[racket-dev] [patch] OpenSSL ECDH(E) + DHE support.

From: Edward Lee (e45lee at uwaterloo.ca)
Date: Mon Feb 10 20:36:02 EST 2014

On Mon, Feb 10, 2014 at 06:37:56PM -0500, Ryan Culpepper wrote:
> On 02/08/2014 05:52 PM, Edward Lee wrote:
> >Hi.
> >
> >Racket's OpenSSL bindings do not currently enable the ECDH(E) and the
> >DHE ciphers, which are needed for perfect forward secrecy.
> >
> >I've attached a patch that:
> >   - Embeds reasonable defaults for DHE mode.
> >   - Adds two functions, ssl-server-context-enable-dhe! and
> >     ssl-server-context-enable-ecdhe! that when given
> >     DHE/ECDHE setup arguments (for DHE, a DH parameter file path,
> >     for ECDHE, the name of one of the built-in OpenSSL elliptic curves
> >     [currently, only secp521r1])
> >   - (unrelated, but also useful) Adds bindings for TLS 1.1/1.2-only
> >     server/client contexts.
> >
> >This patch is currently a work in progress (it currently only supports
> >one elliptic curve name) that works well enough for what I am using it
> >for, but I'm interested in getting this patch upstream.
> Here are a few comments:
> What is SSL_CTRL_SET_ECDH_AUTO? I couldn't find it in the openssl
> headers, and I searched a few recent versions. It seems unused here,
> anyway.
It's not defined in OpenSSL 1.0.1, I think.  It can be used for enabling
ECDH(E) in OpenSSL >= 1.0.2, with OpenSSL automatically selecting the
curve - <https://www.openssl.org/news/changelog.html>, "Support for
automatic EC temporary key parameter selection..."
> I think it would be better to read the DH params file into memory
> using Racket file operations and then use a memory BIO for
> PEM_read_bio_DHparams. Two reasons: the file access will then
> automatically go through Racket's security-guard checks, and the
> file read will go through Racket's IO system, so if the read blocks
> it won't block all Racket threads.
I will investigate this, and time permitting, will change my patch to
use Racket's IO system for loading the parameters.
> In ...enable-ecdhe!, the 'case' form doesn't need 'quote'. It should
> be this instead:
>   (case name
>     [(secp521r1) NID_secp521r1]
>     [else ___])
> As it is, the function will accept 'quote as the name of a curve.
Thanks for pointing this out.
> >What's the exact process for this?
> If you have a github account, you can fork the repo there and submit
> a pull request. But we can certainly handle patches like this too.
> Ryan
Great, thanks.


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