A cryptographic apparatus reads, from a portable storage medium, content data and cryptographic information specifying a certain part of the content data on which cryptographic processing is to be performed, specifies the certain part in the read content data based on the read cryptographic information,...http://www.google.com.au/patents/US6971022?utm_source=gb-gplus-sharePatent US6971022 - Cryptographic apparatus for performing cryptography on a specified area of content data
