[pycrypto] How can I read a standard openssl private key with PyCrypto and decrypt with it?

William Heath wgheath at gmail.com
Wed Aug 19 11:06:26 CST 2009

I am looking for any way to do this on google app engine using any python
library.  Do you have any ideas on that?

On Tue, Aug 18, 2009 at 8:26 PM, Dwayne C. Litzenberger <dlitz at dlitz.net>wrote:

> On Tue, Aug 18, 2009 at 06:07:53PM -0700, William Heath wrote:
> >I generated a private key with:
> >
> >   openssl.exe req -x509 -nodes -days 365 -newkey rsa:1024 -keyout
> >sdgidfedapp11.corp.intuit.net.key -out sdgidfedapp11.corp.intuit.net.crt
> >
> >I can't figure out is how to use PyCrypto.RSA.construct with it
> >to decrypt something.
> [snip]
> >I am sure there is a way to do this with PyCrypto, anyone know how to do
> it?
> I am not aware of any simple way to do what you ask without using a
> separate library.  PKCS#1 and X.509 are not implemented in PyCrypto, and as
> far as I understand, you would need both to do anything useful with such a
> key.
> At this time, PyCrypto's API for RSA is somewhat confusing: It only
> implements textbook RSA, so it's not really useful for anyone except other
> crypto library developers (e.g. Paramiko, Twisted, etc.).  You might be
> able to use OpenSSL to generate hex values for each of the parameters, then
> parse the results and feed them to RSA.construct yourself using something
> like this:
>     openssl rsa -text -in sdgidfedapp11.corp.intuit.net.key
> However, since PyCrypto lacks PKCS#1 support, if you aren't careful or if
> you don't know exactly what you are doing, you will probably expose your
> private key to compromise.
> If you want to do practical public-key work with X.509 today, you might
> want to check out other libraries like pycryptopp, Google Key Czar, and
> M2Crypto.  Also, Paramiko (which depends on PyCrypto) might support at
> least reading those files, since IIRC they're also used for SSH private
> keys.
> Please do remember that PyCrypto's current RSA functions are insecure if
> used directly.  I would like to introduce a simple public key API at some
> point, but right now it doesn't exist.
> If you're doing any low-level work with RSA, you should at minimum, read
> and understand this overview paper:
>     http://www.cs.bgu.ac.il/~beimel/Courses/crypto/Boneh.pdf
> Also, as a side note, 1024-bit RSA keys are a little on the short side
> today.  I would recommend nothing less than 2048 bits:
>     http://www.google.com/search?q=1024-bit+RSA
> Hope that helps.
> Cheers,
> - Dwayne
> --
> Dwayne C. Litzenberger <dlitz at dlitz.net>
>  Key-signing key   - 19E1 1FE8 B3CF F273 ED17  4A24 928C EC13 39C2 5CF7
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