 1/draftietfsfcproofoftransit01.txt 20190311 03:13:54.246893083 0700
+++ 2/draftietfsfcproofoftransit02.txt 20190311 03:13:54.298894334 0700
@@ 1,32 +1,34 @@
Network Working Group F. Brockners
InternetDraft S. Bhandari
Intended status: Experimental S. Dara
Expires: April 4, 2019 C. Pignataro
+Intended status: Experimental Cisco
+Expires: September 12, 2019 S. Dara
+ Seconize
+ C. Pignataro
Cisco
J. Leddy
Comcast
S. Youell
JPMC
D. Mozes
T. Mizrahi
 Marvell
+ Huawei Network.IO Innovation Lab
A. Aguado
Universidad Politecnica de Madrid
D. Lopez
Telefonica I+D
 October 1, 2018
+ March 11, 2019
Proof of Transit
 draftietfsfcproofoftransit01
+ draftietfsfcproofoftransit02
Abstract
Several technologies such as Traffic Engineering (TE), Service
Function Chaining (SFC), and policy based routing are used to steer
traffic through a specific, userdefined path. This document defines
mechanisms to securely prove that traffic transited said defined
path. These mechanisms allow to securely verify whether, within a
given path, all packets traversed all the nodes that they are
supposed to visit.
@@ 38,86 +40,86 @@
InternetDrafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as InternetDrafts. The list of current Internet
Drafts is at http://datatracker.ietf.org/drafts/current/.
InternetDrafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use InternetDrafts as reference
material or to cite them other than as "work in progress."
 This InternetDraft will expire on April 4, 2019.
+
+ This InternetDraft will expire on September 12, 2019.
Copyright Notice
 Copyright (c) 2018 IETF Trust and the persons identified as the
+ Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/licenseinfo) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Proof of Transit . . . . . . . . . . . . . . . . . . . . . . 5
 3.1. Basic Idea . . . . . . . . . . . . . . . . . . . . . . . 5
 3.2. Solution Approach . . . . . . . . . . . . . . . . . . . . 6
+ 3.1. Basic Idea . . . . . . . . . . . . . . . . . . . . . . . 6
+ 3.2. Solution Approach . . . . . . . . . . . . . . . . . . . . 7
3.2.1. Setup . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2.2. In Transit . . . . . . . . . . . . . . . . . . . . . 7
 3.2.3. Verification . . . . . . . . . . . . . . . . . . . . 7
 3.3. Illustrative Example . . . . . . . . . . . . . . . . . . 7
 3.3.1. Basic Version . . . . . . . . . . . . . . . . . . . . 7
+ 3.2.3. Verification . . . . . . . . . . . . . . . . . . . . 8
+ 3.3. Illustrative Example . . . . . . . . . . . . . . . . . . 8
+ 3.3.1. Baseline . . . . . . . . . . . . . . . . . . . . . . 8
3.3.1.1. Secret Shares . . . . . . . . . . . . . . . . . . 8
 3.3.1.2. Lagrange Polynomials . . . . . . . . . . . . . . 8
 3.3.1.3. LPC Computation . . . . . . . . . . . . . . . . . 8
+ 3.3.1.2. Lagrange Polynomials . . . . . . . . . . . . . . 9
+ 3.3.1.3. LPC Computation . . . . . . . . . . . . . . . . . 9
3.3.1.4. Reconstruction . . . . . . . . . . . . . . . . . 9
 3.3.1.5. Verification . . . . . . . . . . . . . . . . . . 9
 3.3.2. Enhanced Version . . . . . . . . . . . . . . . . . . 9
 3.3.2.1. Random Polynomial . . . . . . . . . . . . . . . . 9
+ 3.3.1.5. Verification . . . . . . . . . . . . . . . . . . 10
+ 3.3.2. Complete Solution . . . . . . . . . . . . . . . . . . 10
+ 3.3.2.1. Random Polynomial . . . . . . . . . . . . . . . . 10
3.3.2.2. Reconstruction . . . . . . . . . . . . . . . . . 10
