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GnuPG ElGamal Signing Weakness Expose Private Key
Secunia Advisory: SA10304
Release Date: 2003-11-27
Last Update: 2003-12-29
Popularity: 10,997 views

Critical:
Moderately critical
Impact: Spoofing
Exposure of sensitive information
Where: From remote
Solution Status: Vendor Patch

Software:GnuPG / gpg 1.0.x
GnuPG / gpg 1.2.x

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CVE reference:CVE-2003-0971


Description:
A weakness has been identified in the handling of ElGamal keys in GnuPG, which exposes the private key.

The problem is a that certain versions of GnuPG creates ElGamal sign+encrypt keys (type 20) in a cryptographically weak way. This can be exploited to derive the private key.

In an advisory from the developers of GnuPG, it is stated that all ElGamal type 20 keys should be considered compromised.

This affects ElGamal type 20 keys generated with GnuPG 1.0.2 to 1.2.3.

ElGamal encrypt-only keys (type 16) are not affected.

Further details are available in the original advisory.

Solution:
Future versions of GnuPG will not include support for ElGamal type 20 keys.

Patch for GnuPG 1.2.3, which will remove the support for ElGamal type 20 keys:
http://lists.gnupg.org/pipermail/gnupg-users/2003-November/020771.html

Provided and/or discovered by:
Phong Nguyen

Changelog:
2003-12-04: Added CVE reference.
2003-12-29: Added link to CERT.

Original Advisory:
http://lists.gnupg.org/pipermail/gnupg-users/2003-November/020772.html

Other References:
CERT VU#940388:
http://www.kb.cert.org/vuls/id/940388


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