Audio or other information is delivered to a user via a multi-stream
digital broadcasting system in a partially-encrypted form. The
information is encoded and separated into multiple bitstreams, at least a
subset of which are left unencrypted. Both the encrypted and unencrypted
bitstreams are received and stored by the user. A user is able, for at
least a limited period of time, to access the information at a first
quality level, e.g., an FM-quality level for audio information, without
having the corresponding decryption key, by utilizing only the
unencrypted bitstreams. The user can then access an electronic-commerce
web site to purchase the decryption key. The key may be downloaded from
the site to an information processing device of the user, and may be
utilized to decrypt the partially-encrypted format, such that the user is
provided with access to the information at a second quality level higher
than the first quality level, e.g., a CD-quality level for audio
information. The multiple bitstreams may correspond, e.g., to subbands of
at least first and second digital sidebands of a host carrier signal in
an FM in-band on-channel (FM-IBOC) digital audio broadcasting system.