[TLS] Key Hierarchy TLS 1.3 RFC8446(bis)

[Muhammad Usama Sardar <[e-mail]>]

Hi all,

In the key schedule (section 7.1) of RFC8446(bis), what is the rationale 
for using /*Derive-Secret(., "derived", "")*/in the derivations of 
Handshake and Master Secrets? Since this change was made in draft 19, I 
expect there should be some reasoning of why this was added. 
Specifically, what are the security implications if this step is missed, 
i.e.,

  * if Early Secret is directly used as the Salt argument for
    HKDF-Extract of Handshake Secret;
  * and similarly if Handshake Secret is directly used as the Salt
    argument for HKDF-Extract of Master Secret.

Regards,

Usama