Patent ID: 7165179

Claim:
A proxy server for relaying communications between applications and for performing an additional process comprising: a key manager for managing multiple keys used to generate a digital signature to be provided for a message document that is exchanged between said applications, wherein each of said multiple keys is used to sign messages having particular message contents; a signature key determiner for extracting said message document from a predetermined application, and for, based on the contents of said message document, determining a selected key from said multiple keys that is to be used to provide a digital signature, wherein said contents do not include any digital signature data; and a signature generator for providing a digital signature for said message document by using said key selected that is obtained from said key manager based on a determination made by said signature key determiner, and for transmitting said message document with said digital signature to a destination application, wherein said key manager sets multiple key selection rules and only when said key selection rules are satisfied can said signature generator obtain said selected key, and wherein, when said selected key for generating a digital signature for said message document can not be obtained, said signature generator employs a predetermined replacement key to provide a digital signature, and wherein, after said signature generator has provided a digital signature using said replacement key, when said selection rules are satisfied to enable the acquisition of said selected key, said signature generator again provides a digital signature using said selected key.