How to Quickly Mask a Credit Card Number

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So, often I have to show a masked credit card on the screen. However, I really want to go the extra mile and show the user a secure, fully masked credit card number that still reflects their original card. For example, if their credit card number is only 15 numbers long, I shouldn’t show a 16 character long string. So, I’ve developed this code snippet:

$masked = str_pad(substr($cc, -4), strlen($cc), '*', STR_PAD_LEFT);

This simply takes the credit card, substr() the last 4 digit into the str_pad() method as the input. Then, says the length of the output string should be strlen() of the actual input. The pad character is a *. Finally, pad everything on the left. This way, no matter what, the output length will be the same as the input string, and it will be padded correctly.

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