Vulnerability Note VU#940388

GnuPG creates ElGamal keys for signing using insufficient entropy

Overview

Gnu Privacy Guard (GnuPG) is a cryptographic utility used to generate cryptographic keys and perform other cryptographic functions. A vulnerability in the way GnuPG generates ElGamal keys has been discovered. This vulnerability renders ElGamal signing key untrustworthy.

I. Description

A vulnerability in the algorithm to generate ElGamal sign+encrypt keys can permit an attacker to generate valid signatures without access to the private key. This vulnerability does not affect encrypt-only (type 16) ElGamal keys, only the ElGamal sign+encrypt key (type 20) when used to make a signature with a GnuPG version 1.0.2 or later.

II. Impact

A remote attacker can generate a valid signature without access to the private key.

III. Solution

Revoke your ElGamal signing keys. GnuPG has released a patch for version 1.2.3 or you can upgrade to version 1.2.4 or later.

Systems Affected

Vendor	Status	Date Notified	Date Updated
GNU Privacy Guard	Vulnerable	29-Dec-2003

References

http://www.secunia.com/advisories/10304/
http://www.securityfocus.com/bid/9115
http://www.secunia.com/advisories/10349/
http://www.secunia.com/advisories/10400/
http://www.secunia.com/advisories/10399/

Credit

Thanks to Werner Koch for his advisory on this issue, and Phong Nguyen for reporting this vulnerability.

This document was written by Jason A Rafail.

Other Information

Date Public:	2003-11-27
Date First Published:	2003-12-29
Date Last Updated:	2003-12-29
CERT Advisory:
CVE-ID(s):	CAN-2003-0971
NVD-ID(s):	CAN-2003-0971
US-CERT Technical Alerts:
Metric:	6.33
Document Revision:	7

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