 3.3.2.3. Verification . . . . . . . . . . . . . . . . . . 10
 3.3.3. Final Version . . . . . . . . . . . . . . . . . . . . 11
 3.4. Operational Aspects . . . . . . . . . . . . . . . . . . . 11
+ 3.3.2.3. Verification . . . . . . . . . . . . . . . . . . 11
+ 3.3.3. Solution Deployment Considerations . . . . . . . . . 11
+ 3.4. Operational Aspects . . . . . . . . . . . . . . . . . . . 12
3.5. Ordered POT (OPOT) . . . . . . . . . . . . . . . . . . . 12
 3.5.1. Nested Encryption . . . . . . . . . . . . . . . . . . 12
 3.5.2. Symmetric Masking Between Nodes . . . . . . . . . . . 12
4. Sizing the Data for Proof of Transit . . . . . . . . . . . . 13
5. Node Configuration . . . . . . . . . . . . . . . . . . . . . 14
 5.1. Procedure . . . . . . . . . . . . . . . . . . . . . . . . 14
+ 5.1. Procedure . . . . . . . . . . . . . . . . . . . . . . . . 15
5.2. YANG Model . . . . . . . . . . . . . . . . . . . . . . . 15
+
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
7. Manageability Considerations . . . . . . . . . . . . . . . . 18
 8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
 8.1. Proof of Transit . . . . . . . . . . . . . . . . . . . . 18
 8.2. Cryptanalysis . . . . . . . . . . . . . . . . . . . . . . 19
+ 8. Security Considerations . . . . . . . . . . . . . . . . . . . 19
+ 8.1. Proof of Transit . . . . . . . . . . . . . . . . . . . . 19
+ 8.2. Cryptanalysis . . . . . . . . . . . . . . . . . . . . . . 20
8.3. AntiReplay . . . . . . . . . . . . . . . . . . . . . . . 20
 8.4. AntiPreplay . . . . . . . . . . . . . . . . . . . . . . 20
 8.5. AntiTampering . . . . . . . . . . . . . . . . . . . . . 21
+ 8.4. AntiPreplay . . . . . . . . . . . . . . . . . . . . . . 21
+ 8.5. Tampering . . . . . . . . . . . . . . . . . . . . . . . . 21
8.6. Recycling . . . . . . . . . . . . . . . . . . . . . . . . 21
 8.7. Redundant Nodes and Failover . . . . . . . . . . . . . . 21
 8.8. Controller Operation . . . . . . . . . . . . . . . . . . 21
+ 8.7. Redundant Nodes and Failover . . . . . . . . . . . . . . 22
+ 8.8. Controller Operation . . . . . . . . . . . . . . . . . . 22
8.9. Verification Scope . . . . . . . . . . . . . . . . . . . 22
 8.9.1. Node Ordering . . . . . . . . . . . . . . . . . . . . 22
 8.9.2. Stealth Nodes . . . . . . . . . . . . . . . . . . . . 22
+ 8.9.1. Node Ordering . . . . . . . . . . . . . . . . . . . . 23
+ 8.9.2. Stealth Nodes . . . . . . . . . . . . . . . . . . . . 23
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 23
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
10.1. Normative References . . . . . . . . . . . . . . . . . . 23
 10.2. Informative References . . . . . . . . . . . . . . . . . 23
 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
+ 10.2. Informative References . . . . . . . . . . . . . . . . . 24
+ Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
Several deployments use Traffic Engineering, policy routing, Segment
Routing (SR), and Service Function Chaining (SFC) [RFC7665] to steer
packets through a specific set of nodes. In certain cases,
regulatory obligations or a compliance policy require operators to
prove that all packets that are supposed to follow a specific path
are indeed being forwarded across and exact set of predetermined
nodes.
@@ 149,30 +151,29 @@
indeed traversed a specific set of service functions or nodes allows
operators to evolve from the above described indirect methods of
proving that packets visit a predetermined set of nodes.
