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.

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.

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Impact

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

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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.

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Vendor Information

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GNU Privacy Guard __ Affected

Updated: December 29, 2003

Status

Affected

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

Please see the GnuPG advisory at <http://lists.gnupg.org/pipermail/gnupg-announce/2003q4/000276.html&gt;

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%23940388 Feedback>).

CVSS Metrics

Group	Score	Vector
Base
Temporal
Environmental

References

• <http://www.secunia.com/advisories/10304/&gt;
• <http://www.securityfocus.com/bid/9115&gt;
• <http://www.secunia.com/advisories/10349/&gt;
• <http://www.secunia.com/advisories/10400/&gt;
• <http://www.secunia.com/advisories/10399/&gt;

Acknowledgements

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

CVE IDs:	CVE-2003-0971
Severity Metric:	6.33 Date Public: