Guid.NewGuid Method
Definition
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Initializes a new instance of the Guid structure.
public:
static Guid NewGuid();public static Guid NewGuid ();static member NewGuid : unit -> GuidPublic Shared Function NewGuid () As GuidReturns
A new GUID object.
Examples
The following code example creates and displays the values of two Guid objects.
// Create and display the value of two GUIDs.
Guid g = Guid.NewGuid();
Console.WriteLine(g);
Console.WriteLine(Guid.NewGuid());
// This code example produces a result similar to the following:
// 0f8fad5b-d9cb-469f-a165-70867728950e
// 7c9e6679-7425-40de-944b-e07fc1f90ae7
open System
// Create and display the value of two GUIDs.
let g = Guid.NewGuid()
printfn $"{g}"
printfn $"{Guid.NewGuid()}"
// This code example produces a result similar to the following:
// 0f8fad5b-d9cb-469f-a165-70867728950e
// 7c9e6679-7425-40de-944b-e07fc1f90ae7
' This code example demonstrates the Guid.NewGuid() method.
Class Sample
Public Shared Sub Main()
Dim g As Guid
' Create and display the value of two GUIDs.
g = Guid.NewGuid()
Console.WriteLine(g)
Console.WriteLine(Guid.NewGuid())
End Sub
End Class
'
'This code example produces the following results:
'
'0f8fad5b-d9cb-469f-a165-70867728950e
'7c9e6679-7425-40de-944b-e07fc1f90ae7
'
Remarks
This is a convenient static method that you can call to get a new Guid. The method creates a Version 4 Universally Unique Identifier (UUID) as described in RFC 4122, Sec. 4.4. The returned Guid is guaranteed to not equal Guid.Empty.
On Windows, this function wraps a call to the CoCreateGuid function. The generated GUID contains 122 bits of strong entropy.
On non-Windows platforms, starting with .NET 6, this function calls the OS's underlying cryptographically secure pseudo-random number generator (CSPRNG) to generate 122 bits of strong entropy. In previous versions of .NET, the entropy is not guaranteed to be generated by a CSPRNG.
It is recommended that applications not use the NewGuid method for cryptographic purposes. First, since a Version 4 UUID has a partially predictable bit pattern, the NewGuid function cannot serve as a proper cryptographic pseudo-random function (PRF). If the output of NewGuid is given to a cryptographic component which requires its input to be generated by a proper PRF, the cryptographic component may not be able to maintain its security properties. Second, NewGuid utilizes at most 122 bits of entropy, regardless of platform. Some cryptographic components set a minimum entropy level on their inputs as a matter of policy. Such policies often set the minimum entropy level at 128 bits or higher. Passing the output of NewGuid to such a routine may violate its policy.
If an application requires random data for cryptographic purposes, consider using a static method on the RandomNumberGenerator class. That class provides a random number generator suitable for cryptographic use.
