Dear Benjamin
Many thanks for your in depth review!
Considering the amount of changes I published 16 just to make a statement of
the current exchange.
https://www.ietf.org/rfcdiff?url2=draft-ietf-6lo-ap-nd-16
Hopefully this should make you validation of the proposed changes easier.
Please see below for the discussion:
----------------------------------------------------------------------
DISCUSS:
----------------------------------------------------------------------
The CIPO description specifies that a 5-bit Reserved1 field and a 13-bit Public
Key Length field are combined to fit into a 16 (not 18)-bit space.
(The Figure shows the Public Key Length field as 11 bits.)
My bug, when I address Eric's review; the key length is expressed as 11 bits,
so the max size for a key is 2K bytes.
Beyond that it will not fit in the ND option format and we will need to
fragment it.
Why do we need to allow ambiguity/flexibility as to the point representation
within a given Crypto-Type value (as opposed to fixing the representation as a
parameter of the Crypto-Type)? Alternately, what does "(un)compressed"
mean, as it's not really clarified directly? Furthermore, Table 2 lists an
"(un)compressed" representation for type 0 (over P-256), but RFC 7518 notes
that the compressed representation is not supported for P-256 (Section
6.2.1.1). I also am not finding the needed codepoints registered in the JOSE
registries to use ECDSA25519 (crypto-type 2) -- do we need to register
anything there?
Let us take this one separately in a thread with the co authors
Per my comment on Section 4.4, there may be some implicit
expectation/requirement of 128+-bit ROVRs for AP-ND, but I didn't find where
such a requirement was stated.
Suggest to add at the end of 4.1
"
At the time of this writing, a minimal size for the Crypto-ID of 128
bits is RECOMMENDED. This value is bound to augment in the future.
"
The ROVR is only a consequence I guess
----------------------------------------------------------------------
COMMENT:
----------------------------------------------------------------------
Thanks for this well-written document!
Thank *you*! Your reviews are always incredible. Really, really appreciated.
It will be good to see this stuff getting deployed.
Indeed! It is much simpler to do than SEND, still it will take a bit of
persuading needed to progress this into the products and stacks.
What's the risk of DoS via (short) address exhaustion in terms of 6LBR
resources (as distinct from 6LR resources mentioned at the end of Section 7.1)?
Indeed an issue that implementation have to look as.
Short addresses are a trick that 802.15.4 introduces to build shorter frames.
I'd like to avoid mentioning them specifically since now 6Lo applies to a great
many MACs and PHYs. I think your point is that using short addresses provides a
hard 64K boundary for the pool of address.
RFC 8505 has:
The registration mechanism may be used by a rogue node to attack the
6LR or 6LBR with a denial-of-service attack against the registry. It
may also happen that the registry of a 6LR or 6LBR is saturated and
cannot take any more registrations; this scenario effectively denies
the requesting node the capability to use a new address.
Suggestion to grow section 7.2 as follows:
7.2. Related to 6LoWPAN ND
The threats and mediations discussed in 6LoWPAN ND [RFC6775][RFC8505]
also apply here, in particular denial-of-service attacks against the
registry at the 6LR or 6LBR.
Secure ND [RFC3971] forces the IPv6 address to be cryptographic since
it integrates the CGA as the IID in the IPv6 address. In contrast,
this specification saves about 1Kbyte in every NS/NA message. Also,
this specification separates the cryptographic identifier from the
registered IPv6 address so that a node can have more than one IPv6
address protected by the same cryptographic identifier.
With this specification the 6LN can freely form its IPv6 address(es)
in any fashion, thereby enabling not only 6LoWPAN compression for
IPv6 addresses that are derived from Layer-2 addresses, but also
temporary addresses, e.g., formed pseudo-randomly and released in
relatively short cycles for privacy reasons [RFC8064][RFC8065]. This
specification provides added protection for addresses that are
obtained following due procedure [RFC8505] but does not constrain the
way the addresses are formed or the number of addresses that are used
in parallel by a same entity. A rogue may still perform denial-of-
service attack against the registry at the 6LR or 6LBR, or attempt to
deplete the pool of available addresses at Layer-2 or Layer-3.
Section 1
In this specification, a 6LN generates a cryptographic ID (Crypto-ID)
and places it in the ROVR field during the registration of one (or
more) of its addresses with the 6LR(s). Proof of ownership of the
Crypto-ID is passed with the first registration exchange to a new
6LR, and enforced at the 6LR. The 6LR validates ownership of the
cryptographic ID before it creates any new registration state, or
changes existing information.
I'll read on and see, but how much trust does this imply that we require of all
6LRs (as opposed to the 6LBR, which is kind of required to be pretty trusted)?
[ed.: basically complete trust is required]
Spot on. As you kept on reading you found that you analysis is exactly correct
and that we explain that in section 7.6.
