How do uuids work

Show 3 more comments. But only after using up exabytes of storage for those IDs. Is the uniqueness purely because of randomness?

Or there are other factors? TheTahaan That's not what random means. It doesn't mean "totally unpredictable" -- usually they follow some kind of distribution. It's truly random, but we absolutely can know the chance of getting a particular outcome. We just can't say in advance whether it will happen.

Just to explain what this implementation did wrong, they're using a version 1 UUID, which relies on a combination of timestamp and mac address for its uniqueness. However if you generate UUIDs fast enough, the timestamp won't have incremented yet. In this scenario, your UUID generation algorithm is supposed to track the last timestamp used and increment it by 1. They clearly failed to take that step.

However all version 1 UUIDs correctly generated by the same machine in a short period will exhibit obvious similarities, but ought to still be unique.

Show 4 more comments. Hoylen Hoylen 14k 5 5 gold badges 28 28 silver badges 16 16 bronze badges. Defaulting to a version 1 UUID has serious issues when they're generated by the same server for many people. The version 4 UUID is my default since you can quickly write something to generate one in any language or platform including javascript. Hoylen Well explained! Theoretically , it is uniquely assigned by the manufacturer.

One need not generate 10 million version 1 UUIDs in a second to encounter a duplicate; one must merely generate a batch of 16, UUIDs within the span of a single "tick" in order to overflow the sequence number. They are difficult to get right, so subject them to load tests before using them. Add a comment.

The answer to this may depend largely on the UUID version. Therefore, it's only as safe as the algorithms used to generate it. So pick a good library or generate it yourself and make sure you use a decent PRNG algorithm.

Quoting from Wikipedia : Thus, anyone can create a UUID and use it to identify something with reasonable confidence that the identifier will never be unintentionally used by anyone for anything else It goes on to explain in pretty good detail on how safe it actually is. Dave Vogt Dave Vogt But suppose hypothetically that they aren't. Stephen C Stephen C k 90 90 gold badges silver badges bronze badges. I just want to point out that the method number 2 basically defeats the main purpose of using UUID and you might as well just use a classic numbered ID at that point.

I disagree. The flaw in sequential numbered IDs is that they are too easy to guess. You should be able to implement method 2 in a way that makes the UUIDs difficult to guess. Well, yes and no. It depends on the context in which the ids are required to be unique. If they are only required to be unique in a closed system, then it is feasible to use short random strings and store them all in a database or something to check for duplicates.

But that doesn't give you guaranteed universal uniqueness. And if the number of unique ids generated over the lifetime of the system is large enough you will run into scaling problems, assuming that the unique ids are required to be unique over time Parappa Parappa 7, 2 2 gold badges 33 33 silver badges 38 38 bronze badges.

Been doing it for years. Never run into a problem. Posthuma Posthuma 1 1 silver badge 8 8 bronze badges. Here's a testing snippet for you to test it's uniquenes. Tschallacka Tschallacka Working so someone can tell me if I've messed up units: volume of grain of sand 0.

This is actually very helpful and has made me realize it's probably okay and there are other things to worry about. Obviously its a full box, otherwise I could have said "a box the size of the known universe which is 0. I think the packing factor is a much bigger issue with the above calc but at least it's conservative i.

Grant Wagner Grant Wagner Keep in mind that the reference linked here talks about Version 1 UUIDs which take information about the generating computer etc. Most other Answers talk about Version 4 which are totally random. The above linked Wikipedia article en. Toby Kelsey Toby Kelsey 73 5 5 bronze badges.

The Overflow Blog. In addition to this, it also introduces another random component just to be sure of its uniqueness. This means you are guaranteed to get a completely unique ID, unless you generate it from the same computer, and at the exact same time.

In that case, the chance of collision changes from impossible to very very small because of the random bits. This guaranteed uniqueness comes at the cost of anonymity. Because UUID v1 takes the time and your MAC address into consideration, this also means that someone could potentially identify the time and place i.

The generation of a v4 UUID is much simpler to comprehend. The bits that comprise a UUID v4 are generated randomly and with no inherent logic. Because of this, there is no way to identify information about the source by looking at the UUID. However, there is now a chance that a UUID could be duplicated.

The question is, do you need to worry about it? The short answer is no. If your application is mission critical for example, bank transactions or medical systems , you should still add a uniqueness constraint to avoid UUIDv4 collision.

An important point to note is UUID v5 is consistent. For example , if we have 68,,, UUIDs with 74 random bits , the probability of a duplicate would be 0. If a user was generating all UUIDs for a system using a single node, they may want to consider using UUID version 4 rather than 1, since the chance of collision is much greater.

About Duo. Careers Now Hiring! Product Product Explore Our Products Duo provides secure access to any application with a broad range of capabilities. Device Trust Ensure all devices meet security standards.

Adaptive Access Policies Block or grant access based on users' role, location, and more. Duo in Action Click through our instant demos to explore Duo features. Explore Demos. You need Duo. Start a Free Trial. Duo Free Free 10 users Simple identity verification with Duo Mobile for individuals or very small teams. Pricing Questions? Get in Touch Have questions about our plans? Solutions Explore Our Solutions Duo provides secure access for a variety of industries, projects, and companies. Customer Stories.

Passwordless Authentication Users can log into apps with biometrics, security keys or a mobile device instead of a password.

Already a Tech Partner? Duo Security Solution Providers Enhance existing security offerings, without adding complexity for clients. Support See All Support Have questions? Documentation Browse All Docs Get instructions and information on Duo installation, configuration, integration, maintenance, and much more. Resources See All Resources Explore research, strategy, and innovation in the information security industry.

InfoSec Glossary. Duo Labs Research We disrupt, derisk, and democratize complex security topics for the greatest possible impact.