[Ovmsdev] openssh 6.7 cipher aes128-cbc

Stephen Casner casner at acm.org
Fri Apr 27 13:16:11 HKT 2018

On Thu, 26 Apr 2018, Robin O'Leary wrote:

> On Fri, Apr 20, 2018 at 11:39:18PM -0700, Stephen Casner wrote:
> > On Fri, 20 Apr 2018, Robin O'Leary wrote:
> > > OK, so that started me on quite an adventure in to compiler errors
> > > and git submodules,
> > Sorry, did my commit of an update to mongoose trip you up?
> That was just one of several things, but one of the easily resolved ones!
> Much more annoying was a mysterious error about an undefined reference to
> "_impure_ptr", since that appears nowhere in the code.  I tracked it
> down to the fprintf in wolfssh/src/log.c; I still don't understand why,
> but I just commented it out, as ovms uses logFunction instead.

Oh, I do remember hitting that one myself and having to use Google for
help.  I think I hit that when I tried to add a printf statement of my
own, so maybe if I saw it when enabling DEBUG_WOLFSSH I used the same
workaround that you did.  I had not remembered that problem when
suggesting that you try DEBUG_WOLFSSH.  Sorry.

> > Perhaps I
> > should configure in the debug code for wolfssh and wolfssl by default
> > so the extra logging can be enabled whenever it is needed.
> Adding more calls to GetErrorString() in ssh.c is probably more helpful.

That is done, but there is only one error code that is returned for
any cipher, MAC or key mismatch, so DEBUG_WOLFSSH is still required to
figure out which one.

> It would be good to have a menu config option to define DEBUG_WOLFSSH.

I think the only penalty for enabling it always is an increase in code
size, ssuming the "_impure_ptr" is fixed in some way.  I asked Mark if
that would be reasonable to enable always.

> > WolfSSH also supports aes128-ctr and aes128-gcm, but I was warned that
> > the latter is much more expensive in speed and memory, so I excluded
> > it from the configuration for compilation.
> I think there is full support for aes128-ctr in wolfssl/wolfcrypt, but
> the places where it needs to be in wolfssh seem to be mostly missing.
> I had a go at adding it, but I haven't got it working.  It does connect,
> but auth always fails.  I haven't had chance to figure out why yet.

wolfssh/src/internal.c does reference AES128_CTR in a few places, but
I'm not sure what actions are required.

I started with WolfSSH 1.1.0 when doing the integration into OVMS.
There is a 1.2.0 release out now (on github at wolfSSL/wolfssh), and a
1.3.0 release pending that will include Wolf's integration of my SCP
additions back into their code base.

                                                        -- Steve

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