Topic: F5—A Steganographic Algorithm High Capacity Despite Better Steganalysis
作者: Andreas Westfeld


Abstract:

Many steganographic systems are weak against visual and
statistical attacks. Systems without these weaknesses offer only a rela-
tively small capacity for steganographic messages. The newly developed
algorithm F5 withstands visual and statistical attacks, yet it still of-
fers a large steganographic capacity. F5 implements matrix encoding to
improve the efficiency of embedding. Thus it reduces the number of nec-
essary changes. F5 employs permutative straddling to uniformly spread
out the changes over the whole steganogram.

本篇論文是Andreas Westfeld所撰，發表在2001年的Information Hiding。
由於許多的資訊隱藏系統無法躲過visual attack 和 statistical attack。而那些可以避免被visual attack 和 statistical attack 偵測出的方法又只能嵌入少量的資訊。本篇論文提出了一種嵌入資訊量大而且不會被visual attack 和 statistical attack兩種方法偵測的steganography 作法 – F5。F5的作法使用了metrix encoding這個方法可以在掩護影像裡減少不必要改變情況下提高遷入的資訊量。這個方法將遷入的資訊散佈在整張偽裝影像中。

• Note

• visual attack 和 statistical attack 的差別在於一個由程式自動判別一個靠人眼去判別
• 現在JPEG上的steganalysis 基本上都是算statistical attack,因為在JPEG上的data hiding基本上都是藏在頻率域 而人眼能看到的影像都是空間域
  

[paper] Defending Against Statistical Steganalysis

Topic: Defending Against Statistical Steganalysis
Abstract:
The main purpose of steganography is to hide the
occurrence of communication. While most methods
in use today are invisible to an observer’s senses,
mathematical analysis may reveal statistical anoma-
lies in the stego medium. These discrepancies ex-
pose the fact that hidden communication is hap-
pening.
This paper presents improved methods for informa-
tion hiding. One method uses probabilistic em-
bedding to minimize modifications to the cover
medium. Another method employs error-correcting
codes, which allow the embedding process to choose
which bits to modify in a way that decreases the
likelihood of being detected. In addition, we can
hide multiple data sets in the same cover medium
to provide plausible deniability.
To prevent detection by statistical tests, we preserve
the statistical properties of the cover medium. After
applying a correcting transform to an image, sta-
tistical steganalysis is no longer able to detect the
presence of steganography. We present an a priori
estimate to determine the amount of data that can
be hidden in the image while still being able to main-
tain frequency count based statistics. This way, we
can quickly choose an image in which a message of
a given size can be hidden safely. To evaluate the
effectiveness of our approach, we present statistical
tests for the JPEG image format and explain how
our new method defeats them.


Niels Provos在2001年於10th USENIX Security Symposium發表的“Defending Against Statistical Steganalysis”中提出兩種資訊隱藏的方法，第一個方法是，在PRNG中選取不同的Redundant Bits位置組合，取掩護媒體改變機率最小的組合來藏資訊，讓cover medium 不要改變太多，第二個方法則是error-correcting codes,，將一半的redundant bits用來維持cover-mediun的統計資訊，priori estimate可以快速的算出在維持frequency count based statistic的情況下掩護影像可遷入的最大資訊量，如此一來可以根據message挑選出適當的掩護影像。本篇論文亦刊於2001年的CITI Tech report。

以下是細看的筆記啦

我看過的paper很少
不知道是我沒注意還是真的之前的都沒有提到
原來steganography 也是有分成classical和modern的
雖然之前有看到Modern 這個字在paper上出現
但是我都以為只是某種方法的改進
沒想到和物理有分成古典物理和近代物理一樣
steganography 也是有分成classical和modern的
真是酷斃了
好
我下一篇的paper要看這兩個的比較