> From: owner-openssl-us...@openssl.org On Behalf Of Tovey, Dwight (LaserJet R&D FW Eng.) > Sent: Thursday, 24 January, 2013 10:55
> On Jan 23, 2013, at 3:56 PM, Dave Thompson <dthomp...@prinpay.com> > wrote: > > > Most utilities, yes, although the library supports both. > > (The routines named RSAPublicKey do the specific PKCS#1 form, > > the routines named RSA_PUBKEY or just PUBKEY do the wrapped form.) <snip> > > Getting back to the original question, according to Wikipedia > > Python has builtin modular exponentiation on bignums as pow(x,e,m), > > so probably all OP needs is extract the modulus and (public) exponent > > from the key, pad and convert the data and do that. > > With the help of the comments here I have made some progress. > For a proof-of-concept, I wrote a little C program that > passed the binary public key through the OpenSSL library > function d2i_RSAPublicKey() to get a RSA structure. I could > then use this in a call to RSA_public_encrypt() to encrypt > the plaintext data to send back to the device, and the device > successfully accepted it. So now I want to translate that C > program into python. > > Dave - you mention using the pow() function in python to > extract the modulus and exponent. Could you elaborate on > that? Or did you mean that once I have the modulus and > exponent that I could use pow() in the encryption process? > It's been several years since I last looked at encryption > programming, so please excuse my lack of understanding. > The latter. The significant content of the public key is two integers, the modulus m which is large and the public exponent e which is usually and here small. Given those two integers, raw RSA encryption is the bignum computation x ^ e mod m, which apparently Python builtin pow() can do. I don't use Python myself; I'm going by the doc I found. > I can use the M2Crypto python module (python wrapper for > OpenSSL) in our environment to do the encryption, but so far > I haven't been able to figure out how to get it to accept the > public key. I may have to spend the weekend with my nose > buried in an encryption primer. > Elsethread you confirm that giving the module the "wrapped" publickey worked. If you're happy using the module that's probably easiest -- OpenSSL already has the code. 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) ______________________________________________________________________ OpenSSL Project http://www.openssl.org User Support Mailing List openssl-users@openssl.org Automated List Manager majord...@openssl.org
