7. A method comprising the following steps: receiving a font subset that is subsetted from a font file, the font file being represented by an authentication tree whose root is digitally signed by a source; receiving at least one authentication value from the authentication tree that represents portions of the font that are not contained in the font subset; receiving the digitally signed root; reconstructing the authentication tree from the font subset and the authentication value(s); and authenticating the font subset based upon the reconstructed authentication tree and the digitally signed root.
8. A method as recited in claim 7, wherein the authenticating step comprises the following steps: producing an unsigned root from the signed root; deriving a reconstructed root from the reconstructed authentication tree; comparing the reconstructed root with the unsigned root; and accepting the font subset as authentic if the reconstructed root matches the unsigned root.