#OUTGUESS ORIGINAL HOW TO#

The basic premise of lossy compression (as is used for media files, e.g. a photograph), then steganography will be possible and very hard to detect, even if the method is completely known (because nothing looks more like random noise than random noise).Ī common tool against steganography is compression. A consequence is that if the medium is in a format which 'naturally' allows for some random noise to appear (e.g. Thus, a good steganography tool will begin by an encryption layer. The message recipient, of course, knows the decryption key: it is part of the secret convention.

#OUTGUESS ORIGINAL HOW TO#

The recipient of the data must know that there is a hidden message, and how to find it.Īmong the tools for steganography, an important one is encryption: symmetric encryption has the ability to transform arbitrary data into a sequence of bits which will have the same probability distribution as random noise. That variability must not alter the apparent meaning of the data.Ī secret convention. If the complete message format is fixed down to the last bit, then there is no way to include an extra message. There must be some room for encoding the hidden message. This implies that no 'universal test' for steganography is currently known - and it is not known whether such a test is even possible. However, no proof (constructive or not) of the impossibility of steganography is currently known. A 'universal test' for steganography would be a constructive proof that steganography is not possible. The whole point of steganography is to avoid detection. This is in fact the problem that 'secret' digital watermarks have versus visible digital watermarks. Of course the scanner doesn't have to be passive if the scanner has the authority to alter images! If it can alter images, it can simply mangle the least significant bit range to destroy any steganographic data without needing to know if there was any.Įven saving from one lossy format to another can mangle the least significant bit range.

photo of fireworks at night) is suspect, the image can be flagged as possibly altered. So if the histogram for that class of image (e.g. That is, due to the pseudo-random nature of most encryption protocols of a steganographic toolkit instead of natural CCD noise.Īnd often even if the exact pre-altered original image isn't available, the scanner does have a database of similar images and histogram profiles. If the steganographic tool didn't perform histogram analysis on the noise patterns of the least significant bits and then adjust the secret payload accordingly (with a corresponding reduction of max payload size) - then a scanner can simply check for least significant bits that are too random. The 'least significant' bits (actual bits will depend on codec) are overwritten by an encrypted stream of secondary 'stego' bits such that the primary public content of the image is not destroyed or distorted with notable artefacts. Steganography relies on the latent noise-to-signal ratio of the analogue source material.

Outguess original