Terror groups hide behind Web encryption
02/05/2001 - Updated 05:17 PM ET
By Jack Kelley
WASHINGTON — Hidden in the X-rated pictures on several pornographic Web sites and the posted comments on sports chat rooms may lie the encrypted blueprints of the next terrorist attack against the United States or its allies. It sounds farfetched, but U.S. officials and experts say it's the latest method of communication being used by Osama bin Laden and his associates to outfox law enforcement. Bin Laden, indicted in the bombing in 1998 of two U.S. embassies in East Africa, and others are hiding maps and photographs of terrorist targets and posting instructions for terrorist activities on sports chat rooms, pornographic bulletin boards and other Web sites, U.S. and foreign officials say.
"Uncrackable encryption is allowing terrorists — Hamas, Hezbollah, al-Qaida and others — to communicate about their criminal intentions without fear of outside intrusion," FBI Director Louis Freeh said last March during closed-door testimony on terrorism before a Senate panel. "They're thwarting the efforts of law enforcement to detect, prevent and investigate illegal activities."
A terrorist's tool
Once the exclusive domain of the National Security Agency, the super-secret U.S. agency responsible for developing and cracking electronic codes, encryption has become the everyday tool of Muslim extremists in Afghanistan, Albania, Britain, Kashmir, Kosovo, the Philippines, Syria, the USA, the West Bank and Gaza and Yemen, U.S. officials say.
It's become so fundamental to the operations of these groups that bin Laden and other Muslim extremists are teaching it at their camps in Afghanistan and Sudan, they add.
"There is a tendency out there to envision a stereotypical Muslim fighter standing with an AK-47 in barren Afghanistan," says Ben Venzke, director of special intelligence projects for iDEFENSE, a cyberintelligence and risk management company based in Fairfax, Va.
"But Hamas, Hezbollah and bin Laden's groups have very sophisticated, well-educated people. Their technical equipment is good, and they have the bright, young minds to operate them," he said.
U.S. officials say bin Laden's organization, al-Qaida, uses money from Muslim sympathizers to purchase computers from stores or by mail. Bin Laden's followers download easy-to-use encryption programs from the Web, officials say, and have used the programs to help plan or carry out three of their most recent plots:
* Wadih El Hage, one of the suspects in the 1998 bombing of two U.S. embassies in East Africa, sent encrypted e-mails under various names, including "Norman" and "Abdus Sabbur," to "associates in al Qaida," according to the Oct. 25, 1998, U.S. indictment against him. Hage went on trial Monday in federal court in New York.
* Khalil Deek, an alleged terrorist arrested in Pakistan in 1999, used encrypted computer files to plot bombings in Jordan at the turn of the millennium, U.S. officials say. Authorities found Deek's computer at his Peshawar, Pakistan, home and flew it to the National Security Agency in Fort Meade, Md. Mathematicians, using supercomputers, decoded the files, enabling the FBI to foil the plot.
* Ramzi Yousef, the convicted mastermind of the World Trade Center bombing in 1993, used encrypted files to hide details of a plot to destroy 11 U.S. airliners. Philippines officials found the computer in Yousef's Manila apartment in 1995. U.S. officials broke the encryption and foiled the plot. Two of the files, FBI officials say, took more than a year to decrypt.
"All the Islamists and terrorist groups are now using the Internet to spread their messages," says Reuven Paz, academic director of the Institute for Counter-Terrorism, an independent Israeli think tank.
Messages in dots
U.S. officials and militant Muslim groups say terrorists began using encryption — which scrambles data and then hides the data in existing images — about five years ago.
But the groups recently increased its use after U.S. law enforcement authorities revealed they were tapping bin Laden's satellite telephone calls from his base in Afghanistan and tracking his activities.
"It's brilliant," says Ahmed Jabril, spokesman for the militant group Hezbollah in London. "Now it's possible to send a verse from the Koran, an appeal for charity and even a call for jihad and know it will not be seen by anyone hostile to our faith, like the Americans."
