We need the length field so that calling the function with different
lengths results in different outputs. Not that anyone should be doing
that, of course.
On 6 July 2017 at 14:06, Kazu Yamamoto <k...@iij.ad.jp> wrote:
>>> HKDF-Expand-Label(Secret, Label, *Value*, Length) =
>>> HKDF-Expand(Secret, HkdfLabel, Length)
>>>
>>> struct {
>>> uint16 length = *Value.length*;
>>> opaque label<7..255> = "tls13 " + Label;
>>> opaque hash_value<0..255> = *Value*;
>>> } HkdfLabel;
>>
>> Length is the size of the output, so you don't want to assign
>> Value.length to that field in the struct.
>
> Yes. I would remove the "length" field, too.
>
>> Also, you forgot to rename hash_value in the struct.
>
> You are right.
>
> --Kazu
>
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