XOR data encryption

I am trying to store some credit card numbers in a database, along with the rest of the data (dangerous, I know). Unforunately, I am using a provider that doesn't have the mcrypt functions compiled into PHP, so I guess I am stuck using the swiss-cheese like XOR method of encryption. My client is too cheap to put a separate server to store the credit card numbers, so I am stuck using symmetrical encryption. NEvertheless, I want to implement XOR, but I can't find an example on the net that shows how to do it in PHP. I know the philosophy behind it, but hwo do you do it? Do you convert the letters in the passphrase and the credit card number into 0 1 binary and then XOR that? What commands are there iN PHP that converts from alphanumeric to binary? If someone could post an example, that would be great. - Steve