About "Czech attack"



(1)        Press conference

(2)        Photogalery

(3)        The New York Times, March 21, 2001

(4)        The New York Times, March 23, 2001

(5)        Czech television about it

(6)        Bruce Schneier about Czech attack

(7)        Dorothy Denning about Czech attack

(8)        Further reports



(1)           Press conference

20. 3. 2001, Press conference, ICZ, March 20, 2001, Prague, press release: http://www.i.cz/en/onas/tisk4.html


ICZ Press Release, March 20th, 2001


Czech company ICZ cryptologists detected serious
security vulnerability of an international magnitude


Prague, March 20th, 2001 - A bug in worldwide used OpenPGP format has been found. The bug can lead to discovery of user’s private keys used in digital signature systems. OpenPGP format is widely used in many worldwide spread applications, including massively used programs like PGP(TM), GNU Privacy Guard, and others. The bug detection comes on the right time, as Philip Zimmermann, the creator of PGP program, has left Network Associates, Inc. and aims to boost OpenPGP format in other products for privacy security on Internet. From the scientific point of view, the discovery goes far beyond actual programs - it has wider theoretical and practical impact.


Decros (a member company of ICZ group) cryptologists Vlastimil Klima and Tomas Rosa detected insufficient security protection of private signature keys while working on a research for the National Security Authority. The private signature key is the most sensitive and therefore the most classified information in all digital signature systems. The attack is described in detail in a large research report. The report is to be released on Internet (http://www.i.cz) in both Czech and English shortly.


The attack on OpenPGP format leading to discovery of DSA and RSA private signature keys is described in the research report. OpenPGP format is being proposed as an Internet standard for exact definition of content and meaning of data records, in relation to encryption and to digital signature.


This format is used not only in PGPTM programs group, but also in other applications, including GNU Privacy Guard. The list of products based on OpenPGP is available on Internet at http://www.pgpi.org/products. OpenPGP format and all the applications need to be reviewed the same way as PGPTM program itself.


The attack was successfully verified and demonstrated on PGPTM version 7.0.3 using AES and DH/DSS algorithms, which are deservedly being considered as highly secure.


The serious bug is caused by wrong implementation of the above-mentioned strongest cryptographic techniques. The private signature key is the basic and the most sensitive information in the whole system. The user is using it for digital signature. In all systems, including OpenPGP, it is therefore protected by a strong cipher. AES, one of the latest strong algorithms, has been used in the attacked system. However, the protection appears to be illusory.


The authors proved that attackers do not need to attack the strong cipher itself. They can simply bypass it as well as the secret user’s passphrase. A slight modification of the private key file followed by capturing a signed message is enough. These tasks can be performed without knowledge of the user’s passphrase. After that, a special program can be run on any office PC. Based on the captured message, the program is able to calculate the user’s private key in half a second. The attacker can then sign any messages instead of the attacked user. Despite of very quick calculation, the program is based on a special cryptographic know-how.


Insufficient security of public and private parts of signature keys in OpenPGP format has been analyzed for DSA and RSA algorithms. The step-by-step description of the attack on both private signature keys is being demonstrated. The attacks apply to all RSA and DSA parameter lengths (modules, keys).


The demonstrated attacks have a strong impact on security of the programs mentioned above. To complete the attack, it is not always necessary to visit the attacked user’s workstation. The vulnerability of the system is also in the files with exported private keys used by the user for transferring the keys between workstations. The fact that the private key is stored in an encrypted form can cause an illusory security feeling. If this file or diskette is captured by an attacker during the transfer, the security of user’s private key is in serious danger.


We can often see that users store private key files on shared devices on a network to maintain easy access. Knowing that the key is protected by a strong cipher, the user considers such a storage to be safe enough. The authors proved that this feeling is illusory. Typically, the server administrator can be the attacker.


Knowing the details of the demonstrated attack, the user of programs based on OpenPGP is in a difficult situation when he/she realizes that an invalid signature value has been generated. The user cannot be sure whether this happened because of the attack, or ‘just’ because of a technical failure. It is obvious that every file with an invalid signature has to be handled carefully, the same way as a file with the private key in open form! This includes careful secure wiping of the file from the workstation or the server.


