The purpose of steganography is to conceal the very presence of secret information.

剛剛收到的 空中英語教室電子報 200 期, 內容剛好是在討論 very 的形容詞用法, 內容如下:

The U.N.'s Law of the Sea Treaty aims to resolve this very question. (p. 50, line 2)

句中的 very 是形容詞、比較不常見的用法，它有「正是」的強調意味。

例句：

-- The topic you brought up is the very thing we discussed at our last meeting.

-- Barbara realized that her children had done the very thing she feared: they had all moved far from home.

在我的印象中, 我所讀的 steganography papers 中, 的確常常出現這樣的用法:

例如, 在 Jessica Fridrich 所寫的論文 "A New Steganographic Method for Palette-Based Images" 的 Introduction 中, 第二句就是這樣用的:

The purpose of steganography is to conceal the very presence of secret information.

From StegoRN

另外, 在 The Code Breakers 這本書中, Chapter 16 CENSORS, SCRAMBLERS, AND SPIES (P. 513) 中的第一段也有這樣的用法:

CIPHER IS THE LANGUAGE OF SPIES - and usually they must talk in whispers. A spy's success, his very existence, depends on his not being seen or heard. Sending messages in obviously cryptographic form would alert counterespionage to him as effectively as wearing a cloak and dagger. Yet he must transmit, else he is useless. So he eschews the overt methods of secret communications for the covert. He resorts to open codes, hollow heels, invisible inks, microscopically small missives - the steganographic methods that conceal the very fact that a message is being sent. He seeks to communicate unnoticed.

From StegoRN

最近在看的這本書 "Steganography in Digital Media" 中, 第 2 頁的第 2 段, 也是有相同的用法:

Note that the hidden message is unrelated to the content of the letter, which only serve as a decoy or "cover" to hide the very fact that a secret message is being sent. ...

如果你用 "to conceal the very existence" 當關鍵字在 Google 中搜尋, 相信也可以搜尋到許多 steganography 相關的論文或文章呢!

I have received the steganography book!

今天下午, 在 Book Depository 訂購的書, 已經從英國(U.K.) 寄到家裏(Taiwan)了, 剛好花了一個星期的時間!



全球免運費(Free delivery worldwide)的情況下, 還可以在一個星期內拿到書, Book Depository 真的是不簡單!


這本書的封面設計的很不錯! (July 28, 2010)

Book: Steganography in Digital Media

From StegoRN

前幾天在 博客來網路書店 用關鍵字 steganography 搜尋, 竟然讓我找到這本 Jessica Fridrich 在去年底發表的新書, 看了實在很心動, 但原價 85 美元的書, 竟然定價為 3825 元, 匯率竟然是用 45 元計價, 實在是賣得太貴了!

接著, 我就到 金石堂網路書局 去找同樣一本書, 結果金石堂更誇張, 賣 4760 元, 匯率竟高達 56 元。

或許這兩家書局還要負擔從國外寄書進口的運費, 我們就從 Amazon 網路書局來比較一下好了。

這本書在 Amazon 的定價(List Price) 為 85 美元, 實際售價(Price) 為 68 美元, 這本書在美國為 FREE with Super Saver Shipping 免運費, 寄到台灣則是要加上約 10 美元的運費 (Per Shipment 4.99 + Per Item 4.99), 直接從 PayPal 或用信用卡付費, 以目前一美元不到 35 美元的匯率, 頂多 2730 元就搞定了!

當天晚上, 我在 Plurk 發了一則噗, 小小埋怨了一下, 後來一位 噗友 pirrer 建議我試試 Book Depository 這家 UK 網站, 全球免運費。



全球免運費(Free delivery worldwide), 真的讓我很心動! 因此, 在我把 PayPal 帳戶中的信用卡相關資料及地址更新後, 我就直接下單了, 買了 2 本, 一本自己看, 一本給研究生研讀。

接下來, 就要等看看書要幾天才會從 UK 寄來了!

好期待！

Bivariate Distribution & Marginal Distribution

Bivariate Distribution 顧名思義就是具有兩個隨機變數的分配。

From StegoRN

在 貓頭鷹出版社 所出版的 統計學辭典 中, 舉的例子非常容易理解: 特定構造與型示的二手車。一般來說, 對有興趣的買主來說, 二手汽車有兩個令人感興趣且容易測量的變數: 車齡 和 里程數。

假設有一家二手車行購進了同一樣式的二手車 30 輛, 車行就可以將其依車子的使用年齡和行駛里程數製成一個二變量次數表。換句話說, 就是列出一個二維表格, 一維是車齡, 另一維是里程數, 表中統計符合條件的車輛數。例如: 使用 2-3 年, 行駛 4-5 萬英里的車子有 2 輛。在這個例子中, 兩個變數並不是相互獨立的, 較舊的車通常行駛較長的距離。

From StegoRN

如果表中所使用的是機率, 那就是一個 二變量機率分布 (bivariate probability distribution), 在二變量分配表上, 分別做行相加, 或列相加的動作, 所得出的分配就稱為 邊際分配 (marginal distribution)。

在二手車的例子中, 邊際分配為:
里程數　 0-10　10-20　20-30　30-40　40-50　50-60　60-70　70-80
車輛數　　1　　　2　　　2　　　3　　　7　　　6　　　6　　　3

