Guid.Unix.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using Internal.Runtime.CompilerServices;

namespace System
{
    public partial struct Guid
    {
        // This will create a new random guid based on the https://www.ietf.org/rfc/rfc4122.txt
        public static unsafe Guid NewGuid()
        {
            Guid g;

            // Guid.NewGuid is often used as a cheap source of random data that are sometimes used for security purposes.
            // Windows implementation uses secure RNG to implement it. We use secure RNG for Unix too to avoid subtle security
            // vulnerabilities in applications that depend on it. See https://github.com/dotnet/runtime/issues/42752 for details.
            Interop.GetCryptographicallySecureRandomBytes((byte*)&g, sizeof(Guid));

            const ushort VersionMask = 0xF000;
            const ushort RandomGuidVersion = 0x4000;

            const byte ClockSeqHiAndReservedMask = 0xC0;
            const byte ClockSeqHiAndReservedValue = 0x80;

            // Modify bits indicating the type of the GUID

            unchecked
            {
                // time_hi_and_version
                Unsafe.AsRef(in g._c) = (short)((g._c & ~VersionMask) | RandomGuidVersion);
                // clock_seq_hi_and_reserved
                Unsafe.AsRef(in g._d) = (byte)((g._d & ~ClockSeqHiAndReservedMask) | ClockSeqHiAndReservedValue);
            }

            return g;
        }
    }
}