[cryptography] Duplicate primes in lots of RSA moduli

Werner Koch wk at gnupg.org
Thu Feb 16 04:15:12 EST 2012

On Wed, 15 Feb 2012 23:22, fw at deneb.enyo.de said:

> implementations seem to interpret it as a hard limit.  The V4 key
> format has something which the OpenPGP specification calls an
> "expiration date", but its not really enforceable because it can be
> stripped by an attacker and extended by someone who has access to the
> private key, by creating a new self-signature.  In this sense, the

The first part of your claim is wrong.  The expiration date can't be
stripped by an attacker because it is bound by a self-signature to the
key.  The self-signature is mandatory for OpenPGP keys.  In that sense
it is the same as with the NotAfter date in X.509.

Sure, if you have access to the primary private key [1] you can mount
almost all kinds of attack.  I know that you consider it a weakness that
the expiration date is not included in the fingerprint.  However, we
considered it an advantage to allow the owner of the private key to
prolong the expiration date.



[1] There is no need to keep the primary private key online.  For day to
    day operations it is possible to use secondary keys.

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