Cryptography is defined as the art
and science of secret writing. The word itself comes from Greek where the words
kruptos (κρυπτοσ) and graphen (ϒραφην) mean secret and writing, respectively. The
focus in cryptography is to protect the content of the message and to keep it
secure from unintended audiences.
The purpose of cryptography is to
create schemes or protocols which can still complete the intended tasks even in
the presence of an adversary. Cryptography’s main task is to ensure users able
to communicate securely over an insecure channel. This communication however
must ensure the transmission’s privacy and authenticity. [1]
Steganography is the art and
science of hiding information in ways that prevent the detection of hidden
messages. Steganography literally means “covered writing” and is usually
interpreted to mean hiding information in other information. Comparing it to
cryptography, steganography has its advantage because the message itself will
not attract the audiences, as the very nature of a steganography system is to
hide the message in an imperceptible manner.
Another definition given for
steganography is “hiding in plain sight”. The message is still in the open, but
it goes undetected because the existence of the message itself is a secret. It
is explained as a communication that takes place in open, but unless they are
in the know (the sender or recipient), the message goes unnoticed. [2]
Watermarking is the process of
embedding a message on a host signal. Watermarking, as opposed to steganography, has the additional
requirement of robustness against possible attacks. A watermark can be either
visible or invisible.
Using digital watermarking,
copyright information can be embedded into the multimedia data. This is done by
using some algorithms. Information such the serial number, images or text with
special significance can be embedded. The function of this information can be
for copyright protection, secret communication, authenticity distinguish of
data file, etc. [3]
In cryptography, the message
is usually scrambled and unreadable. However, when the communication happens,
it is known or noticed. Although the information is hidden in the cipher, an
interception of the message can be damaging, as it still shows that there is
communication between the sender and receiver. In contrast, steganography takes
a different approach in hiding the evidence that even a communication is taking
place.[2]
Some of the differences between
steganography and watermarking are [4]:
- the information hidden by a watermarking system is always associated to the digital object to be protected or to its owner while steganographic systems just hide any information
- “robustness” criteria are also different, since steganography is mainly concerned with detection of the hidden message while watermarking concerns potential removal by a pirate
- steganographic communications are usually point-to-point (between sender and receiver) while watermarking techniques are usually one-to-many
References:
- Coron, J.-S., What is cryptography? IEEE Security and Privacy, 2006. 4(1): p. 70-73.
- Wiles, J. and R. Rogers, Techno Security's Guide to Managing Risks for IT Managers, Auditors, and Investigators. Security & Networking. 2007: Syngress. 1.
- Jiang, X. Digital watermarking and its application in image copyright protection. in 2010 International Conference on Intelligent Computation Technology and Automation, ICICTA 2010, May 11, 2010 - May 12, 2010. 2010. Changsha, China: IEEE Computer Society.
- Stefan Katzenbeisser, Fabien A. P. Petitcolas, “Information Hiding Techniques for Steganography and Digital Watermarking”, 2000, pp. 2.
