OutGuess
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| OutGuess | |
|---|---|
| Original author | Niels Provos |
| Initial release | 1999 |
| Stable release | 0.4[1]
/ 2 September 2021 |
| Repository | |
| Written in | C |
| Operating system | Windows, Unix-like |
| Type | steganography |
| License | BSD (Free Software) |
OutGuess is a steganographic software. It has handlers for image files in the common Netpbm and JPEG formats, so it can, for example, specifically alter the frequency coefficients of JPEG files. It is written in C and published as Free Software under the terms of the old BSD license. It has been tested on a variety of Unix-like operating systems and is included in the standard software repositories of the popular Linux distributions Debian and Arch Linux (via user repository) and their derivatives.
An algorithm estimates the capacity for hidden data without the distortions of the decoy data becoming apparent. OutGuess determines bits in the decoy data that it considers most expendable and then distributes secret bits based on a shared secret in a pseudorandom pattern across these redundant bits, flipping some of them according to the secret data. For JPEG images, OutGuess recompresses the image to a user-selected quality level and then embeds secret bits into the least significant bits (LSB) of the quantized coefficients while skipping zeros and ones.[2] Subsequently, corrections are made to the coefficients to make the global histogram of discrete cosine transform (DCT) coefficients match that of the decoy image, counteracting detection by the chi-square attack that is based on the analysis of first-order statistics.[citation needed] This technique is criticized because it actually facilitates detection by further disturbing other statistics.[3] Also, data embedded in JPEG frequency coefficients has poor robustness and does not withstand JPEG reencoding.[4][citation needed]