SHIKHAR GHOSH, Open Market's 38-year-old chairman and co-founder, allows dogs in his company's Cambridge (Mass.) offices, but that's his only quirk. Open Market builds secure software for critical commercial applications on the Internet. It has helped set up the hottest commercial Web sites, including those of Banc One and Ziff-Davis, which rely on Open Market's software for handling credit-card transactions and filling orders. Ghosh may be the one holding the keys to really doing business on the Net.