Methods and apparatus for conducting offline commerce transactions that use a barcode as an alternative means for personal identification. The user represented in the bar code format, User ID Barcode, is generated from a number that uniquely identifies the user. Numbers such as a cell phone number or a credit card number may be used to generate the User ID Barcode. These numbers are prefixed with a special character before they are converted to the barcode format. Prefixing a special character is necessary so that the bar code generated can be distinguished from any bar code representing products being sold. If a credit card number is used, the User ID Barcode is printed on the back of the credit card which then becomes a 2 and 1 credit card.