| From StegoRN |
上個星期逛台北捷運的地下書街, 看到了這本《中醫藥典故與傳說》, 第七章的醫家軼聞, 我首先閱讀了我較為熟悉的醫聖張仲景部份, 其中有一個故事就是張仲景利用 Null Cipher 這樣的技術巧戲庸官, 故事中的方子如下:
柏子仁三錢
木瓜二錢
官桂二錢
柴胡三錢
益智二錢
附子二錢
八角二錢
人蔘一錢
台烏三錢
上党三錢
山藥二錢
| From StegoRN |
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| From StegoRN |
| Paper submission deadline: | March 30th, 2007 |
| Notification of Acceptance: | May 14th, 2007 |
| Camera ready paper: | June 4th, 2007 |
p2. left column本篇論文的核心觀念描述在底下這段文字:
The OutGuess steganographic algorithm was proposed by Neils Provos to counter the statistical chi-square attack. In the first pass, similar to J-Steg, OutGuess embeds message bits along a random walk into the LSBs of coefficients while skipping 0’s and 1’s. After embedding, the image is processed again using a second pass. This time, corrections are made to the coefficients to make the stego image histogram match the cover image histogram. Because the chi-square attack is based on analyzing first-order statistics of the stego image, it cannot detect messages embedded using OutGuess. Provos also reports that the corrections are made in such a manner to avoid detection using his generalized chi-square attack.
P.2 right column由於 OutGuess 隨機改變量化後 DCT 係數的 LSBs, 增加了還原後 8*8 區塊的不連續性。J. Fridrich用一個 blockiness formula 來估算區塊不連續性。使用 OutGuess 藏入100% 的資料量後, 檢驗區塊不連續性的增加量。如果這張影像是偽裝影像(stego image), 區塊不連續性增加量是比原始掩護影像 (cover image) 來得小。這個差距就是用來估算嵌入資料量的基礎。
Because OutGuess introduces random changes into the quantized coefficients, the spatial discontinuities at the boundaries of all 8×8 blocks will increase. We will measure the discontinuity using the blockiness measure. For detection, we will inspect the increase of this blockiness measure after embedding a 100% message again using OutGuess. This increase will be smaller for the stego image than for the cover image because of the partial cancellation of changes. This difference will form the basis of our message length estimation.
steganographysteganography 在 Merrian-Webster Online 的連結網址是 http://www.m-w.com/dictionary/steganography\steg-uh-NAH-gruh-fee\ noun
: the art or practice of concealing a message, image, or file within another message, image, or file
Example sentence:
No doubt, the Internet has enriched society, but it has a flip side; terrorists, for instance, can secretly network online using steganography.
Did you know?
"Steganography" is a word that was resurrected after being in disuse for almost 150 years! It was put to rest in the early 1800s, labeled an archaic synonym of "cryptography" by dictionary makers, but was brought back to life in the 1980s as a word for a type of digital cryptography. There is nothing cryptic about the word's origin; it is based on the Greek word "steganos," meaning "covered" or "reticent."
Main Entry: steg·a·nog·ra·phy相對於 cryptography 的 steganography, Merrian-Webster Online 已經有解釋了, 不過, 相對於cryptanalysis 的 steganalysis, 不曉得還要等多久, 字典的解釋才會補上來...
Pronunciation: "ste-g&-'nä-gr&-fE
Function: noun
Etymology: New Latin steganographia, from Greek steganos covered, reticent (from stegein to cover) + Latin -graphia -graphy -- more at THATCH
1 archaic : CRYPTOGRAPHY
2 : the art or practice of concealing a message, image, or file within another message, image, or file
- steg·a·no·graph·ic/-n&-'gra-fik/ adjective

PRESIDENT'S EMBARGO RULING SHOULD HAVE IMMEDIATE NOTICE. GRAVE SITUATION AFFECTING INTERNATIONAL LAW. STATEMENT FORESHADOWS RUIN OF MANY NEUTRALS. YELLOW JOURNALS UNIFYING NATIONAL EXCITEMENT為求慎重, 又發了底下一段文字, 作為確認 (check) 之用:
IMMENSELY.
APPARENTLY NEUTRAL'S PROTEST IS THOROUGHLY DISCOUNTED AND IGNORED. ISMAN HARD HIT. BLOCKADE ISSUE AFFECTS PRETEXT FOR EMBARGO ON BYPRODUCTS, EJECTING SUETS AND VEGETABLE OILS.如果我們第一段訊息中, 每個字的第一個字母抽出, 或是將第二段訊息中, 每個字的第二個字母抽出, 都可以發現底下的句子:
Pershing sails from NY June 1.John J. Pershing 是一次大戰期間, 美國遠征軍 (American Expeditionary Force) 的指揮官, 也是二次大戰期間, 美國將領們的良師(mentor)。
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| From StegoRN |
JPHIDE and JPSEEK are programs which allow you to hide a file in a jpeg visual image. There are lots of versions of similar programs available on the internet but JPHIDE and JPSEEK are rather special. The design objective was not simply to hide a file but rather to do this in such a way that it is impossible to prove that the host file contains a hidden file. Given a typical visual image, a low insertion rate (under 5%) and the absence of the original file, it is not possible to conclude with any worthwhile certainty that the host file contains inserted data. As the insertion percentage increases the statistical nature of the jpeg coefficients differs from "normal" to the extent that it raises suspicion. Above 15% the effects begin to become visible to the naked eye. Of course some images are much better than others when used a host file - plenty of fine detail is good. A cloudless blue sky over a snow covered ski paradise is bad. A waterfall in a forest is probably ideal.其大意是這樣的:
JPHIDE and JPSEEK 是一個可以將檔案藏進 JPEG 影像的程式。在 Internet 上, 有許多類似程式及其各種版本, 然而, JPHIDE and JPSEEK 卻相當特別!JPHIDE and JPSEEK 的設計目的並不僅是簡單地隱藏檔案, 反而是進一步要表達: 要證明某張偽裝影像嵌有檔案是不可能的。給定一個嵌有低嵌入比例 (低於 5% ) 的影像, 在沒有原始影像的情況下, 並沒有辦法去判斷這張影像嵌有訊息的。當嵌入比例增加時, JPEG 係數的統計特性偏離了原來的正常範圍, 就會引起懷疑。超過 15% 的嵌入比例時, 對於影像品質的影響是肉眼可見的。當然, 擁有較多細節的影像是比較適合用來做掩護影像 ( host ) 的。例如: 一張藍天無雲的滑雪天堂的圖片, 就不太適合用來嵌入訊息; 在森林中瀑布拍攝的圖片就是一張理想的掩護影像。JPHIDE and JPSEEK 有兩個版本:
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| From StegoRN |
There are three popular steganographic systems available on the Internet that hide information in JPEG images:
• JSteg, JSteg-ShellAll of these systems use some form of leastsignificant bit embedding and are detectable by statistical analysis except the latest release of OutGuess. In the following, we describe the specific characteristics of these systems and show how to detect them.
Niels Provos and Peter Honeyman, "Detecting Steganographic Content on the Internet,"ISOC NDSS'02, San Diego, CA, February 2002.