The solution approach presented in this document is based on a small
portion of operational data added to every packet. This "insitu"
operational data is also referred to as "proof of transit data", or
POT data. The POT data is updated at every required node and is used
to verify whether a packet traversed all required nodes. A
particular set of nodes "to be verified" is either described by a set
 of secret keys, or a set of shares of a single secret. Nodes on the
 path retrieve their individual keys or shares of a key (using for
 e.g., Shamir's Secret Sharing scheme) from a central controller. The
 complete key set is only known to the controller and a verifier node,
 which is typically the ultimate node on a path that performs
 verification. Each node in the path uses its secret or share of the
 secret to update the POT data of the packets as the packets pass
 through the node. When the verifier receives a packet, it uses its
 key(s) along with data found in the packet to validate whether the
 packet traversed the path correctly.
+ of shares of a single secret. Nodes on the path retrieve their
+ individual shares of the secret using Shamir's Secret Sharing scheme
+ from a central controller. The complete secret set is only known to
+ the controller and a verifier node, which is typically the ultimate
+ node on a path that performs verification. Each node in the path
+ uses its share of the secret to update the POT data of the packets as
+ the packets pass through the node. When the verifier receives a
+ packet, it uses its key along with data found in the packet to
+ validate whether the packet traversed the path correctly.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Abbreviations used in this document:
HMAC: Hash based Message Authentication Code. For example,
@@ 187,175 +188,205 @@
MTU: Maximum Transmit Unit
NFV: Network Function Virtualization
NSH: Network Service Header
POT: Proof of Transit
POTprofile: Proof of Transit Profile that has the necessary data
for nodes to participate in proof of transit
 RND: Random Bits generated per packet. Packet fields that
 donot change during the traversal are given as input to
+ RND: Random Bits generated per packet. Packet fields that do
+ not change during the traversal are given as input to
HMAC256 algorithm. A minimum of 32 bits (left most) need
to be used from the output if RND is used to verify the
packet integrity. This is a standard recommendation by
NIST.
SEQ_NO: Sequence number initialized to a predefined constant.
This is used in concatenation with RND bits to mitigate
different attacks discussed later.
SFC: Service Function Chain
+ SSSS: Shamir's Secret Sharing Scheme
+
SR: Segment Routing
3. Proof of Transit
This section discusses methods and algorithms to provide for a "proof
of transit" for packets traversing a specific path. A path which is
to be verified consists of a set of nodes. Transit of the data
packets through those nodes is to be proven. Besides the nodes, the
setup also includes a Controller that creates secrets and secrets
shares and configures the nodes for POT operations.
The methods how traffic is identified and associated to a specific
path is outside the scope of this document. Identification could be
done using a filter (e.g., 5tuple classifier), or an identifier
which is already present in the packet (e.g., path or service
identifier, NSH Service Path Identifier (SPI), flowlabel, etc.)
+ The POT information is encapsulated in packets as an IOAM Proof Of
+ Transit Option. The details and format of the encapsulation and the
+ POT Option format are specified in [ID.ietfippmioamdata].
+
The solution approach is detailed in two steps. Initially the
concept of the approach is explained. This concept is then further
refined to make it operationally feasible.
3.1. Basic Idea
The method relies on adding POT data to all packets that traverse a
path. The added POT data allows a verifying node (egress node) to
check whether a packet traversed the identified set of nodes on a
path correctly or not. Security mechanisms are natively built into
 the generation of the POT data to protect against misuse (i.e.
 configuration mistakes, malicious administrators playing tricks with
 routing, capturing, spoofing and replaying packets). The mechanism
 for POT leverages "Shamir's Secret Sharing" scheme [SSS].
+ the generation of the POT data to protect against misuse (e.g.,
+ configuration mistakes). The mechanism for POT leverages "Shamir's
+ Secret Sharing" scheme [SSS].
Shamir's secret sharing base idea: A polynomial (represented by its
 coefficients) is chosen as a secret by the controller. A polynomial
 represents a curve. A set of welldefined points on the curve are
 needed to construct the polynomial. Each point of the polynomial is
 called "share" of the secret. A single secret is associated with a
 particular set of nodes, which typically represent the path, to be
 verified. Shares of the single secret (i.e., points on the curve)
 are securely distributed from a Controller to the network nodes.
 Nodes use their respective share to update a cumulative value in the
 POT data of each packet. Only a verifying node has access to the
 complete secret. The verifying node validates the correctness of the
 received POT data by reconstructing the curve.