Extremist groups are not only using encryption to disguise their e-mails but their voices, too, Attorney General Janet Reno told a presidential panel on terrorism last year, headed by former CIA director John Deutsch. Encryption programs also can scramble telephone conversations when the phones are plugged into a computer.
"In the future, we may tap a conversation in which the terrorist discusses the location of a bomb soon to go off, but we will be unable to prevent the terrorist act when we cannot understand the conversation," Reno said.
Here's how it works: Each image, whether a picture or a map, is created by a series of dots. Inside the dots are a string of letters and numbers that computers read to create the image. A coded message or another image can be hidden in those letters and numbers.
They're hidden using free encryption Internet programs set up by privacy advocacy groups. The programs scramble the messages or pictures into existing images. The images can only be unlocked using a "private key," or code, selected by the recipient, experts add. Otherwise, they're impossible to see or read.
"You very well could have a photograph and image with the time and information of an attack sitting on your computer, and you would never know it," Venzke says. "It will look no different than a photograph exchanged between two friends or family members."
U.S. officials concede it's difficult to intercept, let alone find, encrypted messages and images on the Internet's estimated 28 billion images and 2 billion Web sites.
Even if they find it, the encrypted message or image is impossible to read without cracking the encryption's code. A senior Defense Department mathematician says cracking a code often requires lots of time and the use of a government supercomputer.
It's no wonder the FBI wants all encryption programs to file what amounts to a "master key" with a federal authority that would allow them, with a judge's permission, to decrypt a code in a case of national security. But civil liberties groups, which offer encryption programs on the Web to further privacy, have vowed to fight it.
Officials say the Internet has become the modern version of the "dead drop," a slang term describing the location where Cold War-era spies left maps, pictures and other information.
But unlike the "dead drop," the Internet, U.S. officials say, is proving to be a much more secure way to conduct clandestine warfare.
"Who ever thought that sending encrypted streams of data across the Internet could produce a map on the other end saying 'this is where your target is' or 'here's how to kill them'?" says Paul Beaver, spokesman for Jane's Defense Weekly in London, which reports on defense and cyberterrorism issues. "And who ever thought it could be done with near perfect security? The Internet has proven to be a boon for terrorists."
Terrorist instructions hidden online
02/05/2001 - Updated 05:22 PM ET
By Jack Kelley
WASHINGTON — Osama bin Laden and other Muslim extremists are posting encrypted, or scrambled, photographs and messages on popular Web sites and using them to plan terrorist activities against the United States and its allies, U.S. officials say. The officials say bin Laden and his associates are using the Internet to conduct what some are calling "e-jihad," or holy war. Bin Laden, a dissident Saudi businessman, has been indicted for the 1998 bombing of two U.S. embassies in East Africa and is believed to be responsible for last fall's bombing of the USS Cole in Yemen. Four alleged bin Laden associates went on trial Monday in federal court in New York for the embassy bombings. "To a greater and greater degree, terrorist groups, including Hezbollah, Hamas, and bin Laden's al Qaida group, are using computerized files, e-mail, and encryption to support their operations," CIA Director George Tenet wrote last March to the Senate Foreign Relations Committee. The testimony, at a closed-door hearing, was later made public.
Through weeks of interviews with U.S. law-enforcement officials and experts, USA TODAY has learned new details of how extremists hide maps and photographs of terrorist targets — and post instructions for terrorist activities — on sports chat rooms, pornographic bulletin boards and other popular Web sites. Citing security concerns, officials declined to name the sites. Experts say it's difficult for law enforcement to intercept the messages.
"It's something the intelligence, law-enforcement and military communities are really struggling to deal with," says Ben Venzke, special projects director for iDEFENSE, a cyberintelligence company.
Officials and experts say the Internet is a new form of the "dead drop," a Cold War-era term for where spies left information. Officials and experts say the messages are scrambled using free encryption programs set up by groups that advocate privacy on the Internet. Those same programs also can hide maps and photographs in an existing image on selected Web sites. The e-mails and images can only be decrypted using a "private key" or code, selected by the recipient .
"The operational details and future targets, in many cases, are hidden in plain view on the Internet," Venzke says. "Only the members of the terrorist organizations, knowing the hidden signals, are able to extract the information."
