15. A system for supplying authenticated font subsets, comprising: a signing module to construct an authentication tree for a font and digitally signing a root of the authentication tree; a subsetting module to subset the font to form a font subset and constructing a font subset file containing the font subset, the digitally signed root, and at least one authentication value of the authentication tree that represents portions of the font that are not contained in the font subset; and an authentication module to authenticate the font subset by reconstructing the root of the authentication tree using the font subset and the authentication value(s) from the font subset file, producing an unsigned root from the digitally signed root of the font subset file, and checking the unsigned root against the reconstructed root.
15. A system for supplying authenticated font subsets, comprising: a signing module to construct an authentication tree for a font and digitally signing a root of the authentication tree; a subsetting module to subset the font to form a font subset and constructing a font subset file containing the font subset, the digitally signed root, and at least one authentication value of the authentication tree that represents portions of the font that are not contained in the font subset; and an authentication module to authenticate the font subset by reconstructing the root of the authentication tree using the font subset and the authentication value(s) from the font subset file, producing an unsigned root from the digitally signed root of the font subset file, and checking the unsigned root against the reconstructed root. 18. A system as recited in claim 15, further comprising: a source computer residing at a font creator, the signing module being configured as a software component executing on the source computer; a distributor computer residing at a font distributor, the subsetting module being configured as a software component executing on the distributor computer; and a recipient computer residing at a recipient, the authentication module being configured as a software component executing on the recipient computer.