need insights on encrypting and uploading ASCII file using PHP

We have various labs that submit coliform sample results in an ASCII file, quoted/comma delimited. We are being asked to encrypt this file for internet transfer. We are also being asked to create a secure process by which to transfer this file across the interent. Currently: the lab pushes and button and generates the ASCII file (12 columns) the lab logs in to a PHP webpage and uses the file upload input to submit the file. If data is valid, file is saved on our server in a folder where we can pull it into the respective tables. Be nice to have some insights on how to encrypt this file at the source and how to transfer the file securely. We keep hearing the words, "digital signature". Thanks in advance, John A. Davis Programmer State of Oregon DHS OIS CNE, MCSE "Don't think of the problem, think of the solution"