Officials say bin Laden began using encryption five years ago, but recently increased its use after U.S. officials revealed they were tapping his satellite telephone calls in Afghanistan and tracking his activities.
"We will use whatever tools we can — e-mails, the Internet — to facilitate jihad against the (Israeli) occupiers and their supporters," Sheik Ahmed Yassin, the founder of the militant Muslim group Hamas said in a recent interview in the Gaza Strip. "We have the best minds working with us."
To evaluate our correction algorithm, we embedded data into 54 pictures taken with a Fuji MX-1700 digital camera around Ann, Arbor, Michigan. The sizes of images is 640*480 pixels.將照片從數位相機下載到電腦後, 作者設定壓縮品質參數為 75, 將影像重新壓縮, 用來模擬沒有嵌入任何機密訊息的影像。
On average 63.8% of all the bits are set with a standard derivation of 3.4% between images.接著, 作者將 Lewis Carroll (愛麗絲夢遊仙境 作者)所著的 "The Hunting of the Snark" 第一章內容 壓縮, 得到 14,700 位元的機密訊息。
Niels Provos, "Defending Against Statistical Steganalysis,"10th USENIX Security Symposium, August 13-17, 2001.
For example, ones and zeros are equally likely in a message that has been encrypted. However, the redundant data being replaced might have a strong correction towards either zero or one. Embedding the encrypted message weakens that correction.Maurer test 則是一個用來測試所產生的二元亂數資料是否符合良好亂數的規範的工具 (Ueli M. Maurer, "A Universal Statistical Test for Random Bit Generators," Journal of Cryptography, Vol. 5, pp 89-105, 1992 )。基本上, 當有一個冗餘位元從 0 被改成 1, 作者便嘗試在附近找到另一個冗餘位元將其從 1 改成 0, 這樣做的優點是可以避免增加冗餘位元的亂度(entropy), 確保機密訊息無法從這種統計方式偵測出來。然而, 使用上述的方法, 針對 JPEG 影像, 會使得 DCT 係數直方圖走樣(distortion), 如 Figure 5 中的 DCT 係數 -2 與 -1 比 Figure 3 更接近, DCT 係數 2 與 3 則幾乎相同。
f* = f - α ( f - g ) / 2 ,我們知道當嵌入量 α 為 0% 時, f 與 g 之間的差距為 ( f - g ), 當 α 越來越大時, f* 與 g* 會越來越接近, 當 α 達到 100% 時, 則
g* = g + α ( f - g ) / 2 .
f* = f - ( f - g ) / 2 = ( f + g ) / 2 ,換句話說, 當全部的冗餘位元都拿來做為嵌入機密訊息之用時, f* = g* = ( g + f ) / 2.
g* = g + ( f - g ) / 2 = ( g + f ) / 2 .
(1- α ) g ≥ α ( f - g) /2上述式子可以化簡得到 α 的預先估計值(a priori estimate), 做為嵌入機密訊息時的參考:
α ≤ 2 g / (f + g)給定一個機密訊息, 我們可以使用這個估計值來選擇一個用有足夠冗餘位元來保持原始 frequency counts 的掩護影像。有趣的是, 擁有更多 DCT 係數的影像, 並不代表擁有更多可供嵌入機密訊息的冗餘位元, Figure 6 說明了此一現象。Figure 6 中的每一個圈圈代表一個影像, 橫軸表示其擁有的 DCT 係數的總數, 總軸表示經過上述公式計算後, 所得到可以用來嵌入機密訊息的比例(fraction)。
1. For any part of the image, the distribution of the DCT coefficients should be similar to the unmodified image.仔細剖析這兩個需求, 要同時達到最佳狀況是不可能的。因為如果要讓第二個需求 - 校正個數達到最小, 就要先分析整體的嵌入狀況, 再著手校正所產生整體誤差, 在這種情況下, 很可能發生某些部分影像 DCT 係數的分布, 無法跟原始分布一樣。換句話說, 要做到任何部分影像的 DCT 係數分布和原始分布一樣, 就必須在這個部分影像中, 立即把嵌入機密訊息的走樣修正回來。如此, 就不可能使校正數目達到最小。作者針對這個問題, 提出一個妥協的方法, 為每個頻率(frequency) 定義了一個臨界值 (threshold), 來表示該 frequency count 可容忍的誤差值。
