The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
May. 16, 2000
Filed:
Oct. 01, 1997
Daniel R Simon, Redmond, WA (US);
Josh Benaloh, Redmond, WA (US);
Donald D Chinn, Redmond, WA (US);
Gregory Hitchcock, Woodinville, WA (US);
David Meltzer, Seattle, WA (US);
Microsoft Corporation, Redmond, WA (US);
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. An authentication module at the client authenticates the font subset file received from the distributor. The authentication module reconstructs the root of the authentication tree using the selected glyphs and data in the font subset and the authentication values that represent the non-selected glyphs and data not contained in the font subset. The authentication module also produces an unsigned version of the digitally signed root using a public key of the font creator to produce an unsigned root digest. The authentication module compares the unsigned root to the reconstructed root and if and only if they match, authenticates the font subset file as originating from the distributor (or font creator) and not being subsequently altered.