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From: David Empson on 17 Jun 2010 03:00 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. > > It wouldn't be hard for a crook to generate a random credit card number > > with a valid checksum, and the first four digits known to be valid (they > > identify the card issuer and the credit card type). > > the first digit is the credit card type (5=mastercard, 4=visa) and the > first six digits identify the bank. 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. It doesn't go as far as identifying the bank. -- David Empson dempson(a)actrix.gen.nz
From: nospam on 17 Jun 2010 07:08 In article <1jk8mgp.52bbmo1d2hhuzN%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. it needs to access each digit, and converting from text in filemaker would probably be a pain. once it's done with that, the rest is trivial. > > the first digit is the credit card type (5=mastercard, 4=visa) and the > > first six digits identify the bank. > > 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. > > It doesn't go as far as identifying the bank. yes it does. <http://en.wikipedia.org/wiki/Bank_card_number> The first 6 digits of the credit card number are known as the Issuer Identification Number (IIN). These identify the institution that issued the card to the card holder. The rest of the number is allocated by the issuer.
From: nospam on 17 Jun 2010 07:14 In article <michelle-FF7ED1.21474116062010(a)62-183-169-81.bb.dnainternet.fi>, Michelle Steiner <michelle(a)michelle.org> wrote: > > it's true, but there is an additional 3 digit cvv code on the back of > > the card so even if you can hack the number on the front, you still have > > some additional work to do. > > 4 digits on the front for AMEX. Plus many machines (including gas pumps > and at the Apple Stores) require your ZIP code for AMEX cards. i've seen amex cards with a 3 digit code on the back in addition to the 4 digit code on the front, and gas pumps ask for zip code for all credit card transactions, not just amex.
From: David Empson on 17 Jun 2010 08:17 nospam <nospam(a)nospam.invalid> wrote: > In article <1jk8mgp.52bbmo1d2hhuzN%dempson(a)actrix.gen.nz>, David Empson > <dempson(a)actrix.gen.nz> wrote: > > > > the first digit is the credit card type (5=mastercard, 4=visa) and the > > > first six digits identify the bank. > > > > 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. > > > > It doesn't go as far as identifying the bank. > > yes it does. I was talking about what this database (Card Validator) was doing, not what the number actually means. The database has a list of card types and how they map to the initial digits (possibly incomplete), but it doesn't have a list of card issuers. > <http://en.wikipedia.org/wiki/Bank_card_number> > > The first 6 digits of the credit card number are known as the Issuer > Identification Number (IIN). These identify the institution that > issued the card to the card holder. The rest of the number is > allocated by the issuer. -- David Empson dempson(a)actrix.gen.nz
From: Wes Groleau on 17 Jun 2010 08:55
On 06-17-2010 08:50, Michelle Steiner 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. -- Wes Groleau A parent's encounter with his daughter taking Latin http://Ideas.Lang-Learn.us/barrett?itemid=1434 |