2. The number of corrections necessary to preserve statistical properties should be small.
標記 1 : 從原始掩護影像中, 計算 DCT 頻率的直方圖, 並將之存放於陣列 N 之中。Algorithm 1 針對每一個可供嵌入的位置, 從影像的開端開始處理, 如果找到一個 DCT 係數遭到修改, 他並不會直接就去想辦法校正回來, 而是看看這個修改是否已經超出可容忍的程度, 如果只是就先去看看與其配對的 DCT 係數 AdjDCT (標記 3) 是否也存在誤差值, 如果也存在誤差值 (標記 4), 那就正好可以抵銷, 不需另外做修正, 以滿足第二個需求 - 校正越少越好。如果 AdjDCT 並不存在誤差值, 再加上本身的誤差尚未超出容忍值 (標記 5), 則暫時先不做校正動作, 僅是累計其誤差值 increment Nerror [DCT(i)]。如果誤差已經超出容忍值 N*[DCT(i)] 了, 為了滿足第一項需求, 必須要立即執行校正程序: 在附近找到配對的係數修正回來, 也就是執行 Algorithm 2: exchDCT(i, DCT(i)); 如果找不到配對的係數, 則記錄其誤差, 留待最後階段再一起做大範圍 (從影像末端 k, 開始往前找) 的校正工作。
標記 2 : 決定每一個頻率可容忍的誤差值, 並將之存放於陣列 N* 之中。
計算方式如下:
k ← number of coefficients in image;
α← 0.03 * 5000 / k ;
N*(i) = α * N(i);
用陣列 N error 記錄每個 DCT 係數目前的累積誤差。
Nerror (i) ← 0;
標記 3 : AdjDCT ← DCT(i) ⊕ 1;
If the number of errors for the coefficient, Nerror[DCT(i)], can be incremented without exceeding its threshold value. If another increment is possible, we continue with the next modification. Otherwise, we have to correct the current modification in the image. The exchDCT algorithm is responsible for that.2. 最後階段, 進行大範圍的搜尋, 將所有的誤差都校正回來。雖然, 並不是所有的誤差都可以校正回來, 但只要能夠將大部分的誤差都校正回來, 就不會被偵測出來。
After all modifications have been examined, we need to correct all remaining errors. Not all the corrections might be possible. However, if we are able to correct most of the errors, changes in the histogram are not detectable.
Niels Provos, "Defending Against Statistical Steganalysis,"10th USENIX Security Symposium, August 13-17, 2001.
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Dear Yeuan-Kuen Lee,
We wish to congratulate you on the acceptance of your submission with paper ID: 154 as an oral presentation in the PSIVT2009 program. Review comments for your paper are now available in the papers management system: https://cmt.research.microsoft.com/PSIVT2009 .
The camera-ready paper deadline is on 17 October 2008, and paper preparation instructions can be found at http://psivt2009.nii.ac.jp/node/39 . Please note that for your paper to be published in this conference, the camera-ready paper must be received by the deadline, and one of the authors must register for the conference by this deadline as well.
We are looking forward to the presentation of your paper in PSIVT2009.
Best regards,
PSIVT2009 Program Committee
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Author: Toby SharpWhen a sample is visited, its data value is modified so that its least significant bit (LSB) is equal to the next bit of the secret data. The LSBs are not simply replaced; instead the whole sample value is incremented or decremented if the LSBs differ. This avoids the "pairs of values" statistical attack introduced in [9]. At each sample, one operation bit is taken from the generator and, if required, is used to determine whether to increment or decrement the sample value.很可惜地, 論文中提到的隱藏工具 Hide, 網路上已經找不到下載點了。A. Westfeld 在 IHW 2002 年所提出的論文 "Detecting Low Embedding Rates" 中有一張執行的初始畫面(Fig. 6),
