Credit Card Validation

How credit cards are checked for their validity.What is the method adopted to verify that the credit card is valid.Is there any algorithm used?If so please explain and give an example
LVL 10
rajesh_balaAsked:
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xabiConnect With a Mentor Commented:
Here goes the code:

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<html>
<head>
<title>order form</title></head>
<script language="JavaScript">
<!--
function isCreditCard(st) {
 if (st.length > 19) return (false)
 sum = 0; mul = 1; l = st.length
 for (i = 0; i < l; i++) {
  digit = st.substring(l-i-1,l-i)
  tproduct = parseInt(digit ,10)*mul
  if (tproduct >= 10) sum += (tproduct % 10) + 1
  else sum += tproduct
  if (mul == 1) mul++
  else mul--
 }
 if ((sum % 10) == 0) return (true)
 else return (false)
}

function isVisa(cc) {
 if (((cc.length == 16) || (cc.length == 13)) && (cc.substring(0,1) == 4)) return isCreditCard(cc)
 return false
}

function isMasterCard(cc) {
 firstdig = cc.substring(0,1)
 seconddig = cc.substring(1,2)
 if ((cc.length == 16) && (firstdig == 5) && ((seconddig >= 1) && (seconddig <= 5))) return isCreditCard(cc)
 return false
}

function isAmericanExpress(cc) {
 firstdig = cc.substring(0,1)
 seconddig = cc.substring(1,2)
 if ((cc.length == 15) && (firstdig == 3) && ((seconddig == 4) || (seconddig == 7))) return isCreditCard(cc)
 return false
}

function isDinersClub(cc) {
 firstdig = cc.substring(0,1)
 seconddig = cc.substring(1,2)
 if ((cc.length == 14) && (firstdig == 3) && ((seconddig == 0) || (seconddig == 6) || (seconddig == 8))) return isCreditCard(cc)
 return false
}

function isCarteBlanche(cc) {
 return isDinersClub(cc)
}

function isDiscover(cc) {
 first4digs = cc.substring(0,4)
 if ((cc.length == 16) && (first4digs == "6011")) return isCreditCard(cc)
 return false
}

function isEnRoute(cc) {
 first4digs = cc.substring(0,4)
 if ((cc.length == 15) && ((first4digs == "2014") || (first4digs == "2149"))) return isCreditCard(cc)
 return false
}

function isJCB(cc) {
 first4digs = cc.substring(0,4)
 if ((cc.length == 16) && ((first4digs == "3088") || (first4digs == "3096") || (first4digs == "3112") || (first4digs == "3158") || (first4digs == "3337") || (first4digs == "3528"))) return isCreditCard(cc)
 return false
}

function check_values() {
 iCardType   = document.myform.CreditCard_Type.selectedIndex
 iCardNumber = document.myform.CreditCard_Number.value
 bResult = false
 if (iCardType == 0) bResult = isVisa(iCardNumber)
 if (iCardType == 1) bResult = isMasterCard(iCardNumber)
 if (iCardType == 2) bResult = isAmericanExpress(iCardNumber)
 if (iCardType == 3) bResult = isDinersClub(iCardNumber)
 if (iCardType == 4) bResult = isCarteBlanche(iCardNumber)
 if (iCardType == 5) bResult = isDiscover(iCardNumber)
 if (iCardType == 6) bResult = isEnRoute(iCardNumber)
 if (iCardType == 7) bResult = isJCB(iCardNumber)
 if (bResult == false) alert("Invalid Credit Card Number")
 return bResult
}
//-->
</script>
</head>
<body>
<form name="myform" onSubmit="return(check_values())">
<table>
  <tr>
    <td>Credit Card Type</td>
    <td>
     <select name="CreditCard_Type">
      <option>Visa</option>
      <option>MasterCard</option>
      <option>AmericanExpress</option>
      <option>DinersClub</option>
      <option>CarteBlanche</option>
      <option>Discover</option>
      <option>EnRoute</option>
      <option>JCB</option>
     </select>
    </td>
  </tr>
  <tr>
    <td>Credit Card Number</td>
    <td><input type="text" size="38" maxlength="19" name="CreditCard_Number"></td>
  </tr>
</table>
<input type="submit" value=" Submit Request">
<input type="reset" value=" Clear "> 
</form>
<br>
</body>
</html>
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xabi
0
 
cojonesCommented:
No argorithm, its sent out across a connection to verify by the banks.  
0
 
ozoCommented:
Do you just want to verify the checksum, or do you need to know whether the card is over its credit limit?
0
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xabiCommented:
Here you will find the code in javascript:

http://developer.netscape.com/tech/javascript/index.html

In the script CheckForm.js you will find a function to check the creditcard number.

xabi
0
 
ytgprasadCommented:
there is a alogorithm called LUHN algorithm for basic validation of the CARD numbers of certain Banks
0
 
ytgprasadCommented:
for the LUHN algorithm and this site http://www.cybercash.com/cybercash/merchants/support/luhn.html may be useful, check out
0
 
xabiCommented:
xabi changed the proposed answer to a comment
0
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