[openssl-users] EVP_PKEY_set1_EC_KEY seems to not set something that EVP_PKEY_derive needs

[Ethan Rahn]

Wow,

That was quite the oversight of mine. That fixed the issue. Thanks so much,
I appreciate your patience in dealing with my confusion over the APIs!

Cheers,

Ethan

On Sat, Mar 11, 2017 at 12:28 PM, Matt Caswell <matt at openssl.org> wrote:

>
>
> On 11/03/17 18:38, Ethan Rahn wrote:
> >    size_t sharedSecretLen = 0;
>
> Set this to sizeof(sharedSecret).
>
> >
> >    // Now derive the Shared Secret
> >    EVP_PKEY_CTX *ctx;
> >
> >    ctx = EVP_PKEY_CTX_new(pkey, NULL);
> >    if (!ctx){
> >       fprintf( stderr, "Failed to make EVP_PKEY ctx\n" );
> >       ERR_load_crypto_strings();
>
> This should be called once at the start of your program - *before* any
> calls that might generate an error.
>
> >    if (EVP_PKEY_derive(ctx, sharedSecret, &sharedSecretLen) <= 0){
>
> From the EVP_PKEY_derive documentation:
>
> https://www.openssl.org/docs/man1.0.2/crypto/EVP_PKEY_derive.html
>
> "If key is not NULL then before the call the keylen parameter should
> contain the length of the key buffer, if the call is successful the
> shared secret is written to key and the amount of data written to keylen."
>
> Matt
>
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