We are taking steps towards zerotrust in RPL and ND, one at a time. The thing
you could not see there but will see next is
https://tools.ietf.org/html/draft-ietf-roll-unaware-leaves-09#section-3.2.3
From there we'll need to extend RPL to challenge along a path, and something
for the 6LBR as well. It all appears quite doable, but yet to be designed : )
The protected address registration protocol proposed in this document
enables Source Address Validation (SAVI) [RFC7039]. This ensures
that only the actual owner uses a registered address in the IPv6
source address field. A 6LN can only use a 6LR for forwarding
packets only if it has previously registered the address used in the
source field of the IPv6 packet.
nit: this last sentence is written as if we not only enable, but also require,
SAVI.
What about:
"
The protected address registration protocol proposed in this document
provides the same conceptual benefit as Source Address Validation
(SAVI) [RFC7039] that only the owner of an IPv6 address may source
packets with that address. As opposed to [RFC7039], which relies on
snooping protocols, the protection is based on a state that is
installed and maintained in the network by the owner of the address.
With this specification, a 6LN may use a 6LR for forwarding an IPv6
packets if and only if it has registered the address used as source
of the packet with that 6LR.
"
The 6lo adaptation layer in [RFC4944] and [RFC6282] requires a device
to form its IPv6 addresses based on its Layer-2 address to enable a
better compression. This is incompatible with Secure Neighbor
Discovery (SeND) [RFC3971] and Cryptographically Generated Addresses
(CGAs) [RFC3972], since they derive the Interface ID (IID) in IPv6
addresses with cryptographic keys.
Are we going to have some further discussion of the scope of that loss of
functionality and/or alternative mechanisms to achieve those goals, or is this
statement just intended to note the incompatibility?
Clarifying that this is a side note:
"
The 6lo adaptation layer in [RFC4944] and [RFC6282] requires a device
to form its IPv6 addresses based on its Layer-2 address to enable a
better compression. As a side note, this is incompatible with Secure
Neighbor Discovery (SeND) [RFC3971] and Cryptographically Generated
Addresses (CGAs) [RFC3972], since they derive the Interface ID (IID)
in IPv6 addresses from cryptographic keys.
"
Section 3
The proof requires the support of Elliptic Curve Cryptography (ECC)
and that of a hash function as detailed in Section 6.2. To enable
the verification of the proof, the registering node needs to supply
certain parameters including a Nonce and a signature that will
demonstrate that the node has the private-key corresponding to the
public-key used to build the Crypto-ID.
nit: the proof itself may only indirectly involve a hash, since we use non-
prehash Ed25519 (but the hash function is still needed to generate the Crypto-
ID itself).
Changed "proof" to " overall mechanism".
The point we want to make is that implementation cost and the code footprint,
which is a typical concern in constrained IOT.
nit(?): I think we tend to see "possesses the private key" more often than "has
the private-key", for parallelism with the "proof of possession" term of art.
Made the change
The elliptic curves and the hash functions that can be used with this
specification are listed in Table 2 in Section 8.3. The signature
scheme that specifies which combination is used is signaled by a
nit: this could be misread as saying that the Table is authoritative, not the
registry.
Clarifying questions:
- This spec is authoritative for listing the elliptic curves and the hash
functions that it supports, correct?
- The registry is authoritative for the setting of values, which may change if
this draft is obsoleted, is that your point?
From there I'm unsure what to do. The goal is to keep the focus on the bill of
material of what needs to be implemented.
If that helps I can add (values to be confirmed by IANA) as follows?
" The elliptic curves and the hash functions that can be used with this
specification are listed in Table 2 in Section 8.3. The signature
scheme that specifies which combination is used is signaled by a
Crypto-Type (values to be confirmed by IANA) in a new IPv6 ND Crypto-
ID Parameters Option (CIPO, see Section 4.3) that contains the
parameters that are necessary for the proof, a Nonce option
([RFC3971]) and a NDP Signature option (Section 4.4).
"
Section 4.1
The Crypto-ID is derived from the public key and a modifier as
follows:
1. The hash function indicated by the Crypto-Type is applied to the
CIPO. Note that all the reserved and padding bits MUST be set to
zero.
2. The leftmost bits of the resulting hash, up to the size of the
ROVR field, are used as the Crypto-ID.
This construction seems to allow for some malleability, in that an attacker who
observes a given Crypto-ID and CIPO could produce a related, valid, Crypto-ID
by reducing the ROVR length and truncating what was received. I haven't
attempted to explore what (if any) potential consequences there are of such
malleability, and would like to know if anyone else has already done so. It
looks like the NDPSO construction includes the length of the Crypto-ID, so it
would be hard for an attacker to do much with such a truncated Crypto-ID, but
attacks only get better...
The point is that the Crypto-ID remains in the 6LBR is its original form, size
and value. A shorted Crypto-ID is a different Crypto-ID even if bits match.
Truncated per se does not help vs. any other change.
Also, the attacker would have to be on path of the initial registration. If
that is so, and it wants to update the ROVR, it can do that a lot more.
Now, the crypto-ID dictates the size of the ROVR not the other way around, so I
fixed:
"
The leftmost bits of the resulting hash, up to the desired size, are used as
the Crypto-ID.
