CODEWITHSUNDEEP
php
Billy Bones
Billy Bones

Reputation: 2975

High Entropy Unique ID for Filenames

I would like to create a unique ID (filename) for some of my files and would like to do so with minimal concern. My original plan was to use a base64 encoded string of random bytes but this will not work because / is a valid base64 character.

The function I currently use looks like this:

static function uniqueID(){
    return base64_encode(random_bytes(16));
}

How could I go about generating a high entropy unique ID that will always be a certain length and contain only characters that are valid in filenames?

Note: I do not wish to use a solution that accomplishes this with str_replace().

Edit: I appreciate the responses so far.This is one solution Ive explored locally but I am not sure how to calculate how much entropy I lose when compared to uniqueID().

public static function uniqueFilename(){
    return bin2hex(random_bytes(12));
}

Upvotes: 1

Views: 308

Answers (2)

Billy Bones
Billy Bones

Reputation: 2975

As User: Sammitch stated,

12 bytes = 96 bits. If you generated a random 96-bit value and then tried to intentionally brute-force guess a collision you'd need to build a Dyson sphere around the sun to power the computer and then wait a few centuries. Just use the random bytes.

96 bits is like concatenating 3x 32bit numbers together, the number of possibilities is: 79,228,162,514,264,337,593,543,950,336

Knowing this we can justify using the following function when $n >= 12.

public static function uniqueFilename($n = 12){
    return bin2hex(random_bytes($n));
}

Upvotes: 1

adrian7
adrian7

Reputation: 1016

I would recommend Ramsey's UUID: https://github.com/ramsey/uuid .
We use it in production and it does the job.

Upvotes: 0

Related Questions