Re: [TLS] Fwd: Re: AD review of draft-ietf-tls-dtls-connection-id-07

[Achim Kraus <[e-mail]>]

Hi Ekr,

> As for EtM
>
> Encrypt-then-MAC:
> struct {
>    uint8 marker = tls12_cid;
>    uint8 cid_len;
>    uint8 content_type = tls12_cid;      \
>    uint16 DTLSCiphertext.version;       |  appears on wire
>    uint64 seq_num; // includes epoch    |
>    opaque cid[cid_len];                 /
>    uint16 iv_length;
>    opaque IV[iv_length];
>    uint16 enc_content_length;
>    opaque enc_content[enc_content_length];
> };
>

I failed to understand the reasons behind this proposal.

1. Why should the "marker" be added, if the "content_type" is already in
the MAC, and this special MAC is only applied for tls12_cid records.
What is the intended benefit of that?

2. Why should a "uint16 iv_length" be added?
2.a If it should be added, why as "uint16" instead of "uint8"
2.b If it should be added, why in the middle? It's not on the wire and
so I would assume, if at all, to have that at the begin.

best regards
Achim Kraus