The Public Key idea is excellent, and is part of the solution. Unfortunately, I cannot use a public key as part of the data entry toolset - because I am restrained by using MS Access for data entry. If I was able to do the data entry system in Perl, your suggestion (and the module that would likely get most of the heavy lifting done) would be a godsend.
I fear I have asked a question without a complete enough spec, and so have become mired in clarifications, rather than looking at solutions. I should learn my lesson, but apparently, I have not yet done so.