git command line interface
Node.js command line interface
Ganache to spin up a blockchain with funded test accounts and instant mining

Setup

Clone the repo:

git clone https://github.com/bc-ticketing/ipfs-multihash-analysis
cd ipfs-multihash-analysis

Install Truffle

sudo npm install -g truffle

Run the tests

npm install
npm test