+ coefficients) of degree k is chosen as a secret by the controller. A
+ polynomial represents a curve. A set of k+1 points on the curve
+ define the polynomial and are thus needed to (re)construct the
+ polynomial. Each of these k+1 points of the polynomial is called a
+ "share" of the secret. A single secret is associated with a
+ particular set of k+1 nodes, which typically represent the path to be
+ verified. k+1 shares of the single secret (i.e., k+1 points on the
+ curve) are securely distributed from a Controller to the network
+ nodes. Nodes use their respective share to update a cumulative value
+ in the POT data of each packet. Only a verifying node has access to
+ the complete secret. The verifying node validates the correctness of
+ the received POT data by reconstructing the curve.
 The polynomial cannot be constructed if any of the points are missed
 or tampered. Per Shamir's Secret Sharing Scheme, any lesser points
 means one or more nodes are missed. Details of the precise
+ The polynomial cannot be reconstructed if any of the points are
+ missed or tampered. Per Shamir's Secret Sharing Scheme, any lesser
+ points means one or more nodes are missed. Details of the precise
configuration needed for achieving security are discussed further
below.
While applicable in theory, a vanilla approach based on Shamir's
 secret sharing could be easily attacked. If the same polynomial is
 reused for every packet for a path a passive attacker could reuse the
 value. As a consequence, one could consider creating a different
 polynomial per packet. Such an approach would be operationally
 complex. It would be complex to configure and recycle so many curves
 and their respective points for each node. Rather than using a
 single polynomial, two polynomials are used for the solution
 approach: A secret polynomial which is kept constant, and a per
 packet polynomial which is public. Operations are performed on the
 sum of those two polynomials  creating a third polynomial which is
 secret and per packet.
+ Secret Sharing Scheme could be easily attacked. If the same
+ polynomial is reused for every packet for a path a passive attacker
+ could reuse the value. As a consequence, one could consider creating
+ a different polynomial per packet. Such an approach would be
+ operationally complex. It would be complex to configure and recycle
+ so many curves and their respective points for each node. Rather
+ than using a single polynomial, two polynomials are used for the
+ solution approach: A secret polynomial as described above which is
+ kept constant, and a perpacket polynomial which is public and
+ generated by the ingress node (the first node along the path).
+ Operations are performed on the sum of those two polynomials 
+ creating a third polynomial which is secret and per packet.
3.2. Solution Approach
Solution approach: The overall algorithm uses two polynomials: POLY1
 and POLY2. POLY1 is secret and constant. Each node gets a point
 on POLY1 at setuptime and keeps it secret. POLY2 is public,
 random and per packet. Each node generates a point on POLY2 each
 time a packet crosses it. Each node then calculates (point on POLY1
 + point on POLY2) to get a (point on POLY3) and passes it to
 verifier by adding it to each packet. The verifier constructs POLY3
 from the points given by all the nodes and cross checks whether
 POLY3 = POLY1 + POLY2. Only the verifier knows POLY1. The
 solution leverages finite field arithmetic in a field of size "prime
+ and POLY2. POLY1 is secret and constant. A different POLY1 is
+ used for each path, and its value is known to the controller and to
+ the verifier of the respective path. Each node gets a point on
+ POLY1 at setuptime and keeps it secret. POLY2 is public, random
+ and per packet. Each node generates a point on POLY2 each time a
+ packet crosses it. Each node then calculates (point on POLY1 +
+ point on POLY2) to get a (point on POLY3) and passes it to verifier
+ by adding it to each packet. The verifier constructs POLY3 from the
+ points given by all the nodes and cross checks whether POLY3 =
+ POLY1 + POLY2. Only the verifier knows POLY1.
+
+ The solution leverages finite field arithmetic in a field of size
+ "prime number", i.e. all operations are performed "modulo prime
number".
 Detailed algorithms are discussed next. A simple example is
 discussed in Section 3.3.
+ Detailed algorithms are discussed next. A simple example that
+ describes how the algorithms work is discussed in Section 3.3.
+
+ The algorithms themselves do not constrain the ranges of possible
+ values for the different parameters and coefficients used. A
+ deployment of the algorithms will always need to define appropriate
+ ranges. Please refer to the YANG model in Section 5.2 for details on
+ the units and ranges of possible values of the different parameters
+ and coefficients.
