Date:         Thu, 21 Feb 2002 10:42:39 -0800
Reply-To:     Cassell.David@EPAMAIL.EPA.GOV
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         "David L. Cassell" <Cassell.David@EPAMAIL.EPA.GOV>
Subject:      Re: Encrypting a field in the SAS file!
Content-type: text/plain; charset=us-ascii

Stig Eide <stigeide@YAHOO.COM> wrote:
> I don't understand how you can use BXOR() to encrypt a string?
> Bxor needs two numerical arguments?
>Could you please provide me with an example?

and Rashida Patwa wrote in private e-mail [in part]:
> Do you have an example of such array??

Well, I guess I was spectacularly unclear in my previous message.
So let me give a trivial example of what I had in mind.  Microsoft
has used XOR as a weak cryptographic tool [just look up your screen
saver password's transformed version on your system, and you'll see
it is your actual password XOR'ed to hide it from only the most naive
observers], and that's what I was thinking of.  Stig is right [of
course], but that's what rank() and byte() are for.  So look at this
code:

data temp1;
  input string1 $char12.;
  datalines;
123456789012
XXX-XX-XXXX
X23J47HIKE!!
;
run;

data temp2;
  length newstring $ 12;
  drop _i_;
  array secret {12} $ _temporary_ ('B','i','l','l','G','a','t','e','s',
'I','s','A');
                                /* Complete this sentence yourself! */
  array alter {12} $ _temporary_;
  set temp1;
  do _i_=1 to 12;  /* Paul would have used _iorc_ here :-) */
    alter{_i_} = substr(string1,_i_,1);
     alter{_i_} = byte( bxor( rank(alter{_i_}), rank(secret{_i_}) ) );
     /* put alter{_i_}=hex.; */
      /* uncomment this to see how the data are actually stored and
transformed */
     substr(newstring,_i_,1) = alter{_i_};
    end;
  run;

proc print data=temp2; run;


Perhaps this explains a little better.  It is clearly not perfect.  I
chose
some XORs which yield non-printing characters.  But this is really not
the
way to do encryption anyway, so I'm not that concerned about its
utility.

David
--
David Cassell, CSC
Cassell.David@epa.gov
Senior computing specialist
mathematical statistician