"
Anything else I should consider doing?
Section 4.2
nit: I confess I'm missing what compels us to produce a de novo definition of
the "Status" field (and Length field) as opposed to deferring to the RFC
8505 definition, as we do for most of the other fields.
True, it was just a copy. Changed to
Length: Defined in [RFC8505].
Status: Defined in [RFC8505].
Section 4.3
Crypto-Type: 8-bit unsigned integer. The type of cryptographic
algorithm used in calculation Crypto-ID (see Table 2 in
Section 8.3). Although the different signature schemes target
similar cryptographic strength, they rely on different curves,
hash functions, signature algorithms, and/or representation
conventions.
While the currently-defined signature schemes target similar cryptographic
strength, do we need to imply that all future ones will also target a similar
strength (especially since Section 8.3 admits the possibility of "better
security")?
Certainly, the intention was not to imply that for the future, just a remark on
the current.
Moved text from there into the presentation before the figure, as
"
* This specification uses signature schemes which target similar
cryptographic strength but rely on different curves, hash
functions, signature algorithms, and/or representation
conventions. Future specification may extend this for different
cryptographic algorithms and longer keys, e.g., to provide a
better security properties or a simpler implementation.
"
-----------------------------------------
Modifier: 8-bit unsigned integer. Set to an arbitrary value by the
creator of the Crypto-ID. The role of the modifier is to enable
the formation of multiple Crypto-IDs from a same key pair, which
reduces the traceability and thus improves the privacy of a
constrained node that could not maintain many key-pairs.
It may be worth digging in a little further to the threat model being addressed
here -- while I laud the ability to have multiple Crypto-IDs from a single
keypair,
it seems that the tracking-prevention this affords implies an attacker who can
observe Crypto-IDs, most likely at multiple points in the network. Are Crypto-
IDs used for anything other than EAROs?
No, to my best knowledge the crypto ID is not used elsewhere so far.
I don't have a great sense for how
likely it is that an attacker in position to observe (a subset of) EAROs would
not
But with the backbone router work everyone on the backbone will see it (see
https://datatracker.ietf.org/doc/draft-ietf-6lo-backbone-router/). The goal
here is to avoid an easy correlation between several addresses owned by a same
node. Note that the Routing Proxy enable the 6BBR to provide its own SLLAO to
the nodes on the backbone so many nodes may be hidden behind a same MAC address
also be in a position to observe at least one associated CIPO, which includes
all
the information needed to generate the Crypto-ID other than the Modifier.
The CIPO for now does not circulate over the network but is contained between
6LR and 6LN.
With only an 8-bit Modifier space, brute-forcing the other possible Crypto-IDs
for that keypair is not terribly strenuous, whereas allowing for a (potentially
But the point is that the attacker does not have the public key.
variable length?) larger Modifier, say 64 bits, would substantially increase the
work-factor needed to predict (and store!) other Crypto-IDs that might be used
Yes but at the same time it makes it easier to brute-force forge a Crypto-ID
that has the same value as the one of the owner from a different key by
rotating the large Modifier on a same key, as opposed to forming new keys.
for this keypair. Given that the CIPO already carries the public key itself,
it's
not entirely clear how space-constrained we are so as to limit this to just
8 bits of modifier.
Open to change, but with the current balance with the CIPO local to the 6LN /
6LR I'm not convinced it's a good idea.
Please let me know if you want to continue on that topic and we'll make it a
thread.
------------------
Padding: A variable-length field completing the Public Key field to
align to the next 8-bytes boundary.
(MUST be set to zero by sender and ignored by receiver, as well?)
Done
The implementation of multiple hash functions in a constrained
devices may consume excessive amounts of program memory.
But multiple signature algorithm implementations will not?
draft-ietf-lwig-curve-representations discussed in the next section enables to
factorize code, if I understand well.
But to your point, what about the following clarification:
"
The implementation of multiple hash functions in a constrained
devices may consume excessive amounts of program memory. This
specification enables the use of SHA-256 [RFC6234] for all the
supported ECC curves.
Some code factorization is also possible for the ECC computation
itself. [CURVE-REPRESENTATIONS] provides information on how to
represent Montgomery curves and (twisted) Edwards curves as curves in
short-Weierstrass form and illustrates how this can be used to
implement elliptic curve computations using existing implementations
that already provide, e.g., ECDSA and ECDH using NIST [FIPS186-4]
prime curves.
For more details on representation conventions, we refer to
Appendix B.
"
Section 4.4
Is there some more discussion to have about how NDPSO includes only a
specific fixed set of information under the signature but RSAO signs all options
that appear prior to it in the message?
Does not hurt to add it. The text in 4.4 would now look like
"
As opposed to the RSA Signature Option (RSAO) <...>
Another difference is that the NDPSO signs a fixed set of fields as
opposed to all options that appear prior to it in the that bears the
signature. This allows to elide a CIPO that the 6LR already
received, at the expense of the capability to add arbitrary options
that would signed with a RSAO. "
nit: style suggests parallelism between the Section 4.3 and 4.4 introductory
remarks (e.g., "this specification defines the NDP Signature Option (NDPSO)").
