On 15 May 2012 15:22, Fábio Resner <fabiu...@gmail.com> wrote:
> Hi,
>
> I'm trying to write an app to generate public/private/shared key for ECDH.
> Here is what I was able to build based on examples:
>
> #include <openssl/ssl.h>
>
> #define ECDH_SIZE 67
>
> int main() {
> EC_KEY *ecdh = EC_KEY_new();
> const EC_POINT *point = NULL;
>
> EC_POINT *point2;
> const EC_GROUP *group;
>
> // const void *pubkey = NULL;
> unsigned char *pubkey = NULL;
> void *shared = NULL;
>
> //Generate Public
> ecdh = EC_KEY_new_by_curve_name(NID_secp521r1);
> EC_KEY_generate_key(ecdh);
>
> point = EC_KEY_get0_public_key(ecdh);
> EC_POINT_point2oct(EC_KEY_get0_group(ecdh), point,
> POINT_CONVERSION_COMPRESSED, pubkey, ECDH_SIZE, NULL);
>
I am not familiar with the ECDH functions....but I am familiar with
the EC functions and this line does not look right.
If you pass a null pointer for a buffer to point2oct then the function
will return the size of the buffer that you require. You need to check
the return value, malloc a buffer of the required size and then
re-call point2oct.
> //ComputeKey
> group = EC_KEY_get0_group((ecdh));
> point2 = EC_POINT_new(group);
>
> EC_POINT_oct2point(group, point2, pubkey, ECDH_SIZE, NULL);
>
> ECDH_compute_key(shared, ECDH_SIZE, point2, ecdh, NULL);
As I said I'm not familiar with the ECDH functions...but this looks
like you are trying to generate a shared key using only one
public/private key pair??
> EC_POINT_free(point2);
> EC_KEY_free(ecdh);
> ecdh = NULL;
>
> printf("To the end");
>
> return 0;
> }
>
> But it just broke on EC_POINT_oct2point(group, point2, pubkey, ECDH_SIZE,
> NULL);
> And pubkey is exiting EC_POINT_point2oct(EC_KEY_get0_group(ecdh), point,
> POINT_CONVERSION_COMPRESSED, pubkey, ECDH_SIZE, NULL); with a NULL value.
> The program exists and gives no segFAULT or any erros messages.
>
> Any suggestions?
>
> Thanks,
>
> --
> Fabio Resner.
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