Another way to distribute electronic books is for publishers to put their entire list on a single disc. Publishers can encrypt each title separately so knowing the decrypt key for a title unlocks that title only. Encryption is different from copy protection; copy protection tries to make information physically uncopyable, encryption tries to make information unintelligible without a key. One tries to lock the hardware, the other tries to lock the software. Both try to deny general access.
These discs can be produced in runs of several thousand at $1 per disc and could be sold for $5 each. As in the subscription scheme, publishers could bypass retailers entirely and sell these discs by mail order. And retailers could increase title diversity by many thousands; even the smallest retailer could carry every book ever written since each publisher only needs one disc. After buying a disc, a reader who wants a particular title phones the publisher and the publisher gives the title's decrypt key then charges the reader's credit card. Such a scheme is already being tried by font and clip-art companies .
State of the art encryption schemes are virtually unbreakable, but once one reader pays for the decrypt key for a particular title that reader could tell the rest of the world. So publishers may divide the print run into lots of 100, number the discs, and change all encrypt keys from one run to the next. This will increase disc production costs and users would have to supply the disc lot number when ordering. As with any protection scheme, cost increases and usability decreases.
Many publishers may choose this scheme since it is most like their present system, but better. Further, each title is protected so publishers could increase prices if they choose. But this scheme, and every other scheme that distributes books on fixed media, has the problems discussed in the overview and in the previous section.