Added:
"
This specification defines the NDP Signature Option (NDPSO). The
NDPSO carries the signature that proves the ownership of the Crypto-ID.
"
As opposed to the RSA Signature Option (RSAO) defined in section 5.2.
of SEND [RFC3971], the NDPSO does not have a key hash field. The
hash that can be used as index is the 128 leftmost bits of the ROVR
field in the EARO.
nit: this last sentence perhaps leaves more context implicit than the reader
might like; I suggest "Instead, the leftmost 128 bits of the ROVR field in the
sibling EARO are used to lookup the key used for signature verification, [left-
padded with zeros if needed]". (I added the part in square brackets because
I'm not sure that anything guarantees the ROVR will actually contain
128 bits -- when AP-ND is not in use its typically just 64 bits, right?)
Per your comment we recommend 128 bits minimum. Keeping it at 64 bits was not
the intention.
Not sure why you meant by sibling; the text would become
"
As opposed to the RSA Signature Option (RSAO) defined in section 5.2.
of SEND [RFC3971], the NDPSO does not have a key hash field.
Instead, the leftmost 128 bits of the ROVR field in the EARO are used
to retrieve the CIPO that contains the key material used for signature
verification, left-padded if needed.
"
Pad Length: 8-bit unsigned integer. The length of the Padding
field.
(In octets?)
Actually it's probably better for this field and the below to move to the way
we did the previous option
More below:
Padding: A variable-length field making the option length a multiple
of 8, containing as many octets as specified in the Pad Length
field. Typically there is no need of a padding and the field is
NULL.
Just to check: nothing requires the use of minimal-length padding to achieve
the required alignment, and padding of 200+ bytes is permitted by the spec,
albeit silly?
You're right. It looks better to reuse the text in the previous option and we
get:
"
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |Reserved1| Signature Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
. .
. Digital Signature .
. .
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: NDP signature Option
Type: to be assigned by IANA, see Table 1.
Length: 8-bit unsigned integer. The length of the option in units
of 8 octets.
Reserved1: 5-bit unsigned integer. It MUST be set to zero by the
sender and MUST be ignored by the receiver.
Digital Signature Length: 11-bit unsigned integer. The length of
the Digital Signature field in bytes.
Reserved2: 32-bit unsigned integer. It MUST be set to zero by the
sender and MUST be ignored by the receiver.
Digital Signature: A variable-length field containing a digital
signature. The computation of the digital signature depends on
the Crypto-Type which is found in the associated CIPO. For the
values of the Crypto-Type that are defined in this specification,
the signature is computed as detailed in Section 6.2.
Padding: A variable-length field completing the Digital Signature
field to align to the next 8-bytes boundary. It MUST be set to
zero by the sender and MUST be ignored by the receiver.
"
Section 6
This specification enables the 6LR to verify the ownership of the
binding at any time assuming that the "C" flag is set. The
verification prevents other nodes from stealing the address and
trying to attract traffic for that address or use it as their source
address.
nit: I think that the verification cannot be done unilaterally by the 6LR, so
maybe "enables the 6LR to challenge the node to verify its ownership of the
binding at any time" is better.
Applied
A node may use multiple IPv6 addresses at the same time. The node
MAY use the same Crypto-ID, to prove the ownership of multiple IPv6
addresses. The separation of the address and the cryptographic
nit: no comma
Removed
material avoids the constrained device to compute multiple keys for
nit: "avoids the need for"
done
multiple addresses. The registration process allows the node to use
the same Crypto-ID for all of its addresses.
nit(?): We could potentially mention again the ability to use different Crypto-
IDs with a single keypair, though there's not any clear need to do so.
"
A node may use more than one IPv6 address at the same time. The
separation of the address and the cryptographic material avoids
avoids the need for the constrained device to compute multiple keys
for multiple addresses. The 6LN MAY use the same Crypto-ID to prove
the ownership of multiple IPv6 addresses. The 6LN MAY also derive
multiple Crypto-IDs from a same key.
"
Section 6.1
Mostly just for my own elucidation, where is it first specified to put the
address
being registered in the Target Address field of the NS message?
That's a change introduced in RFC 8505. Added the reference.
detrimental to the battery lifetime. Alternatively, the device may
use an always-incrementing value saved in the same stable storage as
the key, so they are lost together, and starting at a best effort
random value, either as Nonce value or as a component to its
computation.
nit: "as the Nonce value".
Done
and the NDPSO containing the signature. The information associated
to a Crypto-ID stored by the 6LR on the first NS exchange where it
appears. The 6LR MUST store the CIPO parameters associated with the
nit: I think there's a verb missing in this sentence ("MUST be"?)
"
The 6LR MUST store the information associated to a Crypto-ID on the
first NS exchange where it appears in a fashion that the CIPO
parameters can be retrieved from the Crypto-ID alone.