The completed analysis of the OpenPGP format has found serious defects that make OpenPGP based applications vulnerable. The practical example is PGPTM program which is not resistant to the attack on DSA algorithm. However, the program is resistant to the attack on RSA algorithm because of additional protections beyond OpenPGP format.


Though the attack relates to RSA and DSA algorithms in OpenPGP, similar vulnerabilities can be expected in other asymmetrical cryptographic systems, including systems based on elliptic curves. OpenPGP format and PGPTM program are likely not the only examples of systems that can be attacked because of insufficient protection of the parameters mentioned above. In the end of their research report, the authors propose cryptographic measures correcting OpenPGP format and PGPTM program as well. They strongly appeal for very careful design of cryptographic systems.

(2)           Photogalery

Photogalery here.


(3)           The New York Times, March 21, 2001

Cryptologists Discover Flaw in E-Mail Security Program


Two cryptologists announced yesterday that they had found a flaw in the most widely used program for sending encrypted, or coded, e-mail messages. If confirmed, the flaw would allow a determined adversary to obtain secret codes used by senders of encrypted e-mail.

The program, called P.G.P. for Pretty Good Privacy, is used by human rights organizations to protect vulnerable sources, by corporations to ensure secure communications and by millions of individual users. American security experts cautioned that they could not fully judge the accuracy of the claim, which was issued in Prague, before more technical details become available. The experts also noted that some sort of access to the sender's computer — either directly or via the Internet — would be needed to exploit any such flaw.

According to a statement issued yesterday by ICZ, an information technology company in Prague with about 500 employees, the cryptologists, Vlastimil Klima and Tomas Rosa, found the problem while doing research on secure communications for the Czech government.

"It is very serious," said Kriz Zdenek, general manager of ICZ, adding that a technical paper on the finding would be made available by Friday on the company's Web site (www.icz.cz/).

Mark McArdle, vice president of P.G.P. engineering at Network Associates in Santa Clara, Calif., which licenses the encryption program to corporate and individual users, said he had already assigned a team of engineers to check out the claim, which he learned of yesterday from a journalist.

"We are very eager to both analyze this and respond to it," Mr. McArdle said. "We want to make sure that our systems are completely robust."

He expressed surprise that the Czech company did not inform him of the problem so that a software fix, often called a patch, could be made available with the announcement of any bug. But Miroslav Votruba, marketing director at ICZ, said several e- mail messages informing Network Associates of the problem more than a week ago received no response.

"We are willing to cooperate before the algorithm or description of the problem will be released on the Web," Mr. Votruba said.

P.G.P. relies on a type of cryptography that uses two separate keys, one to encode a message and one to decode it. The flaw claimed by the cryptographers does not involve cracking the code itself, which is considered virtually invulnerable, but would work around it by allowing an intruder to steal one of the keys held privately by a user.

Without such a flaw or bug, the private key would be unavailable even to an intruder who gained access to a computer, because it exists there only in scrambled form. The ICZ announcement says there is a way to unscramble it but gives few details. Mr. McArdle said such a bug would mainly affect the coded electronic "signatures" that allow the recipient to verify the sender's identity. In effect, it would allow the intruder to impersonate the sender in future communications.

"This is probably real," said Bruce Schneier, founder and chief technology officer of Counterpane Internet Security in San Jose, Calif., referring to the bug. But he said it showed that e-mail security involved more than simply protecting the message in transit on the Internet.

Dr. Michael A. Caloyannides, a senior fellow at Mitretek Systems in McLean, Va., said the bug would be "a bit of a shock," since P.G.P. had been considered essentially invulnerable. And Matthew Zimmerman, project coordinator for the Science and Human Rights Program of the American Association for the Advancement of Science, confirmed that his organization routinely used P.G.P. to protect dissidents and informers around the world.

But even if the problem does turn out to be serious, said Jonathan Zuck, president of the Association for Competitive Technology in Washington, an industry group involving information technology, security-conscious Internet users should not panic.

"This kind of technology arms race is always a factor in any new technology standard," Mr. Zuck said, adding that the eventual result should be an improved encryption program.

