aes_cbc_hmac_sha1 implementation

[Matt Caswell]

On 27/02/2020 18:30, Phani 2004 wrote:
> Thanks for the reply.
> 
> In ssl_get_evp_cipher api when etm flag is enabled the
> aesni_cbc_hmac_sha1_cipher is not used. In this cipher only it
> implements mte. This part is not clear to me? Support I implement one
> cipher func which needs to handle both etm as well as mte, at the cipher
> api level how do I know if we have etm extension enabled or not.

At the engine level all it knows about are ciphers and hashes. Engines
know nothing about TLS ciphersuites or TLS extensions. Your engine will
not know whether etm or mte is in use. libssl makes the decision about
what cipher it is going to ask the engine for based on what has been
negotiated.

If mte is in use then it will first look to see if it has an
implementation of "AES-128-CBC-HMAC-SHA1" (of which
aesni_cbc_hmac_sha1_cipher is the built-in implementation).

If that is not available it will look for individual implementations of
"AES-128" and "SHA1".

If etm is in use it will just look for individual implementations of
"AES-128" and "SHA1".

Matt



> 
> Regards
> Phani
> 
> On Wed, 26 Feb, 2020, 6:03 PM Hubert Kario, <hkario at redhat.com
> <mailto:hkario at redhat.com>> wrote:
> 
>     On Wednesday, 26 February 2020 08:59:01 CET, Phani 2004 wrote:
>     > Thanks for the quick response Matt.
>     >
>     > My command was :
>     > openssl s_client -connect 10.29.20.26 -cipher ECDHE-RSA-AES128-SHA
>     -tls1_2.
>     > I did not realise that "2" was not copied.
>     >
>     > I am trying to implement combined algo support on our engine.
>     > I am using the openssl s_server and s_client apps to validate my
>     > implementation.
>     > The combined algo that i am looking to implement is AES128/256 and
>     SHA1.
>     > Its clear that i should always use tls version less than 1.3
>     otherwise GCM
>     > ciphers are used.
>     >
>     > What cipher suites can i use to validate the above combination of
>     combined
>     > algo?
> 
>     OpenSSL internally treats key exchange and symmetric cipher
>     separately, so
>     all "*AES128-SHA" ciphers use the same cipher backend
> 
>     you should also test AES256-SHA, AES128-SHA256, AES256-SHA256 and
>     AES256-SHA384
> 
>     > Which tls versions support which cipher suites?
> 
>     *-SHA1 and *MD5 is supported by everything between SSL3 and TLS 1.2
>     *-SHA256 and *-SHA384 (if they are not TLS1.3 cipher suites) are
>     supported
>     by TLS 1.2 only
> 
>     > Should i be doing "encrypt-then-mac" or "mac-then-encrypt" in my
>     > implementation?
>     > Does the cipher suite decide this?
>     > If yes, what are the ciphers which do "encrypt-then-mac" and what
>     ciphers
>     > to "mac-then-encrypt"?
> 
>     etm vs mte happens based on negotiated extension, not cipher suite
> 
>     -- 
>     Regards,
>     Hubert Kario
>     Senior Quality Engineer, QE BaseOS Security team
>     Web: www.cz.redhat.com <http://www.cz.redhat.com>
>     Red Hat Czech s.r.o., Purkyňova 115, 612 00  Brno, Czech Republic
>