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I saw that I can create name-based UUID / deterministic GUID, see https://stackoverflow.com/a/5657517/7556646.

Example of a non-name-based UUID:

System.Guid id1 = System.Guid.NewGuid() // id1 = {780dc51b-8eb3-4d66-b76d-8ab44e1311e6} for example

Example of a named-based UUID:

string filePath = "Test"; System.Guid id2 = GuidUtility.Create(GuidUtility.UrlNamespace, filePath); // id2 = {64ad81d8-15e2-5110-9024-83c64dc485f9}

Now I've the following question: Is there a way for example in C# to find out if GUID is a name-based UUID or a non-named-based UUID?

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    it would help if you pasted the output of each uuid type below the corresponding code Commented Feb 7, 2018 at 16:24
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    Not a complete answer, but if someone else wants to include it in theirs, this section of GuidUtility.Create() appears to leave a signature that you can check for in name-based UUIDs. Commented Feb 7, 2018 at 16:31

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In general for non-named-based guid the 13th digit (right after the second dash) will be a 4 and for named based it will be a 3 or 5.

This isn't universally true but will be for the code you are using.

"0b5415ec-657c-4a80-9199-f7993aff3908"

"275b74ef-e22a-59d6-8b2c-4face1410f59"

The version number is decribed in RFC 4122:

 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | time_low | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | time_mid | time_hi_and_version | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |clk_seq_hi_res | clk_seq_low | node (0-1) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | node (2-5) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The version number is in the most significant 4 bits of the time stamp (bits 4 through 7 of the time_hi_and_version field). The following table lists the currently-defined versions for this UUID variant:

  1. The time-based version specified in this document.
  2. DCE Security version, with embedded POSIX UIDs.
  3. The name-based version specified in this document that uses MD5 hashing.
  4. The randomly or pseudo-randomly generated version specified in this document.
  5. The name-based version specified in this document that uses SHA-1 hashing.

With the following code you could check if a GUID is name-based:

public static bool IsNameBased(Guid id) { byte version = GetVersion(id); return version == 3 || version == 5; } public static byte GetVersion(Guid id) { byte[] byte_array = id.ToByteArray(); byte version = (byte)(byte_array[7] >> 4); return version; }
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3 Comments

Going off of memory, I believe you are correct, but for credibility it would benefit you to cite a well-known source to support your claim. Consider editing your answer to include a link to a source that explains this convention, and use a > quoteblock to include relevant information from the link.
Version bits are described in RFC 4122
Wow, I always thought GUIDs are completely random. I never realized (I checked, you were right) that one digit is constant.

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