On Thu, Mar 17, 2016, Viktor Dukhovni wrote:
>
> > On Mar 17, 2016, at 6:32 PM, Blumenthal, Uri - 0553 - MITLL
> > <u...@ll.mit.edu> wrote:
> >
> > Oh, and I'd much prefer to stay at the EVP level, rather than invoke BIO
> > primitives for this task.
>
> Well you can work with
> http://openssl.org/docs/manmaster/crypto/EC_KEY_key2buf.html
> to extract EC public key octets.
That's only available in the master branch, only encodes the key value and not
its parameters and of course it only works for EC.
> If you want an ASN.1 encoded "SPKI" object (i.e. an
> X509_PUBKEY in OpenSSL) then you can use
>
> X509_PUBKEY *pk = NULL;
> unsigned char *buf = NULL;
> EVP_PKEY *key;
>
> key = ... ; /* Get a keypair */
>
> if (X509_PUBKEY_set(&pk, key) <= 0) {
> /* error */
> }
>
> len = i2d_X509_PUBKEY(pk, &buf);
> if (len < 0 || buf == NULL) {
> /* error */
> }
>
> /* buf contains ASN.1-encoded SPKI, use it */
>
> OPENSSL_free(buf);
> X509_PUBKEY_free(pk);
> EVP_PKEY_free(key); /* If no longer needed */
>
> A shorter version of the above is possible via i2d_PUBKEY() which
> handles the creation, encoding and destruction of the intermediate
> X509_PUBKEY:
>
> int i2d_PUBKEY(EVP_PKEY *a, unsigned char **pp)
> {
> X509_PUBKEY *xpk = NULL;
> int ret;
> if (!a)
> return 0;
> if (!X509_PUBKEY_set(&xpk, a))
> return 0;
> ret = i2d_X509_PUBKEY(xpk, pp);
> X509_PUBKEY_free(xpk);
> return ret;
> }
>
>
That's the preferred route as it uses the standard SubjectPublicKeyInfo
format and works with any supported public key type.
Steve.
--
Dr Stephen N. Henson. OpenSSL project core developer.
Commercial tech support now available see: http://www.openssl.org
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