how to prevent to customer to add same credit card - stripe-payments

Question

I am using stripe as my payment provider and storing encrypted credit card id in my db returned from stripe.
My question is that from GUI customer can add same card again. I see stripe do not prevent to add same card multiple time for same customer. Since stripe always generates different encrypted card id for same card so I can't use it to validate if same card is being added again.
How can stop customer to add same card again again.

Answer 1

Looks like I got that . I can use fingerprint returned in json response. I saw stripe dashboard and found that fingerprint is always same for same card which I was adding again again.
Here is json request and response to confirm
Request
{
"source": {
"number": "378282246310005",
"cvc": "123",
"address_line2": "4th Floor",
"address_line1": "140 2nd Street",
"address_country": "USA",
"name": "VIAY KUMAR",
"address_state": "CA",
"exp_month": 12,
"exp_year": 2015,
"address_zip": "94105",
"address_city": "San Francisco",
"object": "card"
}
}
Response
{
"id": "card_166H9rC8Y8JrMFgBh9GVsmNG",
"object": "card",
"status": null,
"exp_month": 12,
"exp_year": 2015,
"last4": "0005",
"country": "US",
"type": null,
"name": "VIAY KUMAR",
"customer": "cus_6IrxhfwXNyD1Uw",
"recipient": null,
"address_line1": "140 2nd Street",
"address_line2": "4th Floor",
"address_zip": "94105",
"address_city": "San Francisco",
"address_state": "CA",
"address_country": "USA",
"address_zip_check": "pass",
"address_line1_check": "pass",
"cvc_check": "pass",
"fingerprint": "TwjSA2KqPDhSMUvQ",
"brand": "American Express",
"funding": "credit"
}
added same card again and got different card id but same finger print :-)
Request
{
"source": {
"number": "378282246310005",
"cvc": "123",
"address_line2": "4th Floor",
"address_line1": "140 2nd Street",
"address_country": "USA",
"name": "VIAY KUMAR",
"address_state": "CA",
"exp_month": 12,
"exp_year": 2015,
"address_zip": "94105",
"address_city": "San Francisco",
"object": "card"
}
}
Response
{
"id": "card_166HKVC8Y8JrMFgBfvbHPgk2",
"object": "card",
"status": null,
"exp_month": 12,
"exp_year": 2015,
"last4": "0005",
"country": "US",
"type": null,
"name": "VIAY KUMAR",
"customer": "cus_6IrxhfwXNyD1Uw",
"recipient": null,
"address_line1": "140 2nd Street",
"address_line2": "4th Floor",
"address_zip": "94105",
"address_city": "San Francisco",
"address_state": "CA",
"address_country": "USA",
"address_zip_check": "pass",
"address_line1_check": "pass",
"cvc_check": "pass",
"fingerprint": "TwjSA2KqPDhSMUvQ",
"brand": "American Express",
"funding": "credit"
}

Answer 2

Thanks to Vijay for the above answer.
I've written the following Ruby code in my Rails app to check for this.
Replace the relevant #user.stripe_customer_id variable with your own.
# Retrieve the customer we're adding this token to
customer = Stripe::Customer.retrieve(#user.stripe_customer_id)
# Retrieve the token
token = Stripe::Token.retrieve(params[:stripeToken])
# The fingerprint of the card is stored in `card.fingerprint`
card_fingerprint = token.card.fingerprint
# Check if the card fingerprint submitted matches one of the customer's current sources
fingerprint_already_exists = customer.sources.any? {|source| source[:fingerprint] == card_fingerprint}
if fingerprint_already_exists
# You can do whatever you want here. I've personally set a flash message to let the user know this card is already on their account
flash[:warning] = "That card already exists on your account."
redirect_to user_path(#user) and return
end
# Continue adding the source as normal
customer.sources.create(source: params[:stripeToken])
# Anything else you want to do...
flash[:success] = "Your account has been updated."
redirect_to user_path(#user) and return

Answer 3

The fingerprint generated by Stripe is unique to each card. As taken from the docs:
fingerprint string
Uniquely identifies this particular card number. You can use this attribute to check whether two customers who’ve signed up with you are using the same card number, for example.
Assuming you already have a customer object at this point (either a new one or one to update), this will let you add a card and make it default, without duplicates:
// $customer = \Stripe\Customer::retrieve( $clicker->customer );
/**
* Add the card, but only if it does not exist. Make it default in any case.
**/
$token = \Stripe\Token::retrieve( $_POST['stripeToken'] );
$card = null;
/** Does this customer already have this card? If so, find it. **/
foreach ( $customer->sources['data'] as $source ) {
if ( $source['fingerprint'] == $token['card']->fingerprint ) {
$card = $source;
}
}
/** If not, add the new card to the customer **/
if ( is_null( $card ) ) {
$card = $customer->sources->create( array( 'source' => $_POST['stripeToken'] ) );
}
$customer->default_source = $card->id;
$customer->save();
You'd enclose this in the usual try/catch as exemplified by the docs.
That being said, from the point of view of the user, it will be better, if possible, to show them a list of their cards (last4 + expire date) and let them pick the one they'd like to charge – instead of asking for their info needlessly.