Abstract: Validating a signed program prior to execution time or an unsigned program at execution time. A program is validated by checking the input parameters to the instructions of the program to prevent errors associated with executing an instruction using an invalid input parameter. Both signed programs and unsigned programs are accommodated. A signed program is validated during the signing process, whereas an unsigned program is validated at execution time.

Abstract: This invention concerns a system and method for securely distributing subsetted fonts from a distributor to a client. The system includes a signing module to construct an authentication tree having leaves formed of glyphs, one or more intermediate levels of nodes computed as one-way functions of the glyphs, and a root computed as a one-way function of the nodes. The signing module digitally signs the root of the authentication tree using a private signing key unique to the font creator or distributor. The system has a subsetting module to construct a font subset file that contains selected glyphs and other data to be included in a font subset. The font subset file also holds the digitally signed root of the font authentication tree and one or more authentication values of the authentication tree that represents non-selected glyphs and data of the font that are not contained in the font subset. The font subset file is distributed to requesting clients.