"
|------- NS with EARO, CIPO, NonceLN and NDPSO -------->|
(This still includes the Crypto-ID, even if there's not room in the figure to
explicition indicate that, right?)
The Crypto-ID is placed in the ROVR field of the EARO.
There's text after the picture that reminds of this.
More interesting is that the CIPO can be omitted if the same Crypto-ID is used
for more than one registration.
* Upon the first exchange with a 6LR, a 6LN will be challenged to
prove ownership of the Crypto-ID and the Target Address being
How is the "first exchange" tracked? Just whether the 6LR knows about the
registered IPv6 address, or the L2 address, or something else? In particular,
if a
6LR has cached an IP address/ROVR binding, and an attacker tries to join that
6LR with that address/ROVR, what controls whether the 6LR will challenge the
attacker's 6LN? Is it purely at the 6LR's discretion?
Changing the text in section 6 to be more specific on that:
"
The 6LR/6LBR ensures first-come/first-serve by storing the ROVR
associated to the address being registered upon the first
registration and rejecting a registration with a different ROVR
value. A 6LN can claim any address as long as it is the first to
make that claim. After a successful registration, the 6LN becomes
the owner of the registered address and the address is bound to the
ROVR value in the 6LR/6LBR registry.
This specification enables the 6LR to challenge the 6LN to verify its
ownership of the binding by placing a Crypto-ID in the ROVR. The
challenge can happen at any time at the discretion of the 6LR. The
6LR MUST challenge the 6LN when it creates a binding and when a new
registration attempts to change a parameter of the binding that
identifies the 6LN, for instance its Source Link-Layer Address. The
verification protects against a rogue that would steal an address and
attract its traffic, or use it as source address.
"
This specification does not protect the MAC layer and if an attacker can
impersonate the MAC address of the owner then it originate packets, but that
does not change the binding, and the owner will still get its packet, cc the
attacker. If the owner moves it will register elsewhere and the binding will
move. Without the key, the attacker cannot lock the state and it will lose
access to the data.
* The challenge is triggered when the registration for a Source
Link-Layer Address is not verifiable either at the 6LR or the
6LBR. In the latter case, the 6LBR returns a status of
"Validation Requested" in the DAR/DAC exchange, which is echoed by
the 6LR in the NA (EARO) back to the registering node. The
challenge MUST NOT alter a valid registration in the 6LR or the
6LBR.
nit(?): the previous bullet describes a case where the 6LR MUST issue a
challenge; my understanding is that this bullet describes an additional way in
which challenges can occur (i.e., when the 6LBR doesn't know about the
address registration either). Stylistically, it might be more clear to reword
this
as being an "additional case" on top of the previous one, as opposed to the
current wording which tries to be very general about when a challenge can
happen, which is neither a parallel construction to the previous bullet nor
particularly clear about what new information is being conveyed by this bullet.
Moved that text next to the one quoted above in 6. The text is not specific to
the first registration.
"
The challenge can also triggered by the 6LBR, e.g., to enforce a
global policy. In that case, the 6LBR returns a status of
"Validation Requested" in the DAR/DAC exchange, which is echoed by
the 6LR in the NA (EARO) back to the registering node. A valid
registration in the 6LR or the 6LBR MUST NOT be altered until the
challenge is complete.
"
* In order to validate the ownership, the 6LR performs the same
steps as the 6LN and rebuilds the Crypto-ID based on the
parameters in the CIPO. If the rebuilt Crypto-ID matches the
ROVR, the 6LN also verifies the signature contained in the NDPSO
option. If at that point the signature in the NDPSO option can be
verified, then the validation succeeds. Otherwise the validation
fails.
I worry a little bit that we haven't fully specified the entire list of steps
the 6LR
takes to follow the cryptographic chain and validate that the 6LN holds the key
in question and registers the address in question to the Crypto-ID in question.
I
don't have a specific thing in mind that the 6LR might forget, but if we
explicitly state what things are bound to what other things, the 6LR is less
likely
to make a security-relevant mistake.
Another one that I'd rather take separately. Further talks are needed since I
do not see a specific action to take right now,
Section 6.2
Might we want to include the Modifier or the Crypto-ID itself in the signed
data, in addition to the public key, to avoid any potential misbinding?
2. JWK-encoded public key
[just to check: JWK-encoding means that we have an injective map and aren't
subject to some sort of extension attack? Not that such a thing would be easy
to pull off, with a strict registry of Crypto-Types, of course]
Another thing to pull on a separate thread : )
6. The length of the ROVR field in the NS message containing the
Crypto-ID that was sent.
nit: is this really the NS "that was sent" as opposed to the NS under
construction that contains the NDPSO? (This is related to my question up in
Section 6.1.) Tying the initial NS to the followup one requires more state on
the 6LR (though the 6LR probably already had to keep state for the Nonce) and
makes some of the verification steps a bit tougher to implement correctly.
The ROVR size should not change, otherwise it is a different ROVR altogether.
