Steganography tools - AbsoluteAstronomy.com

Steganography

Steganography is the art and science of writing hidden messages in such a way that no one, apart from the sender and intended recipient, suspects the existence of the message, a form of security through obscurity...

software tool implements a subset of the most general digital steganography process, allowing users to insert and extract hidden data into and from carrier files.

Architecture

Novel users approaching steganography need to get acquainted with some common steganography-related terms and concepts

Hidden data

Data to be covertly communicated are usually referred to as hidden data. Steganography focuses on the covertly adjective. You're going to employ a steganography tool because the very existence of the data has to be secret and invisible. The tool can also perform some cryptography

Cryptography

Cryptography is the practice and study of techniques for secure communication in the presence of third parties...

on the hidden data, but remember it is optional: data has to be invisible first.

Please notice also that, according to common public opinion:

Cryptography plays a relevant role in public / trusted / legal data sharing
Steganography plays a minor role in secret / obscure / illegal data sharing

Carrier

The carrier is the signal, stream, or data file into which the payload is hidden.

Take also a look to this practical definition of carrier:

The audio/image/video/text/executable/repository file that, once processed,
- will look and work as the original one
- will hold inside part of or the whole hidden data
- will raise no suspect sending it by email, sharing it through internet, carrying it out of the office, a.s.o.

From a user point of view:

Carriers have to raise no suspect because of their size
- small carriers with no data are very suspicious: What would you think about an empty word document with a 1Mb size?
- huge carriers exchanged through internet are very suspicious: What about a downloadable set of DVD .vob
  VOB
  A VOB file is a container format in DVD-Video media. VOB can contain video, audio, subtitle, menu and navigation contents multiplexed together into a stream form. VOB is based on the MPEG program stream format, but with additional limitations and specifications in the private streams...
  
  files?
Carriers have to raise no suspect because of their format
- out of date file formats are very suspicious: What about a .wav
  WAV
  Waveform Audio File Format , is a Microsoft and IBM audio file format standard for storing an audio bitstream on PCs...
  
  downloadable telephone ringtone?
- non standard file format extensions are very suspicious: What about a PDF reported as broken or corrupted by adobe reader?

Chain

When hidden data is split among a set of files you get a carrier chain.

Carrier chains are a main feature of every professional steganography tool, ensuring that you can't get the hidden data back:

if one or more carriers are missing
if one or more carriers have been manipulated (volatile steganography)
if one or more carriers are not processed in the correct order

This additional security feature is usually achieved by:

using a different initialization vector
Initialization vector
In cryptography, an initialization vector is a fixed-size input to a cryptographic primitive that is typically required to be random or pseudorandom...

for each carrier and storing it inside processed carriers -> CryptedIVn = Crypt( IVn, CryptedIVn-1 )
using a different cryptography algorithm for each carrier and choosing it with a chain-order-dependent equiprobabilistic
Equiprobable
Equiprobability is a philosophical concept in probability theory that allows one to assign equal probabilities to outcomes when they are judged to be equipossible or to be "equally likely" in some sense...

algorithm

Cryptography

Users have to remember that steganography's main goal is invisibility. A good steganography tool should first ensure robustness against modern forensic methods

Computer forensics

Computer forensics is a branch of digital forensic science pertaining to legal evidence found in computers and digital storage media...

, like statistical steganalysis

Steganalysis

Steganalysis is the art and science of detecting messages hidden using steganography; this is analogous to cryptanalysis applied to cryptography.- Overview :...

. Strong cryptography, along with any other obfuscation process, is always welcome but should only be considered as a last-man-standing defense. Encoding (steganography) will deceive attackers and obfuscation (cryptography) will slow them down once you've been caught. People hiding sensitive data should consider deniable cryptography

Deniable encryption

In cryptography and steganography, deniable encryption is encryption that allows its users to convincingly deny that the data is encrypted, or that they are able to decrypt it. Such convincing denials may or may not be genuine. For example, although suspicions might exist that the data is...

as an exit strategy

Exit strategy

An exit strategy is a means of leaving one's current situation, either after a predetermined objective has been achieved, or as a strategy to mitigate failure. An organisation or individual without an exit strategy may be in a quagmire...

.

Robustness against statistical steganalysis

Steganalysis

Steganalysis is the art and science of detecting messages hidden using steganography; this is analogous to cryptanalysis applied to cryptography.- Overview :...

can be achieved by a balanced mix of:

stream based cryptography process
data whitening
Decorrelation
Decorrelation is a general term for any process that is used to reduce autocorrelation within a signal, or cross-correlation within a set of signals, while preserving other aspects of the signal. A frequently used method of decorrelation is the use of a matched linear filter to reduce the...

process
encoding process

Steganography users should rely only on multi-layered architectures with a deep documented obfuscation

Obfuscation

Obfuscation is the hiding of intended meaning in communication, making communication confusing, wilfully ambiguous, and harder to interpret.- Background :Obfuscation may be used for many purposes...

process.

Carrier engine

The carrier engine is the core of any steganography tool. Different file formats are modified in different ways, in order to covertly insert hidden data inside them. Among these processing algorithms you can find:

Injection (suspicious because of the content-unrelated file size increment)
Generation (suspicious because of the traceability of the generated carriers)
Ancillary data
Ancillary data
Ancillary data , in the context of television systems, refers to a means which by non-video information may be embedded within the serial digital interface...

and metadata
Metadata
The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...

substitution
LSB
Least significant bit
In computing, the least significant bit is the bit position in a binary integer giving the units value, that is, determining whether the number is even or odd. The lsb is sometimes referred to as the right-most bit, due to the convention in positional notation of writing less significant digits...

or adaptive substitution
Frequency space manipulation

Architecture

Hidden data

Carrier

Chain

Cryptography

Carrier engine

See also

Steganography tools directories

Articles

Workshops