Title: OpenPGP Private Key Attack Vulnerability
Severity: LOW
Description:
The OpenPGP Message Format Standard provides information on the message-exchange packet formats used by OpenPGP to provide encryption, decryption, signing, and key management functions. Many of the techniques described in the standard have been adopted into widely-used public key encryption programs.
Two cryptologists, Vlastimil Klima and Tomas Rosa, have found a flaw in the OpenPGP key format which could make it possible for an adversary to forge a PGP signature using a victim's private key without knowing the pass phrase for that key.
The flaw is the result of a design error; programs based on the OpenPGP format do not perform any integrity checks that might recognize certain modifications to private keys. The attack works against keys created with an asymmetrical algorithm which gains its security from the difficulty of the discrete logarithm problem, such as DSA and RSA. It is noteworthy that the implementation of RSA in the commercial version of PGP has been shown not to be vulnerable because of additional protections beyond OpenPGP format. This may also be the case for other implementations of PGP.
To successfully attack the flaw, an adversary must obtain a user's private key, make some minor modifications to it, and capture a message from the user signed using the modified key. Based on the captured message, the user's private key can be decrypted.
The practical impact of the attack is dependent on how the private key is obtained and modified. In many cases, if an adversary has the level of access required to make such modifications, considerably worse attacks are possible.
Affected Products:
- GNU GNU Privacy Guard 1.0.0
- GNU GNU Privacy Guard 1.0.1
- GNU GNU Privacy Guard 1.0.2
- GNU GNU Privacy Guard 1.0.3
- GNU GNU Privacy Guard 1.0.3b
- GNU GNU Privacy Guard 1.0.4
- Network Associates PGP 5.0.0
- Network Associates PGP 5.5.5
- Network Associates PGP 6.0.2
- Network Associates PGP 6.5.3
- Network Associates PGP 6.5.8
- Network Associates PGP 7.0.3
References:
- ICZ: Attack on Private Signature Keys of the OpenPGP format
- ICZ: OpenPGP Attack Press Release (in English)
- Internet Engineering Task Force: RFC 2440: OpenPGP Message Format
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