GnuPG’s ElGamal signing keys compromised
Friday, November 28th, 2003[Full-Disclosure] GnuPG’s ElGamal signing keys compromised:
In January 2000, as part of version 1.0.2, the GnuPG code was changed to create ElGamal keys which work more efficiently for encryption (selecting a smaller x secret exponent and using a smaller k for encryption). While making this change the problem with signing keys was accidentally introduced: the same small k for encryption was also used for signing. This can be used for a cryptographic attack to reveal the private key (i.e. the secret exponent x) if a signature made using that key is available. Such a signature is always available for primary ElGamal keys because signatures created with that key are used to bind the user ID and other material to the primary key (self-signatures). Even if the key was never used for signing documents it should be considered compromised.
