estimate-collisions.js

const { createHash } = require('crypto');

const hashFunction = 'sha256';
const hashDigest = 'base64';
const hashDigestLength = 5;

function currentImplementation(content, hashSalt) {
    const hash = createHash(hashFunction);
    if (hashSalt) {
        hash.update(hashSalt);
    }
    hash.update(content);
    const localIdentHash = hash
        .digest(hashDigest)
        .slice(0, hashDigestLength)
        .replace(/[/+]/g, "_")
        .replace(/^\d/g, "_")
    ;
    return localIdentHash;
}

function proprosedImplementation(content, hashSalt) {
    let localIdentHash = '';
    for (const tierSalt = Uint32Array.of(0); localIdentHash.length < hashDigestLength; tierSalt[0]++) {
        const hash = createHash(hashFunction);
        if (hashSalt) {
            hash.update(hashSalt);
        }
        hash.update(tierSalt);
        hash.update(content);
        localIdentHash = (localIdentHash + hash.digest(hashDigest))
            .replace(/^\d+/, "")
            .slice(0, hashDigestLength)
            .replace(/[/]/g, "_")
            .replace(/[+]/g, "-")
        ;
    }
    return localIdentHash;
}


function hashesUntilCollision(hasher, salt) {
    const set = new Set();
    for (let i = 1; ; i++) {
        const localIdHash = hasher(`Some string used as content #${i}`, salt);
        if (set.has(localIdHash)) {
            return i;
        }
        set.add(localIdHash);
    }
}

function medianHashesUntilCollision(hasher) {
    let results = [];
    for (let i = 0; i < 101; i++) {
        results.push(hashesUntilCollision(hasher, String(i)));
    }
    results.sort((a, b) => a - b);
    return results[Math.floor(results.length / 2)];
}

console.log('Current', medianHashesUntilCollision(currentImplementation));
console.log('Proposed', medianHashesUntilCollision(proprosedImplementation));