On Jan 24, 2013, at 8:13 PM, Dave Thompson <dthomp...@prinpay.com>
wrote:
> If you want to do it actually in Python:
> - get m and e from the public key (DER isn't hard to parse,
> you were already shown an example elsethread, and if Python
> doesn't have a direct way to convert bytestring to bignum
> which I'd expect it probably does you can just do some
> equivalent of x = 0; for i in 0..n-1 x = x*256+b[i]
> - do whichever padding you used with RSA_public_encrypt
> (this is probably the hardest part, especially if it's OAEP)
> - take the padded data as a bignum (ditto) and do pow(data,e,m)
> - take the result as a bytestring (perhaps implicitly)
I dug up the X,690 document that describes the DER format, and that is
basically the approach that I've been working on. I now have a very basic DER
parser that will handle the Sequence and Integer types that are in the public
keys that I'm dealing with. This gives me a Python long integer of 168 bits
for e and another 24-bit integer for m. I should be able to pass these to the
M2Crypto.RSA.new_pub_key() function once I can get them encoded correctly (they
need to be in the OpenSSL MPINT format).
Once I get that working I should then be able to use the other M2Crypto
routines to encrypt my data and my test system should be good to go. But it's
been a long week even with the holiday, so I'm going to leave that until
Monday. Thanks for all the pointers.
/dwight
Dwight Tovey
Laserjet R&D Engineer
dwight.to...@hp.com
(208)396-4645
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