An initialization vector (IV) is employed to decrypt a block of a stream
that has been encrypted with Cypher Block Chaining (CBC) encryption,
without requiring decryption of previous blocks within the stream. For
example, a listener who accesses a distribution point to retrieve
encrypted content authenticates himself to an application server that
regulates access to encrypted content on the distribution point, and
responsively receives a key. The listener then requests access to a
reference point within the encrypted content stream somewhere after its
beginning (e.g., using preview clips). The distribution point relates the
reference point to a corresponding block of the encrypted stream, and
identifies an IV previously used for encryption of that block. The
distribution point provides the associated encrypted block of content and
the IV to the listener to enable mid-stream rendering of the encrypted
content, without requiring the listener to decrypt previous blocks within
the encrypted stream.