how to limit the length of GUID in c# to send password

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how to limit the length of GUID in c# to send password

Posted 28-May-12 2:48am

Aparnashreenivas

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DaveAuld 28-May-12 8:50am

You are not making a lot of sense with that question. A GUID is a specific type, http://msdn.microsoft.com/en-us/library/system.guid.newguid.aspx, so you cannot limit its length. You would need to come up with your own identifier scheme. Just use a simple int.

Keith Barrow 28-May-12 8:56am

Guids are Fixed length. They are this long to make it massively unlikely that two will be the same, reducing the length reduces their effectiveness.
Can you explain what it is you are trying to acheive (rather than what it is you are doing), sending a guid to the user is probably wrong especially if (I assume) you want to make it shorter and easier for them to read.

Sinisa Hajnal 4-Feb-16 4:02am

Guids are internally just 16 bytes of random data- you could convert them to base64 strings and cut last two characters (which are == anyhow)

3 solutions

Solution 1

If you are using the Guid to generate a random password, then use the Substring() function to get a part of it.

C#

string strPassword = Guid.NewGuid().ToString("N").Substring(0, 12);

However , keep in mind that a Guid is unique and the part of it may not be unique.

http://msdn.microsoft.com/en-us/library/s6tk2z69[^]

Posted 28-May-12 3:39am

bbirajdar

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DaveAuld 28-May-12 10:09am

They are not guaranteed to be unique, even the link you provided links through to the GUID page which states, 'A GUID is a 128-bit integer (16 bytes) that can be used across all computers and networks wherever a unique identifier is required. Such an identifier has a very low probability of being duplicated.'
As you can see, it states, very low probability!

Keith Barrow 28-May-12 10:33am

I wish I could 5 this comment!

bbirajdar 29-May-12 2:38am

I think we should talk in terms of numbers. Your comment is 1/2^128 % correct .

Guids are designed be unique and not random. Using a decent computer which generates a Guid in every 100 nanoseconds, 2^128 guids can be generated and it takes about 1.6 billion years before it runs out of Guids. So the probability of generating the same Guid twice is 1/2^128. And yes, it guaranteed that the same Guid is not generated on the same computer in 1.6 billion years (unless you turn back your system clock ).

The most important thing is that , guid should not be used to generate passwords, since they can be predicted.

bbirajdar 29-May-12 4:14am

http://stackoverflow.com/questions/1705008/simple-proof-that-guid-is-not-unique

Solution 3

string strPassword = Guid.NewGuid().ToString().Substring(0, Guid.NewGuid().ToString().IndexOf("-"));

This will generate an unique alpha numeric password.

For example if the generated GUID is "0f8fad5b-d9cb-469f-a165-70867728950e" then it will retrieve only "0f8fad5b". It will be useful for password generation.

Try this..

Posted 29-Dec-14 4:32am

Senthilaan

Updated 29-Dec-14 4:36am

v2

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Member 14735464 21-Feb-22 5:20am

not unique

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DaveAuld · Accepted Answer · 2012-05-28T04:22:00

Solution 2

If you are looking to generate random passwords why not use the following method which is part of the .Net Framework (from V2 onwards)

System.Web.Security.Membership.GeneratePassword

See here;
http://msdn.microsoft.com/en-us/library/ms152017[^]

Posted 28-May-12 4:22am

DaveAuld