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From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no>
To: freebsd-security <freebsd-security@freebsd.org>
Cc: RW <rwmaillists@googlemail.com>
Subject: Re: Two Dumb Questions
References: <32084.1474872154@segfault.tristatelogic.com>
 <20160926135238.6296ddc2@gumby.homeunix.com>
Date: Mon, 26 Sep 2016 22:48:12 +0200
In-Reply-To: <20160926135238.6296ddc2@gumby.homeunix.com> (RW via
 freebsd-security's message of "Mon, 26 Sep 2016 13:52:38 +0100")
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RW <rwmaillists@googlemail.com> writes:
> There's a simple paint analogy here:
>
>  https://en.wikipedia.org/wiki/Diffie=E2=80=93Hellman_key_exchange
>
> that illustrates how it's possible to exchange a shared secret without
> an eavesdropper knowing what it is. The shared secret can then be used
> for symmetric encryption using something like AES.

SSL / TLS didn't commonly use DH, much less *safe* DH, until fairly
recently, and DH alone is not very useful.  You need either a shared
secret or trusted key pairs to authenticate either or both endpoints.

> Actual protocols use public key cryptography so it can be established
> that the exchange is end to end, and not broken into two separate
> exchanges.

Assuming you can trust the public key, which is what CAs are for, but
CAs can be hacked, deceived or coerced.

DES
--=20
Dag-Erling Sm=C3=B8rgrav - des@des.no