Tuesday, October 05, 2010

Computing per-service SIDs without sc.exe

How it's done is well known:

When configured to have a per-service SID (i.e. type of SID either "Unrestricted" or "Restricted"), the service SID is computed as S-1-5-80-{SHA-1(service name in uppercase)}

Here's a quick script to do it, that can be the basis for including the computation programmatically into e.g. installer generation.

So running it we get:

>& 'C:\Program Files\FSharp-2.0.0.0\bin\fsi.exe' .\ssid.fsx MyService
S-1-5-80-517257762-1253276234-605902578-3995580692-1133959824
>

which compares nicely with:

>sc showsid MyService

NAME: MyService
SERVICE SID: S-1-5-80-517257762-1253276234-605902578-3995580692-1133959824
>

where each of the 5 trailing facets is just the decimal representation of 4 bytes of the SHA-1 hash taken as a little-endian unsigned integer.

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