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re st: Encrypting and decrypting a field

From   "Jens Lauritsen" <>
To   <>
Subject   re st: Encrypting and decrypting a field
Date   Fri, 1 Apr 2005 12:14:39 +0200 (CEST)

> Has anyone on the list developed code for encrypting/decrypting a
> field  that they could send me?

Yes - we have.

One strategy would be:
Get epidata from (free ware). This includes possibilities
for a data entry system with encryption at field level. The algoritm is
AES-Rijndael - approved for high level encryption.

In addition to EpIData main program the functions for altering data
format, encryption, import and export are also available as the command
processor (batch) programme EpiC.

To do your proces in a reproducible manner from within Stata:
a. read the data into stata
b. save as stata file
c. call the epic program to  convert the data  to "rec" file data format
d. call the epic program to  convert the data  such that the id number
is encrypted
e. call the epic program to  convert the data  back to
Stata format
f. delete intermediate uncencrypted files

A drawback to this could be that EpIData and EpiC only runs on windows

As part of changing the whole EpiData project  to run on as well Linux
and Windows we have scheduled a plan to convert the source code to be
platform independent (and open-source).

In this "Sustainability" plan two parts are related to this:
1. The ability of the basic analysis programme to have functions
encrypt() and decrypt() with same algoritm as mentioned above

2. Uploading from local pc's to a central mysql database.
Some preliminary tests have been made on this. The tests show that we can:
a. upload a local data file (rec file format) to a central server (php
b. create or append to a MYSQL table  on the main server

The communication is secured by encryption with the AES-Rijndael
algoritm and no passwords are transmitted.  The full development of
this server/client application system will be part of the 
"Sustainability" plan which will be initiated once funding is secured (The
project has a total estimated budget of 250.000-350.000 Euro's  and will
start when 150.000 have been received - we have around 10.000 now).

The encrypt() - decrypt() are not scheduled now for the analysis programme
which is in beta test (v0.9 - build 21) from ,
but could be relatively soon.

The analysis programme will contain advanced datamanagement routines, but
simple analysis (basicly descriptive statistics, graphs and tables) and is
meant to be a "low end" equivalent, where people will use stata for
further analysis.

Jens Lauritsen
Coordinator and initiator of EpiData Project

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