The OpenPGP PGP standard allows an attacker to determine the private signature key via a cryptanalytic attack in which the attacker alters the encrypted private key file and captures a single message signed with the signature key.
ftp://ftp.caldera.com/pub/security/OpenLinux/CSSA-2001-017.0.txt
archives.neohapsis.com/archives/bugtraq/2001-03/0252.html
archives.neohapsis.com/archives/bugtraq/2001-03/0274.html
archives.neohapsis.com/archives/bugtraq/2001-03/0311.html
www.osvdb.org/11966
www.redhat.com/support/errata/RHSA-2001-063.html
www.securityfocus.com/bid/2673
exchange.xforce.ibmcloud.com/vulnerabilities/6558