uuid types 3 and 5

[Martin Baxter]

On 09/01/14 19:05, Mark Wieder wrote:
> Martin Baxter <mblivecode at ...> writes:
> 
>>
>> Was looking at the uuid command.
>>
>> Type 4 is straightforward enough.
>>
>> Types 3 and 5 have me baffled though. Does anyone know what those types
>> are used for? I can't even guess, nor have my web searches led me to any
>> information about their usage.
> 
> Here's my take on uuid types 3 and 5:
> 
> 1. Don't bother with type 3 - it's been deprecated in favor of type 5. See
> RFC 4122 for more details.
> 2. Both these types are for generating uuids that are limited to a specific
> namespace in scope, and thus you can feed the namespace as an argument and
> guarantee that uuids generated at the same time *within the same namespace*
> will be identical.
> 

Why would I want identical uuids though? Aren't they supposed to be unique?

I have read that type 3 is deprecated, on the basis that md5 is not
considered secure these days, although I think that was one thing that
confused me because uuid is nothing to do with encryption or obfuscation
as far as I was aware.

Is it perhaps that the "namespace" has to be obfuscated so that
"unspecified unauthorised persons" don't also deliberately create uuids
based on the same namespace?

If that is the case, you wouldn't want to use this in an open-source
context, because the namespace would be a secret?

Or am I not getting it?

Martin