Abstract: An encryption/decryption system for providing restricted use of each key in a plurality of keys to preserve confidentiality of the plurality of keys. Each key is usable by an associated user in a public key infrastructure to encrypt and decrypt data. The encryption/decryption system comprises a key storage means for storing a plurality of keys, user authentication means for determining whether a prospective user of a key in the plurality of keys is the associated user of the key, and an encryption/decryption means for encrypting and decrypting data using the plurality of keys when the user authentication means authenticates the prospective user. The encryption/decryption means is operable in a browser on a client computer.