Hi Mirja,
please see inline. The draft is already in RFC Editor's queue, so please
see our reasonings for addressing your comments (we add one clarifications
and ignored two other cases, please see why).
Regards,
Valery.
Hi Valery,
sorry for the late reply (holidays :-) )
See below.
On 25.09.2016 22:20, Valery Smyslov wrote:
Hi Mirja, Yoav,
I agree with Yoav's answers, just want to clarify a few things. See below
(I removed the comments where I have nothing to add to Yoav's answers).
----------------------------------------------------------------------
COMMENT:
----------------------------------------------------------------------
Some questions:
1) sec 7.1.2: If there is a puzzle but no cookie, maybe the initiator
should ignore it and try to send reply without the puzzle solution, as
there might be still a change to get served…? If it then received another
packet with puzzle it can still solve it and reply.
A response that contains neither COOKIE nor INVALID_KE_PAYLOAD nor the regular
payloads like SA is invalid according
to RFC 7296.
That is one reason why we chose to keep the COOKIE notification and add a
PUZZLE notification rather than put both
pieces of
data in the new notification. A response with only PUZZLE and no COOKIE is
invalid and should be treated as such.
So after some (not specified anywhere) time, the Initiator should start a new
IKE_SA_INIT exchange, hoping that this
time the
Responder returns a valid response.
Actually, the Initiator sends requests, not responses. So, if the Initiator
ignores
invalid response from the Responder, then the only thing it can do is to wait
some time and sends another request (or just retransmit the sent request in hope
that invalid response was from an attacker who wants to break IKE SA
establishment).
If the situation doesn't improve (the Initiator continues to receive invalid
responses),
then the Initator has nothing to do but give up.
I just want to emphasise that Mirja's suggestion (ignore invalid response) is
exactly
what the draft suggests to do in this case, as Yoav correctly outlined. Isn't
it clear enough from the
document? Should we add more clarifications?
I guess add one sentence stating this explicitly cant hurt?
I think the draft is very clear:
In this case the
Initiator MUST ignore the received message and continue to wait until
either a valid PUZZLE notification is received or the retransmission
timer fires. If it fails to receive a valid message after several
retransmissions of IKE_SA_INIT requests, then it means that something
is wrong and the IKE SA cannot be established.
This text is completely in line with RFC7296 (Section 2.21.1):
Because all error notifications are completely
unauthenticated, the recipient should continue trying for some time
before giving up. The recipient should not immediately act based on
the error notification unless corrective actions are defined in this
specification, such as for COOKIE, INVALID_KE_PAYLOAD, and
INVALID_MAJOR_VERSION.
They both tell that the Initiator must not act immediately on receiving
malformed packet or error notification in IKE_SA_INIT since this
packets are unauthenticated. Instead, the Initiator must try to
get a valid response by retransmitting the request for some time
and give up only if no valid response is received.
So, I frankly don't see how we can improve the text. If you have
the text you think is really important to add, then please provide it.
3) also sec 7.1.4: Does the following sentence really makes sense? How
doe the responser know? Maybe just remove it?
„The more time the Initiator spent solving the puzzles, the higher
priority it should receive.“
The Responder cannot know. It can only assume based on the expected number of
steps in finding a solution with a
certain number of trailing zero bits.
The Responder can also measure the time between the puzzle request and
the reception of puzzle solution (and the Responder can do this in a stateless
manner).
Sure this measurment cannot be accurate, because it includes RTT, but it
can be used as additional input to the prioritizing algorithm (along
with puzzle difficulty and the number of times the puzzle was requested).
But in general the prioritizing algorithm is a local matter of Responder
and the draft doesn't mandatae it in any way.
In this case I would recommend a short warning that if the response time is measured as an estimated for the
processing time, network delay should be taken into account.
The Responder has no reliable means to separate RTT
from the time the Initiator spent for solving the puzzle.
The Responder can only suggest that if, for example, the puzzle solution
was returned in 10 seconds, then it probably took ~9 seconds for solving
the puzzle and ~1 second for network delay. But it could happen that
network quality is poor and in reality the figures are just opposite.
Since the Responder cannot reliably "distill" CPU consumption time,
I think this warning wouldn't help implementers. The time spent for solving a
puzzle
is just an additional input data for Responder's decision, but definitely
not the primary one, which is the puzzle's difficulty.
5) sec 7.2.2 says „If the IKE_SA_INIT response message contains the
PUZZLE notification and the Initiator supports puzzles, it MUST solve the
puzzle.“
Should this be „IKE_SA_AUTH“ here instead of „IKE_SA_INIT“?
Otherwise it contradicts sec 7.1.2 („The Initiator MAY ignore the PUZZLE
notification…“)
Sure. Seems to be a typo.
No, that's not a typo. Note, that unlike IKE_SA_INIT exchange the IKE_AUTH
exchange
cannot be restarted. So, if we want the puzzle solution to be in IKE_AUTH
request
(that is sent by the Initiator), the puzzle must be given to the Initiator
earlier,
i.e. in the preceding response from the Responder, i.e. in the IKE_SA_INIT
response.
So the text is correct.
However, I understand Mirja's source of confusion - in IKEv2 there are
three different kinds of IKE_SA_INIT responses ("regular", COOKIE and
INVALID_KE_PAYLOAD) and unfortunately RFC7296 doesn't give them distinct
names - they all are IKE_SA_INIT response. So, there is no contradiction with
7.1.2, because 7.1.2 tells about IKE_SA_INIT response that contain COOKIE
request
(and PUZZLE request), while 7.2.2 tells about "regular" IKE_SA_INIT response,
i.e. that contains SA, KE, NONCE payloads etc. So, while in the first case
the Initiator can ignore puzzle request (if PUZZLE is present in a response
containing COOKIE)
and still have a chance to be served, in the second case it cannot ignore
puzzle request
(when PUZZLE is present in a "regular" IKE_SA_INIT response).
Do you think it is not clear enough and more clarifications are needed?
If it's possible to clarify this without data to much text about RFC7296 that
would clearly help!
We've added a clarification in 7.2.2 that regular IKE_SA_INIT response is meant
(containing SA, KE, NONCE etc. payloads).
Thanks,
Mirja
Regards,
Valery.
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