Whanged to
"
The length of the ROVR field containing the Crypto-ID
"
7. 1-byte (in network byte order) Crypto-Type value sent in the CIPO
option.
nit: Is there any byte order with distinct representation from network byte
order, for a 1-byte quantity? ;)
Removed (in network byte order) twice since there's the 6LR side too
* Depending on the Crypto-Type, apply the hash function on this
concatenation.
nit: is this clearer as "Apply the hash function (if any) specified by the
Crypto-
Type to the concatenated data"?
Done
* Depending on the Crypto-Type, sign the hash output with ECDSA (if
curve P-256 is used) or sign the hash with EdDSA (if curve Ed25519
(PureEdDSA)).
nit: this text is not very consistent with the idea of an extensible registry of
Crypto-Types; similar "apply the signature algorithm specified by the Crypto-
Type" language to what I suggested above may be appropriate.
Proposed result:
"
* Apply the hash function (if any) specified by the Crypto-Type to
the concatenated data, e.g., hash the resulting data using SHA-
256.
* Apply the signature algorithm specified by the Crypto-Type, e.g.,
sign the hash output with ECDSA (if curve P-256 is used) or sign
the hash with EdDSA (if curve Ed25519 (PureEdDSA)).
"
The 6LR on receiving the NDPSO and CIPO options first regenerates the
Crypto-ID based on the CIPO option to make sure that the leftmost
bits up to the size of the ROVR match. If and only if the check is
In the vein of my previous questions about where the Crypto-ID appears and
truncation/malleability, this text seems to leave some room for confusion
about how many bits of output are being compared, and compared to what.
I'm unsure what you mean here. Based on my response above, can you please
reopen is needed, with some clarification?
* Depending on the Crypto-Type indicated by the (6LN) in the CIPO,
apply the hash function on this concatenation.
[similar comment as above]
* Verify the signature with the public-key received and the locally
computed values. If the verification succeeds, the 6LR and 6LBR
add the state information about the Crypto-ID, public-key and
Target Address being registered to their database.
This might be a place to reiterate the FCFS nature of address registration,
though it's hardly necessary.
There was a typo there, the public key Is not stored there and is only available to the
6LR. Remove "public-key".
The text becomes
"
* Apply the hash function (if any) specified by the Crypto-Type
indicated by the 6LN in the CIPO to the concatenated data.
* Verify the signature with the public-key in the CIPO and the
locally computed values using the signature algorithm specified by
the Crypto-Type. If the verification succeeds, the 6LR propagates
the information to the 6LBR using a EDAR/EDAC flow. Due to the
first-come/first-serve nature of the registration, if the address
is not registered to the 6LBR, then flow succeeds and both the 6LR
and 6LBR add the state information about the Crypto-ID and Target
Address being registered to their respective abstract database.
"
Section 6.3
In a multihop 6LoWPAN, a 6LBR sends RAs with prefixes downstream and
the 6LR receives and relays them to the nodes. 6LR and 6LBR
communicate using ICMPv6 Duplicate Address Request (DAR) and
Duplicate Address Confirmation (DAC) messages. The DAR and DAC use
the same message format as NS and NA, but have different ICMPv6 type
values.
In AP-ND we extend DAR/DAC messages to carry cryptographically
generated ROVR. In a multihop 6LoWPAN, the node exchanges the
messages shown in Figure 6. The 6LBR must identify who owns an
address (EUI-64) to defend it, if there is an attacker on another
6LR.
This description feels a little vague to me -- I'm interested in knowing how the
6LBR gains confidence that a proof-of-possession was provided to the 6LR, and
how the ROVR gets validated at 6LBR and 6LR when the 6LN in question moves
to a new 6LR. What information remains local to (each) 6LR and what is
communicated between 6LR and 6LBR?
This also relates to the "how trusted are 6LRs?" question I mentioned earlier.
This is really old text that should have been remassaged since.
6.3 is now one page as follows, please met me know if this still misses your
point.
The EDAR contains the registered address and the ROVR. With that the
"
6.3. Multihop Operation
A new 6LN that joins the network auto-configures an address and
performs an initial registration to a neighboring 6LR with an NS
message that carries an Address Registration Option (EARO) [RFC8505].
In a multihop 6LoWPAN, the registration with Crypto-ID is propagated
to 6LBR as shown in Figure 6, which illustrates the registration flow
all the way to a 6LowPAN Backbone Router (6BBR) [BACKBONE-ROUTER].
The 6LR and the 6LBR communicate using ICMPv6 Extended Duplicate
Address Request (EDAR) and Extended Duplicate Address Confirmation
(EDAC) messages [RFC8505] as shown in Figure 6. This specification
extends EDAR/EDAC messages to carry cryptographically generated ROVR.
The assumption is that the 6LR and the 6LBR maintain a security
association, so there is no need to propagate the proof of ownership
to the 6LBR. The 6LBR implicitly trusts that the 6LR performs the
verification when the 6LBR requires it, and if there is no further
exchange from the 6LR to remove the state, that the verification
succeeded.
