Generate an insecure public / private key pair I am looking for a way to generate an "insecure" public key pair. and by insecure I actually mean a pair that is breakable using brute-force (or other encryption) methods.

As far as I know PGP started with 128bit-keys. and at this point I can only find tools to generate keys using 1024bit or more.

Is there a way to generate a key pair with lets say 56bit (or even less) that will still generate a valid Certificate than can be used in PGP messages?
I am not sure to fully understand your question, but what you can do is the following: take $r=2^{512}$, and compute $p=r+\delta$ and $q=r-\delta^\prime$ such that $p$ and $q$ are prime numbers, and $0\leq \delta, \delta^\prime &lt; 2^{32}$. Then you have an RSA key at you disposal that can be broken by a brute force search on $\delta$, which should take strictly less than $2^{32}$ trials.