Hi Pieter,
On 04/04/19 09:34, Pieter Hulshoff wrote:
Hello all,
I was wondering: with regards to the
TLS-DHE-RSA-WITH-AES-256-GCM-SHA384 TLS cipher suite, what exactly is
the SHA-384 used for? I would assume that the AES-256-GCM already
takes care of the data path encryption and authentication, so it's not
clear to me what the SHA-384 in the name refers to.
this name can be (partially) found in the OpenSSL source code. The
OpenSLS naming convention for TLS ciphers consists of a few parts:
uint32_t algorithm_mkey; /* key exchange algorithm */
uint32_t algorithm_auth; /* server authentication */
uint32_t algorithm_enc; /* symmetric encryption */
uint32_t algorithm_mac; /* symmetric authentication */
so the TLS cipher name includes names for both symmetric encryption and
symmetric authentication *separately* : with GCM ciphers you do both of
them in one go, but the TLS cipher still lists them separately. This TLS
cipher name is also the most common cipher name seen in Apache SSL logs,
e.g.
ECDHE-RSA-AES128-GCM-SHA256
Also note that this cipher is the cipher used for the *control channel*,
not for the data channel and is the result of the "regular" TLS
negotiation that happens when the control channel is established.
HTH,
JJK
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