What is the relationship between CID (security number) and credit card
number on credit cards.

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Request for Question Clarification by efn-ga on 22 Jun 2004 22:04 PDT

Hi hlman,

The credit card number is an input to the calculation of the CID.  I
can't tell you exactly how the calculation works, but I can point you
to a page that identifies the inputs and has some discussion of how
they are used.  Would that be a satisfactory answer to your question?

--efn

None. They are independent of each other which is why they contribute to security.

The CID does only exist on american express cards. Mastercard and Visa
use CVC / CVV -Numbers to verify that the used card is the authentic
one. I don't know how the CID at amex works, but the cvc/cvv number
for mastercard/visa is used for the following:
The CVC / CVV Number is only known by the credit card institution and
the cardholder. In case of skimming (copied card informations from the
magnetic stripe and recorded on a new / different plastic) the
cardholder usually does not remark his card is beeing copied, and the
skimmer cannot note this small printed numbers and cannot either print
them on a new card, for they are not embossed, but directly printed on
the card plastic. The CVC/CVV number is registered at the data bank of
the credit card institution. nobody else can know it but the
institution and the owner of the card.
In case of fraud, the credit card institution can quickly figure out
wether the card at the point of sale is the authentic one or not and,
if necessary, alarm the police.
I'm sorry for my bad english, I hope you understand what I mean.
Regards

p.s. if you want to know what to do to avoid credit card fraud, i'll
be glad to provide you more detailed information, for I once worked
for a credit card institution and saw hundreds of cases of fraud.

Wow, Girl from Mars

Your English is fine!

What part of Mars do you come from?

(I'm thinking of taking a flight there soon.)