Chosen-Ciphertext Attacks against PGP and GnuPG
Bei einem Chosen-Ciphertext Angriff versucht der Anreifer aus einem verschlüsselten Text, der an das Opfer von einem seiner Kommunikationspartner gesendet wurde (E-Mail) und den der Angreifer abgefangen hat, an den darin enthaltenen Klartext zu gelangen.
Dazu erstellt der Angreifer aus dem abgefangenen, verschlüsselten Text 1-2 neue Versionen, indem er Paket-, Feldinformationen verändert und zufällige Daten in das Paket "injiziert" und sendet diese an das Opfer. Wenn das Opfer die Nachrichten entschlüsselt, wird auf grund der Manipulationen durch den Angreifer ein verstümmelter Klartext ausgegeben.
Das Opfer sendet an den Angreifer eine Antwort, z. B. mit der Nachfrage, was eigentlich mitgeteilt werden sollte und *zitiert gleichzeitig den verstümmelten Klartext* (eine normale Funktion aller E-Mail Programme, die die meisten Anwender auch gebrauchen).
Aus den Daten des zurückgegebenen Textes kann der Angreifer nun den Klartext des ursprünglichen, verschlüsselten und von ihm abgefangenen Text ermitteln. Das Opfer wird deshalb bei diesem Angriff als "Entschlüsselungsorakel" bezeichnet.
Gegenmassnahmen>
Kompressionsroutinen sollten nicht deaktiviert werden
Die eventuell sich anschliessende Behandlung mit Komprimierprogramme beschränkt sich auf Zusammenfassungen mehrerer Dateien in einer zusätzlichen Versandhülle.
- A Chosen Ciphertext Attack against Several E-Mail Encryption Protocols
J. Katz and B. Schneier
9th USENIX Security Symposium, 2000 - Implementation of Chosen-Ciphertext Attacks against PGP and GnuPG
K. Jallad, J. Katz, and B. Schneier
Information Security Conference 2002 Proceedings, Springer-Verlag, 2002 - CNN.com/SCI-TECH:
Flaw discovered in encryption software
PGP hole could let unauthorized people decode e-mail
12. August 2002
ASCII Armor Parser Vulnerability
Release:
09.04.01
Name:
Windows PGP (Pretty Good Privacy) ASCII Armor Parser Vulnerability
Application:
PGP (Pretty good privacy) Version 5 to 7.0.3 (latest)
Platforms:
Windows 95, 98, Millennium, NT, Windows 2000, (see 'Vulnerable Versions'
section in the advisory)
Severity:
Opening an ASCII armored file such as a public key or a detached
signature can cause the creation of an arbitrary file on the target
machine. On the Windows platform this can lead to the execution
of arbitrary code on the target machine.
Author:
Chris Anley dec0de@atstake.com
PGP (Pretty Good Privacy) is a suite of encryption tools originally
published in 1991 by Phil Zimmermann to enhance personal privacy.
It has become the de facto standard for email encryption, winning
numerous industry awards and spawning a variety of alternative versions.
PGP Security, Inc. currently maintains the commercial version of
PGP also providing a version that is freely downloadable.
The PGP ASCII Armor parser provided with most versions of PGP (see 'Vulnerable Versions' section in the advisory) contains a behaviour that allows the creation of an arbitrary file in the same directory as the armored file. Since this file can contain arbitrary bytes, this can easily lead to the execution of arbitrary code on the Windows platform.
Full
Details
Proof-of-Concept
File
Vendor
Patch: PGP Desktop Security 7.0.4 Hotfix 1
Vendor
Patch: PGPfreeware 7.0.3 Hotfix 1
PGPsdk Key Validity Vulnerability
04.09.01
A vulnerability in PGP's display of key validity has been discovered that could allow an attacker to fool users into thinking that a valid signature was created by what is actually an invalid user ID. If the attacker can obtain a signature on their key from a trusted third party, they can then add a second user ID to their key which is unsigned. The attacker must then switch the unsigned false user ID to primary and convince the victim to place the key on their keyring. In such a case, some of the displays in PGP do not properly identify the false user ID as invalid because the second user ID is fully valid. Whenever PGP displays validity information on a per-user ID basis, the display is correct. Thus, attentive users who examine the user IDs of all public keys which they import to their keyrings will immediately notice this problem before it could have any impact.
This issue was discovered and reported to Network Associates/PGP Security, Inc. by Sieuwert van Otterloo.
This issue has been corrected such that all key validity displays in PGP will properly mark the unsigned user ID as invalid. Hotfixes are now available for the following products:
PGP Corporate Desktop v7.1 (MacOS9/Win32)
PGP Personal Security v7.0.3 (MacOS9/Win32)
PGP Freeware v7.0.3 (MacOS9/Win32)
PGP E-Business Server v7.1 (Linux/Solaris/AIX/HPUX/Win32)
Product upgrades are available for the following products:
PGP E-Business Server v6.5.8x (OS/390)
PGP E-Business Server v7.0.4 (Linux/Solaris/AIX/HPUX/Win32)
The hotfixes and upgrades can be found at:
http://www.pgp.com/naicommon/download/upgrade/upgrades-patch.asp
The diffs for patching the source release of PGP version 6.5.8 (including the PGPsdk version 1.7.8) can be found here
Network Associates/PGP Security Inc. has published the PGPsdk source
code in electronic form for academic and cryptographic peer review.
The source packages can be downloaded from:
http://www.pgp.com/downloads/default.asp
CKT PGP
gepatcht gegen:
- ADK-GAU
- ASCII Armor Parser
- Key Validity Vulnerabilities
GnuPG
gepatcht gegen:
- ADK-GAU - nicht betroffen
- Klima-Rosa
- ASCII Armor Parser - nicht betroffen
- Key Validity Vulnerabilities