Lawyers for Texas Instruments are taking aim at a group of calculator enthusiasts who posted the cryptographic keys used to modify the devices so they run custom-designed software. Over the past few weeks, TI has sent webmasters letters invoking the DMCA, or US Digital Millennium Copyright Act (PDF), and demanding they remove the keys published in blog postings. The private keys are needed to sign operating systems before they work on a wide variety of calculator models designed by the Dallas-based electronics manufacturer.