6LN 6LR 6LBR 6BBR
| | | |
| NS(EARO) | | |
|--------------->| | |
| | Extended DAR | |
| |-------------->| |
| | | |
| | | proxy NS(EARO) |
| | |--------------->|
| | | | NS(DAD)
| | | | ------>
| | | |
| | | | <wait>
| | | |
| | | proxy NA(EARO) |
| | |<---------------|
| | Extended DAC | |
| |<--------------| |
| NA(EARO) | | |
|<---------------| | |
| | | |
Figure 6: (Re-)Registration Flow
"
Section 7
It might be appropriate to talk about how the NonceLR and NonceLN combine
to ensure contributory behavior from both 6LR and 6LN, and that each protects
against a different type of replay attack.
I added text that you suggested earlier in the spec.
Also changed 7.1, see below
Section 7.1
Duplicate Address Detection DoS Attack: Inside the LLN, Duplicate
Addresses are sorted out using the ROVR, which differentiates it
from a movement. DAD coming from the backbone are not forwarded
over the LLN, which provides some protection against DoS attacks
inside the resource-constrained part of the network. Over the
backbone, the EARO option is present in NS/NA messages. This
protects against misinterpreting a movement for a duplication, and
enables the backbone routers to determine which one has the
freshest registration and is thus the best candidate to validate
the registration for the device attached to it. But this
specification does not guarantee that the backbone router claiming
an address over the backbone is not an attacker.
Where do we specify the behavior of the 6LBR to reject EAROs when the 6LBR
is not the one with the freshest registration? Or do I misunderstand the
discussion of "freshest registration"?
This is the backbone router draft based on freshness computation from RFC 8505.
Added references.
Replay Attacks Using Nonces (NonceLR and NonceLN) generated by both
the 6LR and 6LN provides an efficient protection against replay
attacks of challenge response flow. The quality of the protection
still depends on the quality of the Nonce, in particular of a
random generator if they are computed that way.
It's probably worth noting explicitly that we do not require unpredictable
nonces, just non-repeating ones.
All together we get:
"
Replay Attacks Using Nonces (NonceLR and NonceLN) generated by both
the 6LR and 6LN ensure a contributory behavior that provides an
efficient protection against replay attacks of the challenge/
response flow. A nonce should never repeat for a same key. The
protection depends on the quality of the Nonce computation, e.g.,
of a random number generator when used to compute the Nonce.
"
Neighbor Discovery DoS Attack: A rogue node that managed to access
the L2 network may form many addresses and register them using AP-
ND. The perimeter of the attack is all the 6LRs in range of the
attacker. The 6LR MUST protect itself against overflows and
reject excessive registration with a status 2 "Neighbor Cache
Full". This effectively blocks another (honest) 6LN from
registering to the same 6LR, but the 6LN may register to other
6LRs that are in its range but not in that of the rogue.
Are there L2 technologies where L2 media keys are tied to L2 address, so a
rogue node might be rate-limited or given a quota based on L2 address?
It can be done, even with 802.15.4. But sadly that's uncommon in practical
deployments.
Section 7.2
address. This specification frees the device to form its addresses
in any fashion, thereby enabling not only 6LoWPAN compression which
derives IPv6 addresses from Layer-2 addresses but also privacy
addresses.
We noted in Section 1 that the 6lo adaptation layer requires use of L2-address-
based IPv6 address selection, so it's not clear how it would be valid to use
privacy addresses with this specification.
Only the optimal compression requires it. Privacy defeats that compression,
meaning that both L2 and L3 addresses need to be passed in full.
Twisted the text to
"
With this specification the 6LN can freely form its IPv6 address(es)
in any fashion, thereby enabling either 6LoWPAN compression for IPv6
addresses that are derived from Layer-2 addresses, or temporary
addresses, e.g., formed pseudo-randomly and released in relatively
short cycles for privacy reasons [RFC8064][RFC8065], that cannot be
compressed.
"
Section 7.3
We seem to be assuming for these calculations/discussion that the hash used
for calculating the Crypto-ID is a well-behaved cryptographic hash and thus
that random collisions are the only ones possible. It would be worth
mentioning that weaknesses in the hashes associated with a given Crypto-Type
could allow attackers to make more targetted collision attempts.
True, but is there such a problem with SHA-256 and SHA-512?
I'd rather avoid discussing "bad hash" that we do not use, but retiain your
point.
Proposal to change the text to
"
A collision of Registration Ownership Verifiers (ROVR) (i.e., the
Crypto-ID in this specification) is possible, but it is a rare event.
Assuming in the calculations/discussion below that the hash used for
calculating the Crypto-ID is a well-behaved cryptographic hash and
thus that random collisions are the only ones possible, the formula
(birthday paradox) for calculating the probability of a collision is
1 - e^{-k^2/(2n)} where n is the maximum population size (2^64 here,
1.84E19) and k is the actual population (number of nodes, assuming
one Crypto-ID per node).
