[PYTHON-CRYPTO] RSA exponent

[Dan Berger]

It's likely because OpenSSL (and the M2 wrapper) are returning an MPI -
which has it's length as the first four bytes and remainder being the
number in big-endian byte order.

On Tue, 2004-08-03 at 21:39 +0200, Larry Bugbee wrote:
> I could use some help...
> 
> When I generate a RSA key pair I use 65537 as the exponent.  Later when I go
> to extract the exponent I get 50397185.  In hex it's actually 00 00 00 03 01
> 00 01, but if I discard the 4 high order bytes, 01 00 01 evaluates to 65537.
>  Perhaps you have a suggestion?
> 
> Here is a minimalist version of my code.
> 
> from M2Crypto import RSA
> key = RSA.gen_key(1024, 65537)
> print type(key.e)
> print len(key.e)
> for c in key.e:
>     print ord(c),
> print
> e = 0
> for c in key.e:
> # e = (e << 8) + ord(c)
>  e = (e*256) + ord(c)
> print e
> 
> I get the same results on both MacOSX and Win2000.
>  - OSX 10.3.4, python 2.3, openssl 0.9.7b, M2Crypto 0.13 (with DSA patches)
>  - Win2000, python 2.3.4, openssl 0.9.7b, M2Crypto 0.13 (no patches)
> 
> OpenSSL is not the latest version, but I should be OK.
> 
> Thanks,
> 
> Larry
--

...Dan Berger [dberger at cs.ucr.edu]
   Department of Computer Science
   Surge Building, Room 357
   University of California, Riverside
   http://www.cs.ucr.edu/~dberger

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