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Re: RE: st: RE: RE: Encryption of data


From   [email protected] (William Gould, StataCorp LP)
To   [email protected]
Subject   Re: RE: st: RE: RE: Encryption of data
Date   Thu, 14 Jun 2007 09:27:39 -0500

Continuing the discussion on anonomization of ids, I wrote,

> There is no additional security to be gained by doing that.  
> Ties do not
> matter in this case.

and Hendri Adriaens <[email protected]> just replied, 

> It might not matter for security, but for my application it does. The
> information from the master data set (that will be anonymised) will have to
> be merged into a new dataset (to be anonymised with the mapping). If the
> mapping contains ties, -merge- wouldn't know which of the tied records to
> insert in the new dataset.

No.

There is no problem.  The mapping will not contain ties even if ties 
arise due to the random numbers drawn.  Every person will in the data 
will have a unique id.  Nick Cox's point was that, if we reran the 
program that generated the mapping, it is possible that it would create 
a different mapping, and my point is response was, that doesn't matter.
In either case, the mapping will be unique.  All that might happen is 
is that 

                     uid    newid
             123-45-6789      100
             999-99-9999      101

the first time we ran, and 

                     uid    newid
             999-99-9999      100
             123-45-6789      101

the second.  It doesn't matter what the mapping is, however, because once 
we set it, we will continue to use that mapping, and one is as good as 
the other, cyptographically speaking.

-- Bill
[email protected]
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