If the Crypto-ID is 64-bits (the least possible size allowed), the
chance of a collision is 0.01% for network of 66 million nodes.
Moreover, the collision is only relevant when this happens within one
stub network (6LBR). In the case of such a collision, a third party
node would be able to claim the registered address of an another
legitimate node, provided that it wishes to use the same address. To
prevent address disclosure and avoid the chances of collision on both
the RIVR and the address, it is RECOMMENDED that nodes do not derive
the address being registered from the ROVR. "
The formula for calculating the probability of a collision is 1 -
e^{-k^2/(2n)} where n is the maximum population size (2^64 here,
1.84E19) and K is the actual population (number of nodes). If the
nit: minuscule vs. majuscule 'k'/'K'
Fixed
Section 7.4
The signature schemes referenced in this specification comply with
NIST [FIPS186-4] or Crypto Forum Research Group (CFRG) standards
[RFC8032] and offer strong algorithmic security at roughly 128-bit
security level. These signature schemes use elliptic curves that
Do we want to make any forward-looking statement about the expected
strength of future-defined Crypto-Types? ("No" is a fine answer...)
Hum ...
Deferring answer but not too keen in having forward looking stuff that's not
needed to implement in a std track.
My ball in that space is a particularly obscure dark cristal. But I'm open to
proposals.
Section 7.5
The text here is more about cross-algorithm attacks than cross-protocol ones.
It would be great to see some text about cross-protocol attacks added, too
(e.g., prohibiting use of the keypair for anything other than AP-ND).
Agreed. What about:
"
7.5. Cross-Algorithm and Cross-Protocol Attacks
The keypair used in this specification can be self-generated and the
public key does not need to be exchanged, e.g., through certificates,
with a third party before it is used. New keypairs can be formed for
new registration as the node desires. On the other hand, it is safer
to allocate a keypair that is used only for the address protection
and only for one signature scheme. The same private key MUST NOT be
reused with more than one signature scheme in this specification.
The same private key MUST NOT be used for anything other than
computing NDPSO signatures per this specification.
"
Section 7.6
This specification distributes the challenge and its validation at
the edge of the network, between the 6LN and its 6LR. The central
6LBR is offloaded, which avoids DOS attacks targeted at that central
entity. This also saves back and forth exchanges across a
nit: "the central 6LBR is offloaded" reads very oddly, as the offloading is of
work from the 6LBR, but the 6LBR itself remains in place.
What about
"
This protects against DOS attacks targeted at that central 6LBR.
"
The downside is that the 6LBR needs to trust the 6LR for performing
the checking adequately, and the communication between the 6LR and
the 6LBR must be protected to avoid tempering with the result of the
test.
I'd prefer to see some more details about the nature of the required protection
for 6LR/6LBR communications.
Text in the main spec has
"
The assumption is that the 6LR and the 6LBR maintain a security association,
so there is no need to propagate the proof of ownership to the 6LBR.
"
But I'm not aware of people using anything beyond Layer-2 security. The
EDAR/EDAC are unicast ICMPv6 messages; what would be your recommendation to
protect them at L3?
If a 6LR is compromised, it may pretend that it owns any address and
defeat the protection. It may also admit any rogue and let it take
ownership of any address in the network, provided that the 6LR knows
the ROVR field used by the real owner of the address.
nit: this language could probably be tightened up to be more precise about the
hazards.
"
7.6. Compromised 6LR
This specification distributes the challenge and its validation at
the edge of the network, between the 6LN and its 6LR. This protects
against DOS attacks targeted at that central 6LBR. This also saves
back and forth exchanges across a potentially large and constrained
network. The downside is that the 6LBR needs to trust the 6LR for
performing the checking adequately, and the communication between the
6LR and the 6LBR must be protected to avoid tempering with the result
of the test.
If a 6LR is compromised, and provided that it knows the ROVR field
used by the real owner of the address, the 6LR may pretend that the
owner has moved, is now attached to it and has successfully passed the
Crypto-ID validation. The 6LR may then attract and inject traffic at
will on behalf of that address. Similarly, the 6LR may admit any
rogue and let it take ownership of any address in the network for
which it knows the value of ROVR.
"
Section 8.3
New Crypto-Type values providing similar or better security (with
less code) may be defined in the future.
I'm not sure what purpose the "with less code" requirement serves. It seems
to needlessly constrain future actions.
Removed
Section 11
Curve25519 support is a MAY, so I think RFC 7748 belongs as normative;
likewise for RFCs 8032 and 6234.
It's probably better to cite RFC 7696 as BCP 201 directly.
Done
Section B.3
It would be great if the document shepherd could diff the paramters listed here
against [CURVE-REPRESENTATIONS].
Actually we have a co author in common : )
So many thanks!
As I said I published 16 for just the above, because the amount of changes
inline in the mail becomes hard to swallow.
Still please let me know which items require more attention and more changes;
we still have a nimber of open items (3) for which I launched separate threads
All the best
Pascal