3.2.1. Setup
A controller generates a first polynomial (POLY1) of degree k and
 k+1 points on the polynomial. The constant coefficient of POLY1 is
 considered the SECRET. The nonconstant coefficients are used to
 generate the Lagrange Polynomial Constants (LPC). Each of the k
 nodes (including verifier) are assigned a point on the polynomial
 i.e., shares of the SECRET. The verifier is configured with the
 SECRET. The Controller also generates coefficients (except the
 constant coefficient, called "RND", which is changed on a per packet
 basis) of a second polynomial POLY2 of the same degree. Each node
 is configured with the LPC of POLY2. Note that POLY2 is public.
+ k+1 points on the polynomial, corresponding to the k+1 nodes along
+ the path. The constant coefficient of POLY1 is considered the
+ SECRET, which is per the definition of the SSSS algorithm [SSS]. The
+ nonconstant coefficients are used to generate the Lagrange
+ Polynomial Constants (LPC). Each of the k+1 nodes (including
+ verifier) are assigned a point on the polynomial i.e., shares of the
+ SECRET. The verifier is configured with the SECRET. The Controller
+ also generates coefficients (except the constant coefficient, called
+ "RND", which is changed on a per packet basis) of a second polynomial
+ POLY2 of the same degree. Each node is configured with the LPC of
+ POLY2. Note that POLY2 is public.
3.2.2. In Transit
For each packet, the ingress node generates a random number (RND).
It is considered as the constant coefficient for POLY2. A
cumulative value (CML) is initialized to 0. Both RND, CML are
carried as within the packet POT data. As the packet visits each
node, the RND is retrieved from the packet and the respective share
of POLY2 is calculated. Each node calculates (Share(POLY1) +
 Share(POLY2)) and CML is updated with this sum. This step is
 performed by each node until the packet completes the path. The
 verifier also performs the step with its respective share.
+ Share(POLY2)) and CML is updated with this sum, specifically each
+ node performs
+
+ CML = CML+(((Share(POLY1)+ Share(POLY2)) * LPC) mod Prime, with
+ "LPC" being the Lagrange Polynomial Constant and "Prime" being the
+ prime number which defines the finite field arithmetic that all
+ operations are done over. Please also refer to Section 3.3.2 below
+ for further details how the operations are performed.
+
+ This step is performed by each node until the packet completes the
+ path. The verifier also performs the step with its respective share.
3.2.3. Verification
The verifier cross checks whether CML = SECRET + RND. If this
matches then the packet traversed the specified set of nodes in the
path. This is due to the additive homomorphic property of Shamir's
Secret Sharing scheme.
3.3. Illustrative Example
This section shows a simple example to illustrate step by step the
 approach described above.
+ approach described above. The example assumes a network with 3
+ nodes. The last node that packets traverse also serves as the
+ verifier. A Controller communicates the required parameters to the
+ individual nodes.
3.3.1. Basic Version
+3.3.1. Baseline
 Assumption: It is to be verified whether packets passed through 3
+ Assumption: It is to be verified whether packets passed through the 3
nodes. A polynomial of degree 2 is chosen for verification.
Choices: Prime = 53. POLY1(x) = (3x^2 + 3x + 10) mod 53. The
secret to be reconstructed is the constant coefficient of POLY1,
i.e., SECRET=10. It is important to note that all operations are
 done over a finite field (i.e., modulo prime).
+ done over a finite field (i.e., modulo Prime = 53).
3.3.1.1. Secret Shares
The shares of the secret are the points on POLY1 chosen for the 3
nodes. For example, let x0=2, x1=4, x2=5.
POLY1(2) = 28 => (x0, y0) = (2, 28)
POLY1(4) = 17 => (x1, y1) = (4, 17)

POLY1(5) = 47 => (x2, y2) = (5, 47)
The three points above are the points on the curve which are
 considered the shares of the secret. They are assigned to three
 nodes respectively and are kept secret.
+ considered the shares of the secret. They are assigned by the
+ Controller to three nodes respectively and are kept secret.
