How to shorten UUID V4 without making it non-unique/guessable

Question

I have to generate unique URL part which will be "unguessable" and "resistant" to brute force attack. It also has to be as short as possible :) and all generated values has to be of same length. I was thinking about using UUID V4 which can be represented by 32 (without hyphens) hex chars de305d5475b4431badb2eb6b9e546014 but it's a bit too long. So my question is how to generate something unqiue, that can be represented with url charcters with same length for each generated value and shorter than 32 chars. (In node.js or pgpsql)

Answer 1

v4() will generate a large number which is translated into a hexadecimal string. In Node.js you can use Buffer to convert the string into a smaller base64 encoding:

import { v4 } from 'uuid';

function getRandomName() {

    let hexString = v4();
    console.log("hex:   ", hexString);
    
    // remove decoration
    hexString = hexString.replace(/-/g, "");
    
    let base64String = Buffer.from(hexString, 'hex').toString('base64')
    console.log("base64:", base64String);
    
    return base64String;
}

Which produces:

hex:    6fa1ca99-a92b-4d2a-aac2-7c7977119ebc
base64: b6HKmakr

hex:    bd23c8fd-0f62-49f4-9e51-8b5c97601a16
base64: vSPI/Q9i

Answer 2

UUID v4 itself does not actually guarantee uniqueness. It's just very, very unlikely that two randomly generated UUIDs will clash. That's why they need to be so long - that reduces the clashing chance. So you can make it shorter, but the shorter you make it, the more likely that it won't actually be unique. UUID v4 is 128 bit long because that is commonly considered "unique enough".