OpenSSL 1.1 support status : what next?

[Douglas E Engert]

On 6/24/2017 11:35 AM, Emmanuel Deloget wrote:
> Hello Douglas,
> 
> On Fri, Jun 23, 2017 at 9:16 PM, Douglas E Engert <deengert at gmail.com <mailto:deengert at gmail.com>> wrote:
>  > OpenSC has taken a different approach to OpenSSL-1.1. Rather then writing
>  > a shim for OpenSSL-1.1, the OpenSC code has been converted to
>  > the OpenSSL-1.1 API and a sc-ossl-compat.h" file consisting of defines and
>  > macros was written to support older versions of OpenSSL and Libressl.
>  >
>  > https://github.com/OpenSC/OpenSC/blob/master/src/libopensc/sc-ossl-compat.h
>  >
>  > The nice part of this approach is when using OpenSSL-1.1 sc-ossl-compat.h
>  > does not do anything. It sole purpose to provide calls to the older APIs
>  > that are not going to change and eventually the sc-ossl-compat.h could be
>  > removed.
>  >
>  > Only the OpenSSL routines used by OpenSC have added to sc-ossl-compat.h
>  > but others defines and macro could be added.There are a few utilities that
>  > use still use a few #ifdef's during initialization.
> 
> This might be because I'm kind of a failure when I try to speak English but this is what I assumed to be a shim :) Of course, I might be wrong again :)

Yes it is a shim.

https://en.wikipedia.org/wiki/Shim_(computing)

"Shims can be used to support an old API in a newer environment,
or a new API in an older environment."

My reading of the discussion was to keep the older API to avoid changing the
OpenSSH code so a shim would be to support an "old API in a newer environment(OpenSSL-1.1)".

What we did was to convert OpenSC to the OpenSSL-1.1 API the write the shim
for "new API in an older environment".

Looking at your openssl_compat.h it looks like you have done something similar.
With OpenSC we only added the routines and defines we needed in OpenSC.

> 
> This is very similar to the approach taken by Kurt in his patch and to the work I did for OpenVPN
> ​ [1]​
> . And I also think it's the way to go since it will allow to diss older versions of openssl and/or libressl with minimal change in the Code That Matters while not being terribly difficult to maintain. 
> According to Kurt's patch, such a compat file for openssh would clock at roughly 500 lines of nearly trivial code (and I insist on this fact: code is quite trivial. The most complicated function would 
> be this one :
> 
> ​----8<-----​
> static int EVP_MD_CTX_reset(EVP_MD_CTX *ctx)
> {
> ​​
> if (ctx == NULL)
> ​​
> return 1;
> ​​
> /*
> ​​
> * Don't assume ctx->md_data was cleaned in EVP_Digest_Final, because
> ​​
> * sometimes only copies of the context are ever finalised.
> ​​
> */
> ​​
> if (ctx->digest && ctx->digest->cleanup
> ​​
>     && !EVP_MD_CTX_test_flags(ctx, EVP_MD_CTX_FLAG_CLEANED))
> ​​
> ctx->digest->cleanup(ctx);
> ​​
> if (ctx->digest && ctx->digest->ctx_size && ctx->md_data
> ​​
>     && !EVP_MD_CTX_test_flags(ctx, EVP_MD_CTX_FLAG_REUSE)) {
> ​​
> OPENSSL_clear_free(ctx->md_data, ctx->digest->ctx_size);
> ​​
> }
> ​​
> EVP_PKEY_CTX_free(ctx->pctx);
> #ifndef OPENSSL_NO_ENGINE
> ​​
> ENGINE_finish(ctx->engine);
> #endif
> ​​
> OPENSSL_cleanse(ctx, sizeof(*ctx));
> 
> ​​
> return 1;
> }
> ​---->8-----
> 
> 
> Other functions are getter and setters such as :
> 
> ​----8<-----​
> void DH_get0_key(const DH *dh, const BIGNUM **pub_key, const BIGNUM **priv_key)
> {
> if (pub_key != NULL)
> *pub_key = dh->pub_key;
> if (priv_key != NULL)
> *priv_key = dh->priv_key;
> }
> 
> int DH_set0_key(DH *dh, BIGNUM *pub_key, BIGNUM *priv_key)
> {
> /* If the field pub_key in dh is NULL, the corresponding input
> * parameters MUST be non-NULL.  The priv_key field may
> * be left NULL.
> */
> if (dh->pub_key == NULL && pub_key == NULL)
> return 0;
> 
> if (pub_key != NULL) {
> BN_free(dh->pub_key);
> dh->pub_key = pub_key;
> }
> if (priv_key != NULL) {
> BN_free(dh->priv_key);
> dh->priv_key = priv_key;
> }
> 
> return 1;
> }
> 
> ​int RSA_bits(const RSA *r)
> {
> return (BN_num_bits(r->n));
> }
> ​---->8-----
> 
> 
> There are some simple security​-related functions such as OPENSSL_zalloc() or OPENSSL_clean_free() but these functions are quite simple too (and the reasoning behind them is, I assume, well known).
> 
> 
> BR,
> 
> -- Emmanuel Deloget
> 
> ​[1] https://github.com/OpenVPN/openvpn/blob/master/src/openvpn/openssl_compat.h
> ​

-- 

  Douglas E. Engert  <DEEngert at gmail.com>