Re: [PATCH RFC net-next 1/5] tls: add HKDF-Expand-Label for the TLS 1.3 key schedule

[Martin Belanger]

On 10/26/26 03:27, Hannes Reinecke wrote:
> On 10/26/26 1:36 AM, Martin Belanger via B4 Relay wrote:
> > From: Martin Belanger <martin.belanger@xxxxxxxx>
> >
> > A TLS 1.3 KeyUpdate derives the next traffic secret, key and IV with
> > HKDF-Expand-Label (RFC 9846, section 7.2). Add the helper for the
> > kernel to do this itself.
> >
> > Only the part of the key schedule after the handshake is needed. The
> > input is a traffic secret, which is already a pseudorandom key, so
> > HKDF-Extract is not needed. Each output is at most Hash.length bytes,
> > so each derivation is a single HMAC with the library SHA-256 or SHA-384
> > functions.
> >
> > Assisted-by: LLM
> > Signed-off-by: Martin Belanger <martin.belanger@xxxxxxxx>
> > ---
> >   net/tls/Kconfig    |  2 ++
> >   net/tls/Makefile   |  2 +-
> >   net/tls/tls.h      |  2 ++
> >   net/tls/tls_hkdf.c | 82 
> > ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >   4 files changed, 87 insertions(+), 1 deletion(-)
> And another HKDF implementation. Maybe it's time to split if off (again).
> But anyway.
Yes. crypto/hkdf.c went away again in 6d888db2cfd9 ("crypto: remove
HKDF library"), when fscrypt and nvme-auth moved to the HMAC library.
tls_hkdf.c follows that pattern. It needs only HKDF-Expand-Label, which
is one HMAC here. If a shared helper is wanted again, I would do it in
a separate series.

Thanks for the review.

Martin

> Reviewed-by: Hannes Reinecke <hare@xxxxxxxxxx>
>
> Cheers,
>
> Hannes