Implementation of a secure office system based on cryptography

This article describes the implementation of a secure office system based on cryptography. The implementation uses a hybrid scheme of conventional DES cryptography and RSA public key cryptography. Randomly generated DES keys encrypt messages and files, and the DES keys themselves and the one-way hash of messages are encrypted and signed with RSA keys. The system provides secure e-mail (including registered e-mail and electronic notary), secure two-way channels and protected user files. Timestamps and a special signed public key file help reduce the need for an online central authority involved in all transactions.