Skip to content

Clarify Key for PSKBinderEntry #1395

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 1 commit into
base: main
Choose a base branch
from
Open

Clarify Key for PSKBinderEntry #1395

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
16 changes: 12 additions & 4 deletions draft-ietf-tls-rfc8446bis.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -790,7 +790,7 @@ CertificateVerify:

Finished:
: A MAC (Message Authentication Code) over the entire handshake.
This message provides key confirmation for the shared secrets established in the handshake
This message provides key confirmation for the shared secrets established in the handshake,
binds the endpoint's identity to the exchanged keys, and in PSK mode
also authenticates the handshake. \[{{finished}}]
{:br }
Expand Down Expand Up @@ -2785,10 +2785,18 @@ length, the length of the extensions block, and the length of the
"pre_shared_key" extension) are all set as if binders of the correct
lengths were present.

The PskBinderEntry is computed in the same way as the Finished
message ({{finished}}) but with the BaseKey being the binder_key
The key for PskBinderEntry is computed in the same way as the finished_key
({{finished}}) but with the BaseKey being the binder_key
derived via the key schedule from the corresponding PSK which
is being offered (see {{key-schedule}}).
is being offered (see {{key-schedule}}), i.e.:

~~~
HKDF-Expand-Label(binder_key, "finished", "", Hash.length)
~~~

The PskBinderEntry value is then generated from this key
in the same way as the Finished message ({{finished}}) with the
Transcript-Hash as explained below.

If the handshake includes a HelloRetryRequest, the initial ClientHello
and HelloRetryRequest are included in the transcript along with the
Expand Down