車　齡　 0 - 1 　 1 - 2 　 2 - 3 　 3 - 4 　 4 - 5 　 5 - 6 　 6 - 7 　 7 - 8
車輛數　　3　　　2　　　7　　　9　　　3　　　3　　　1　　　2

維基百科中的 聯合分布 ( joint probability distribution ) 條目的說明, 其實和這邊的 Bivariate Distribution 的解釋是差不多的, 指的應該就是同樣的東西。

Null Cipher in Chinese Medicine History

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

Book: INFORMATION HIDING techniques for steganography and digital watermarking

From StegoRN

Editors: Stefan Katzenbeisser & Fabien A. P. Petitcolas
ARTECH HOUSE, Computer Security Series
ISBN 1-58053-035-4
(Available on Amazon.com)

This book surveys recent research results in the fields of watermarking and steganography, two disciplines generally referred to as information hiding. Included are chapters about the following topics:

* Chapter 1: Introduction to information hiding
(Fabien A. P. Petitcolas) gives an introduction to the field of information hiding, thereby discussing the history of steganography and watermarking and possible applications to modern communication systems.
* Chapter 2: Principles of steganography
(Stefan Katzenbeisser) introduces a model for steganographic communication (the ‘prisoners problem") and discusses various steganographic protocols (such as pure steganography, secret key steganography, public key steganography and supraliminal channels).
* Chapter 3: A survey of steganographic techniques
(Neil F. Johnson and Stefan Katzenbeisser) discusses several information hiding methods useable for steganographic communication, among them substitution systems, hiding methods in two-colour images, transform domain techniques, statistical steganography, distortion and cover generation techniques.
* Chapter 4: Steganalysis
(Neil F. Johnson) introduces the concepts of steganalysis – the task of detecting and possibly removing steganographic information. Included is also an analysis of common steganographic tools.
* Chapter 5: Introduction to watermarking techniques
(Martin Kutter and Frank Hartung) introduces the requirements and design issues for watermarking software. The authors also present possible applications for watermarks and discuss methods for evaluating watermarking systems.
* Chapter 6: A survey of current watermarking techniques
(Jean-Luc Dugelay and Stéphane Roche) presents several design principles for watermarking systems, among them the choice of host locations, psychovisual aspects, the choice of a workspace (DFT, DCT, wavelet), the format of the watermark bits (spread spectrum, low-frequency watermark design), the watermark insertion operator and optimizations of the watermark receiver.
* Chapter 7: Robustness of copyright marking systems
(Scott Craver, Adrian Perrig and Fabien A. P. Petitcolas) discusses the crucial issue of watermark robustness to intentional attacks. The chapter includes a taxonomy of possible attacks against watermarking systems, among them protocol attacks like inversion, oracle attacks, limitations of WWW spiders and system architecture issues.
* Chapter 8: Fingerprinting
(Jong-Hyeon Lee) discusses principles and applications of fingerprinting to the traitor tracing problem, among them statistical fingerprinting, asymmetric fingerprinting and anonymous fingerprinting.
* Chapter 9: Copyright on the Internet and watermarking
(Stanley Lai and Fabrizio Marongiu Buonaiuti) finally discusses watermarking systems from a legal point of view and addresses various other aspects of copyright law on the Internet.

Null Cipher

A null cipher hides the message according to some prearranged set of rules, such as "read every fifth word" or "look at the third character in every word."

一次世界大戰 (WWI) 期間, 一名德國間諜利用 Null Cipher 的方式, 從美國 Washington, D.C. 向位於 Berlin 總部回報了底下這段文字:

PRESIDENT'S EMBARGO RULING SHOULD HAVE IMMEDIATE NOTICE. GRAVE SITUATION AFFECTING INTERNATIONAL LAW. STATEMENT FORESHADOWS RUIN OF MANY NEUTRALS. YELLOW JOURNALS UNIFYING NATIONAL EXCITEMENT
IMMENSELY.

為求慎重, 又發了底下一段文字, 作為確認 (check) 之用:

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)。



上述這個 Null Cipher Message 的例子, 最早我是在 IEEE Computer, February 1998 這期 Neil F. Johnson 與 Sushil Jajodia 的文章 "Exploring Steganography: Seeing the Unseen" 所讀到。

今天, 我在 WebStone 公司的 Stego Suite 網頁所提供的技術論文 "What You Can't See Can Hurt You" (2002), 又讀到了相同的例子。

不過, 上述兩篇論文都把故事發生的時間誤寫成 WWII, 發現這點是因為我後來研讀 Gray C. Kessler 的論文 "An Overview of Steganography for the Computer Forensics Examiner" [ PDF ] 時, 也讀到了這段故事, 不過故事發生的時間卻是在 WWI, 與上述兩篇所寫的 WWII 有出入。

From StegoRN

因此, 我就去翻這些論文的原始參考文獻 "THE CODE BREAKERS - The Comprehensive History of Secret Communication from Ancient Times to the Internet" (David Kahn, 1996), 終於確認時間應該是 WWI。

有趣的是書中 (P. 521) 還提到 Pershing 確實出發的日期應該是 May 28, 而不是 June 1, 顯然這位德國間諜情報有誤, 搞了一次烏龍。