[openssl-users] Diffie-Hellman Questions
norm.green at gemtalksystems.com
Tue May 24 17:33:42 UTC 2016
Thanks Rich. More newbie questions.
Looking at the available ciphers I see this:
>./openssl ciphers -v 'ALL:aNULL' |grep ECDH |grep "Au=None"
AECDH-AES256-SHA SSLv3 Kx=ECDH Au=None Enc=AES(256) Mac=SHA1
AECDH-AES128-SHA SSLv3 Kx=ECDH Au=None Enc=AES(128) Mac=SHA1
AECDH-RC4-SHA SSLv3 Kx=ECDH Au=None Enc=RC4(128) Mac=SHA1
AECDH-DES-CBC3-SHA SSLv3 Kx=ECDH Au=None Enc=3DES(168) Mac=SHA1
AECDH-NULL-SHA SSLv3 Kx=ECDH Au=None Enc=None Mac=SHA1
1) What arg to SSL_CTX_set_cipher_list() to I need to use to get these?
I previously tried "kEECDH:kEDH" and that didn't work.
2) These ciphers all report as SSLv3. Do I have to use SSLv3
client/server methods to get access to these ciphers? I was using TLS
1.2 (TLSv1_2_server_method()) methods.
On 5/24/16 10:08, Salz, Rich wrote:
>> 1) The wiki says don't use ADH, presumably because ADH provides
>> encryption but not authentication and is exposed to man in the middle
>> attacks. Is that the only reason?
> Use ECDH, it's less expensive computationally.
>> 2) Are the same encryption keys used every time with ADH?
> Yes. That's the other BIG reason :) You really want ephemeral, and therefore ECDH
>> 3) Is it possible to use ephemeral DH without using certificates? I was not
>> able to get that to work.
> Yes. This is "null" auth.
>> 4) What is the best practice for establishing an anonymous encrypted
>> channel using OpenSSL?
> Postfix does this kind of thing, as does other SMTP software. Look around for 'opportunistic encryption' perhaps.
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