Databases Reference
In-Depth Information
•
the cost to produce such an un-watermarked derivate
Y
of
X
that is still
valuable (with respect to
X
) is higher than its value
Newspaper Digests
To achieve the above however, Alice could publish a summary or digest (e.g.,
cryptographic hash) of
X
in a newspaper, thus being able to claim later on
at least a time-stamp on the possession of
X
. This could apparently result in
a quite effective, albeit costly, alternative to Watermarking the Work
X
.
There are many simple reasons why it would not work, including (i) scal-
ability issues associated with the need for a trusted third party (newspaper),
(ii) the cost of publishing a digest for each released Work, (iii) scenarios when
the fact that the Work is watermarked should be kept secret (stealthiness)
etc.
Maybe the most important reason however, is that Mallory can now claim
that his ownership of the Work precedes
X
's publication date, and that Alice
simply modified it (i.e., a stolen copy) and published a digest thereof herself.
It would then be up to the court to decide if Mallory is to be believed or
not, hardly an encouraging scenario for Alice. This could work if there existed
a mechanism for the mandatory publication of digests for each and every
valuable Work, again quite likely impractical due to both costs and lack of
scalability to a virtually infinite set of data producers and Works.
Deploying such aids as rights assessment tools makes sense only in the
case of the Work being of value only un-modified. In other words if it does
not tolerate any changes, without losing its value, and Mallory is caught in
possession of an identical copy, Alice can successfully prove in court that she
possessed the original at the time of its publication (but she cannot prove
more). Considering that, in the case of watermarking, the assumption is that,
no matter how small, there are modifications allowed to the Works to be
protected, in some sense the two approaches complement each other. If no
modifications are allowed, then a third-party “newspaper” service might work
for providing a time-stamp type of ownership proof that can be used in court.
Steganography and Watermarking
There exists a fundamental difference between Watermarking and generic In-
formation Hiding (steganography) from an application perspective and asso-
ciated challenges. Information Hiding in general (and covert communication
in particular), aims usually at enabling Alice and Bob to exchange messages
in a manner as resilient and stealthy as possible, through a hostile medium
where Malory could lurk. On the other hand, Digital Watermarking is de-
ployed by Alice as a court proof of rights over a Work, usually in the case
when Mallory benefits from using/selling that very same Work or maliciously
modified versions of it.
