[ZiiP]carrot;14015087 said:
Its storing the values as ints...in a txt file
eeps
At a minimum, PCI DSS requires PAN (Primary Account Number: card number) to be rendered unreadable anywhere it is stored – including portable digital media, backup media, and in logs. Software solutions for this requirement may include one of the following:
• One-way hash functions based on strong cryptography – also called hashed index, which displays only index data that point to records in the database where sensitive data actually reside.
• Truncation – removing a data segment, such as showing only the last four digits.
• Index tokens and securely stored pads – encryption algorithm that combines sensitive plain text data with a random key or “pad” that works only once.
• Strong cryptography – with associated key management processes and procedures. Refer to the PCI DSS and PA-DSS Glossary of Terms, Abbreviations and Acronyms for the definition of “strong cryptography.”
Some cryptography solutions encrypt specific fields of information stored in a database; others encrypt a singular file or even the entire disk where data is stored. If full-disk encryption is used, logical access must be managed independently of native operating system access control mechanisms. Decryption keys must not be tied to user accounts. Encryption keys used for encryption of cardholder data must be protected against both disclosure and misuse. All key management processes and procedures for keys used for encryption of cardholder data must be fully documented and implemented.
Edit: and if your still bored after writing a secure encrypt & key management system you could always lookup the bin number and id the "card"
http://en.wikipedia.org/wiki/List_of_Bank_Identification_Numbers 
