Hi Jan Just,

On 07-11-18 15:50, Jan Just Keijser wrote:
> AES-256-GCM:
> 
> crypto_adjust_frame_parameters:
>    packet_id_size= 4 bytes
>    cipher_kt_iv_size = 12 bytes
>    cipher_kt_tag_size = 16 bytes
>    cipher_kt_block_size = 16 bytes
>    hmac_length = 0 bytes
> crypto_adjust_frame_parameters: Adjusting frame parameters for crypto by
> 48 bytes

Hm, this is indeed what OpenVPN does, but I think it's wrong. In AEAD
mode we should not adjust for the IV size, because we only send the
packet ID on the wire. It seems that nobody has noticed that before.

So now we have to consider whether we can fix that without even more
surprising side effects, like peers disagreeing on the correct link/tun
mtu...

-Steffan


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