Hi all,
Did anyone have any luck with this one?
Thanks,
Pratyush Parimal.
---------- Forwarded message ----------
From: pratyush parimal <pratyush.pari...@gmail.com>
Date: Wed, Jun 25, 2014 at 10:43 AM
Subject: Converting public part of 'EVP_PKEY' structure to 'unsigned char*'
, and back.
To: openssl-users@openssl.org
Hi all,
I was trying to use ECDH (in OpenSSL v1.0.1f) for a project, and after
generating the EVP_PKEY structure, I needed to extract its public key and
send it over to the other party. I was unable to find a straightforward way
which worked for me.
What I tried was this:
EVP_PKEY*
extract_peerkey_3(EVP_PKEY* EVP_PKEY_both) //'both' meaning it contains
public + private
{
int len = 0;
len = i2d_PUBKEY(EVP_PKEY_both, NULL); //find out required buffer length
unsigned char *buf, *p;
buf = (unsigned char*) malloc(len); //allocate
p = buf;
len = i2d_PUBKEY(EVP_PKEY_both, &p);
const unsigned char* p2 = buf;
EVP_PKEY* EVP_PKEY_public = d2i_PUBKEY(NULL, &p2, len);
if (EVP_PKEY_public == NULL)
{
handleCryptoError("d2i failed", ERR_get_error());
}
return EVP_PKEY_public;
}
The function doesn't throw an error, but when I pass the returned
'EVP_PKEY_public' structure to the function 'EVP_PKEY_derive_set_peer', I
get an error message "error:10071065:elliptic curve
routines:EC_POINT_cmp:incompatible objects".
I also tried to follow the steps given at
http://stackoverflow.com/questions/18155559/how-does-one-access-the-raw-ecdh-public-key-private-key-and-params-inside-opens
.
When i reconstruct the EVP_PKEY using the steps EC_POINT_oct2point()
-> EC_KEY_set_public_key()
-> EVP_PKEY_set1_EC_KEY(), the resulting EVP_PKEY does work for me. In fact
I'm able to derive the same secret on both sides using this sequence, but I
feel it's too roundabout.
I also saw the following:
http://marc.info/?l=openssl-users&m=116474297608094&w=2, which talks about
using 'i2d_PUBKEY', but I haven't been able to make it work so far.
Is my usage of d2i_PUBKEY or i2d_PUBKEY wrong in some way? Does anyone know
how to use them properly?
Any help will be appreciated.
Thanks!
Pratyush Parimal
