Guids

Helper types for creating and interpreting GUIDs.

Creating GUIDs

The following GUID types are supported:

• Version 5 GUIDs ("Named SHA-1 GUIDs"), generated from a Namespace GUID and a Name, which are hashed together with SHA-1. See GuidFactory.CreateSha1.
• Version 4 GUIDs ("Random GUIDs"), generated randomly. See GuidFactory.CreateRandom.
• Version 3 GUIDs ("Named MD5 GUIDs"), generated from a Namespace GUID and a Name, which are hashed together with MD5. See GuidFactory.CreateMd5.

The version 3 and 5 algorithms have been verified against independent implementations, most notably the Python uuid module, and are fully compatible with its GUIDs.

Decoding GUIDs

Any Guid can be decoded into a DecodedGuid, which has a variety of properties for extracting information. E.g., you can extract the timestamp and MAC address of the GUID found in the Melissa virus as such:

var guid = Guid.Parse("572858EA-36DD-11D2-885F-004033E0078E");
var decoded = guid.Decode();
Assert.Equal(GuidVariant.Rfc4122, decoded.Variant);
Assert.Equal(GuidVersion.TimeBased, decoded.Version);
Assert.Equal(new DateTime(1998, 8, 18, 20, 52, 22, 510, DateTimeKind.Utc).AddTicks(10), decoded.CreateTime);
Assert.Equal(new byte[] { 0x00, 0x40, 0x33, 0xE0, 0x07, 0x8E }, decoded.Node);
Assert.True(decoded.NodeIsMac);

Endianness

This library also has a few helper methods for working with big-endian GUID byte arrays, something not supported by the native Guid type. Note that the string representation of a Guid is always big-endian, but the .NET Guid uses little-endian byte array representations.

Guids can be created from either big- or little-endian byte arrays. See GuidFactory.FromLittleEndianByteArray and GuidFactory.FromBigEndianByteArray.

Similarly, Guids can be converted to a big-endian byte array. See the ToBigEndianByteArray extension method. The built-in Guid.ToByteArray converts to a little-endian byte array.