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From: Thomas R. Kettler on 17 Jun 2010 09:52
In article <1jk8mgp.52bbmo1d2hhuzN%dempson(a)actrix.gen.nz>,
dempson(a)actrix.gen.nz (David Empson) wrote:

> nospam <nospam(a)nospam.invalid> wrote:
>
> > In article <1jk8aq9.nyxhig1rnt12tN%dempson(a)actrix.gen.nz>, David Empson
> > <dempson(a)actrix.gen.nz> wrote:
> >
> > > I have a FileMaker Pro database which includes the formula for verifying
> > > that a credit card number is valid. It isn't particularly long but it is
> > > complex enough that I haven't tried to analyse it.
> >
> > it's actually very simple.
>
> I expect so. I meant that it is complex due to being a FileMaker
> forumula which is doing a lot of text processing, conversion to numbers,
> calculations, nested IF statements, etc., which makes it hard to read.

Nearly all credit cards use the Luhn algorithm which is the following:

<http://en.wikipedia.org/wiki/Luhn_algorithm>

I believe the validation codes have to follow it also, but separately
from the credit card number.
--
Remove blown from email address to reply.
From: nospam on 17 Jun 2010 10:04
In article
<michelle-DA038E.05505017062010(a)62-183-169-81.bb.dnainternet.fi>,
Michelle Steiner <michelle(a)michelle.org> wrote:

> And I've never had a gas pump ask for my ZIP code when I've used a VISA or
> Mastercard.

i have.
From: nospam on 17 Jun 2010 10:04
In article
<michelle-18321B.05485717062010(a)62-183-169-81.bb.dnainternet.fi>,
Michelle Steiner <michelle(a)michelle.org> wrote:

> I'm missing something here. Where in the article does it say that the
> FileMaker database checks those six digits?

from what he said, filemaker was checking the validity of the entire
credit card number, not the bank id.
From: nospam on 17 Jun 2010 10:04
In article
<michelle-138BE2.05372917062010(a)62-183-169-81.bb.dnainternet.fi>,
Michelle Steiner <michelle(a)michelle.org> wrote:

> > This database is checking for many different combinations of the first
> > four digits. It identifies anything starting with 4 as Visa, 5 with
> > certain values of the second digit as Mastercard, and a whole bunch of
> > other card types which I haven't looked into in detail.
>
> American Express cards all begin with 3.

others also begin with 3.
From: =?ISO-8859-1?Q?Kir=E1ly?= on 17 Jun 2010 12:57
In comp.sys.mac.apps Wes Groleau <Groleau+news(a)freeshell.org> wrote:
> > And I've never had a gas pump ask for my ZIP code when I've used a VISA or
> > Mastercard.
>
> My experience is that around ten percent do.

I wonder what would happen if I visited the USA and used my credit card at
such a gas pump. I usually use cash outside of Canada so I will
probably never find out.

--
K.

Lang may your lum reek.
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