Guid.NewGuid Method

Definition

Namespace:

System

Assembly:

System.Runtime.dll

Source:

Guid.Unix.cs

Initializes a new instance of the Guid structure.

public:
 static Guid NewGuid();

public static Guid NewGuid ();

static member NewGuid : unit -> Guid

Public Shared Function NewGuid () As Guid

Returns

Guid

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.