(4)           The New York Times, March 23, 2001

Experts Differ on How Flaw Will Affect Coded E-Mail


Security experts have confirmed that the most widely used program for sending encrypted e-mail messages has an obscure vulnerability that could allow a determined intruder to obtain secret codes, as two Czech cryptologists announced on Tuesday.

But some experts differ sharply with the cryptologists on the practical importance of the vulnerability, which is now believed to have existed in the program since it was invented a decade ago. The program — called P.G.P., for Pretty Good Privacy — is used by millions of people around the world.

The cryptologists, Dr. Vlastimil Klima and Tomas Rosa of ICZ, an information technology company in Prague, said the flaw could allow an intruder to forge the "digital signature" that senders of encrypted e- mail use to identify themselves in secret communications or financial transactions.

Mark McArdle, vice president for P.G.P. engineering at Network Associates in Santa Clara, Calif., which licenses the program to corporate, organizational and individual users, agreed that Dr. Klima and Mr. Rosa were correct. But Mr. McArdle said their technique was impractical, since it required access to digital files that should exist only on the sender's computer or on a secure floppy disk.

The cryptologists strongly disagree, saying the files are often floating about in shared computer networks or in computers with open links to the Internet.

Everyone seems to agree that the episode reveals how elusive privacy has become in the age of electronic communication, when only multiple precautions designed by security professionals have a chance — and even then sometimes fall short.

"It is a very practical attack," Dr. Klima said of the method he and Mr. Rosa developed. Since workers on computer networks often wish to use P.G.P. at multiple workstations, a scrambled form of their signature code — which they can unscramble using a phrase known only to them — may exist in a central repository accessible to system administrators and others. Only the file containing the scrambled code is required for the attack, Dr. Klima said.

But Mr. McArdle said his company specifically recommended that the file be kept in a secure location and not on a network. He said exceptions to this practice were so rare that his company might not even offer software to patch the vulnerability until a new version of P.G.P. becomes available, perhaps next summer.

Philip Zimmermann, P.G.P.'s inventor, who is no longer affiliated with Network Associates, refused even to call the discovery a flaw, saying it was merely an interesting "mathematical observation," since any hacker who gained access to a secure computer — where the codes should be kept — could do far more damage than simply forge e-mail messages. For example, in 1999 federal agents planted a so-called sniffer in the keyboard of an organized- crime suspect to obtain all his passwords.

Because encrypted digital signatures gained legal standing last year, however, in a bill signed by President Bill Clinton, the P.G.P. vulnerability has caught the attention of the online security community.

Some security experts said the episode illustrated that as a practical matter, ordinary users of the Internet had little hope of maintaining privacy in the face of a sophisticated adversary.

"The reality of life is that, in fact, the majority of people do not diligently guard their keys," said Dr. Michael A. Caloyannides, a senior fellow at Mitretek Systems in McLean, Va. Against a determined intruder, he said, "it's kind of like locking the front door and leaving the back door wide open."


(5)           Czech television about it

28. 3. 2001, ČESKÁ TELEVIZE, news "Tady a teď", record (RealPlayer, 3.7MB), photogalery.


(6)           Bruce Schneier about Czech attack

"A vulnerability was found in the OpenPGP standard. If an attacker can modify the victim's encrypted private key file, he can intercept a signed message and then figure out the victim's signing key. This is a problem with the data format, and not with the cryptographic algorithms. I don't think it's a major problem, since someone who can access the victim's hard drive is more likely to simply install a keyboard sniffer. But it is a flaw, and shows how hard it is to get everything right. Excellent cryptanalysis work here."


Bruce Schneier
CTO, Counterpane Internet Security

(7)           Dorothy Denning about Czech attack

"Your report on the vulnerabilities of PGP signatures is most interesting. Congratulations on your fine work."


Prof. Dorothy E. Denning
Georgetown University


(8)           Further reports

Further articles, reports and information about it were in all main Czech media (television, radio, newspapers, magazines), in many foreign media and in a lot of internet sources (ZDNet, CNET, ACM, CNN, TheRegister and others).