Bar analysis
The Steganalysis - formed as a suitcase word from Stegan ography and to alyse - deals with the analysis and breaking steganographic methods.
Differentiation from cryptanalysis
Steganography is used to hide secret data , while cryptography is used to encrypt secret data . Accordingly, cryptanalysis deals with methods and techniques to extract information from encrypted texts. It is known that the information is encrypted.
In contrast to this , one only suspects with the web analysis that data is hidden in a carrier medium. Therefore, the initial aim is not to read out a hidden message, but rather to prove that a message is actually present. If the embedding of data in a carrier medium is viewed as a form of manipulation, the bar analysis can be understood as a special case of multimedia forensics .
The bar analysis uses, among other things, findings from cryptanalysis.
Methods of bar analysis
In the bar analysis, a message is assumed to be in a medium . The security of steganography is based on the fact that third parties do not notice its use (confidentiality). Another, but not mandatory, point is that a recognized use of steganography does not automatically lead to legibility of the message (confidentiality).
The bar analysis therefore proceeds in two steps:
- Find out whether a medium can contain steganographic information at all, and if this cannot be ruled out
- Analyze, recognize and extract the steganographic information
Focus
There are several areas of focus:
Recognizability
In the recognition of a steganographic information in a steganogram it is assumed that an observed medium does not contain any message or embedding steganographic (null hypothesis). So the alternative thesis that one is trying to prove is that it is a steganogram. As is usual with statistical tests , the result is only an indicator that says with a certain probability whether the alternative hypothesis is true or not. If it does not apply, however, this is not proof that the medium is without secret information. Rather, the result then only states that it was not possible with the test carried out to prove the use of steganographic methods. There is always the possibility that another test will provide evidence.
The detectability does not depend on the knowledge of the exact algorithm. As a rule, clearly categorized carrier media ( test samples ) in both steganographically modified and unchanged form are sufficient to carry out corresponding tests.
extraction
When extracting steganographic information, information is obtained from the steganogram that was only intended for the recipient of the steganographic message. If extraction is possible, the corresponding process is considered broken.
Digital watermarks
Bar analysis methods are also used in the field of digital watermarks . It is known to contain hidden information. In this variant of the web analysis, an attempt is made to read, manipulate or delete the digital watermark from the medium (image, video or audio) and, under certain circumstances, to otherwise leave the carrier medium intact.