If I create two GUIDs then I understand they will be unique but is part of that dependent on the time. I would like to create a random string that is completely random.
Maybe if someone knows how a GUID is created that would help me to understand.
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- en.wikipedia.org/wiki/Globally_unique_identifier#AlgorithmFrédéric Hamidi– Frédéric Hamidi2014-06-26 07:42:58 +00:00Commented Jun 26, 2014 at 7:42
- There is a somewhat related question here: stackoverflow.com/questions/1752004/…David Brabant– David Brabant2014-06-26 07:43:51 +00:00Commented Jun 26, 2014 at 7:43
- the c# implementation calls CoCreateGuid, which calls UuidCreate msdn.microsoft.com/en-US/library/windows/desktop/aa379205.aspx "The UuidCreate function generates a UUID that cannot be traced to the ethernet address of the computer on which it was generated. It also cannot be associated with other UUIDs created on the same computer. "Jay– Jay2014-06-26 07:48:49 +00:00Commented Jun 26, 2014 at 7:48
- 2Unless you have access to specialized hardware, there is no way for a computer to create a random value that is truly random. It will always follow some kind of pattern. Also, no, you should not rely on any part of the guid as a timestamp. If you need a timestamp, implement a timestamp. A guid is a different type of value, meant for uniqueness.Lasse V. Karlsen– Lasse V. Karlsen2014-06-26 07:49:09 +00:00Commented Jun 26, 2014 at 7:49
- possible duplicate of Is a GUID unique 100% of the time?Tolga Evcimen– Tolga Evcimen2014-06-26 07:49:31 +00:00Commented Jun 26, 2014 at 7:49
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2 Answers
If I create GUIDs then is there a way I can check if one GUID is created after another?
No. There are lots of ways to make GUIDs. Nothing in the GUID encodes the time. It is possible that a poorly implemented GUID generator would encode the time of generation, but in general, given a GUID, you do not know the algorithm used to generate it.
I would like to create a random string that is completely random.
Use a good quality random number generator. Although be warned that its hard to find true random number generators on a general computer. Usually the best you can do is use a pseudo random number generator.
answered Jun 26, 2014 at 7:49
David Heffernan
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3 Comments
David Heffernan
@RussellHorwood Simply don't exist. Depends on your definitions I suppose. I'm thinking of the sort of RNGs described here: en.wikipedia.org/wiki/…
David Heffernan
@RussellHorwood A deterministic computation yields a PRNG. But true RNGs do exist. They just aren't quite as practical on a general purpose computer. That's all I meant. I suppose I was trying to point out to the asker that a desire for "completely random" will not be met perfectly by a PRNG.
Russell Horwood
None of this is important.
-- Wikipedia's answers this clearly --
GUIDs are usually stored as 128-bit values, and are commonly displayed as 32 hexadecimal digits with groups separated by hyphens, such as {21EC2020-3AEA-4069-A2DD-08002B30309D}. GUIDs generated from random numbers sometimes contain 6 fixed bits saying they are random and 122 random bits; the total number of unique such GUIDs is 2122 (approximately 5.3×1036). This number is so large that the probability of the same number being generated randomly twice is negligible; however other GUID versions have different uniqueness properties and probabilities, ranging from guaranteed uniqueness to likely non-uniqueness. Assuming uniform probability for simplicity, the probability of one duplicate would be about 50% if every person on earth as of 2014 owned 600 million GUIDs.
Here is the source for C# if you want a more intrinsic understanding: http://referencesource.microsoft.com/#mscorlib/system/guid.cs