3.3.1.2. Lagrange Polynomials
Lagrange basis polynomials (or Lagrange polynomials) are used for
polynomial interpolation. For a given set of points on the curve
Lagrange polynomials (as defined below) are used to reconstruct the
curve and thus reconstruct the complete secret.
l0(x) = (((xx1) / (x0x1)) * ((xx2)/x0x2))) mod 53 =
(((x4) / (24)) * ((x5)/25))) mod 53 =
@@ 365,27 +396,28 @@
(5 + 7x/2  (1/2)x^2) mod 53
l2(x) = (((xx0) / (x2x0)) * ((xx1)/x2x1))) mod 53 =
(8/3  2 + (1/3)x^2) mod 53
3.3.1.3. LPC Computation
Since x0=2, x1=4, x2=5 are chosen points. Given that computations
are done over a finite arithmetic field ("modulo a prime number"),
the Lagrange basis polynomial constants are computed modulo 53. The
 Lagrange Polynomial Constant (LPC) would be 10/3 , 5 , 8/3.
+ Lagrange Polynomial Constant (LPC) would be 10/3 , 5 , 8/3.LPC are
+ computed by the Controller and communicated to the individual nodes.
 LPC(x0) = (10/3) mod 53 = 21
+ LPC(l0) = (10/3) mod 53 = 21
 LPC(x1) = (5) mod 53 = 48
+ LPC(l1) = (5) mod 53 = 48
 LPC(x2) = (8/3) mod 53 = 38
+ LPC(l2) = (8/3) mod 53 = 38
For a general way to compute the modular multiplicative inverse, see
e.g., the Euclidean algorithm.
3.3.1.4. Reconstruction
Reconstruction of the polynomial is welldefined as
POLY1(x) = l0(x) * y0 + l1(x) * y1 + l2(x) * y2
@@ 384,57 +416,57 @@
e.g., the Euclidean algorithm.
3.3.1.4. Reconstruction
Reconstruction of the polynomial is welldefined as
POLY1(x) = l0(x) * y0 + l1(x) * y1 + l2(x) * y2
Subsequently, the SECRET, which is the constant coefficient of
POLY1(x) can be computed as below

SECRET = (y0*LPC(l0)+y1*LPC(l1)+y2*LPC(l2)) mod 53
The secret can be easily reconstructed using the yvalues and the
LPC:
SECRET = (y0*LPC(l0) + y1*LPC(l1) + y2*LPC(l2)) mod 53 = mod (28 * 21
+ 17 * 48 + 47 * 38) mod 53 = 3190 mod 53 = 10
One observes that the secret reconstruction can easily be performed
 cumulatively hop by hop. CML represents the cumulative value. It is
 the POT data in the packet that is updated at each hop with the
 node's respective (yi*LPC(i)), where i is their respective value.
+ cumulatively hop by hop, i.e. by every node. CML represents the
+ cumulative value. It is the POT data in the packet that is updated
+ at each hop with the node's respective (yi*LPC(i)), where i is their
+ respective value.
3.3.1.5. Verification
Upon completion of the path, the resulting CML is retrieved by the
 verifier from the packet POT data. Recall that verifier is
+ verifier from the packet POT data. Recall that the verifier is
preconfigured with the original SECRET. It is cross checked with the
CML by the verifier. Subsequent actions based on the verification
failing or succeeding could be taken as per the configured policies.
3.3.2. Enhanced Version
+3.3.2. Complete Solution
 As observed previously, the vanilla algorithm that involves a single
 secret polynomial is not secure. Therefore, the solution is further
 enhanced with usage of a random second polynomial chosen per packet.
+ As observed previously, the baseline algorithm that involves a single
+ secret polynomial is not secure. The complete solution leverages a
+ random second polynomial, which is chosen per packet.
3.3.2.1. Random Polynomial
Let the second polynomial POLY2 be (RND + 7x + 10 x^2). RND is a
random number and is generated for each packet. Note that POLY2 is
public and need not be kept secret. The nodes can be preconfigured
with the nonconstant coefficients (for example, 7 and 10 in this
case could be configured through the Controller on each node). So
 precisely only RND value changes per packet and is public and the
 rest of the nonconstant coefficients of POLY2 kept secret.
+ precisely only the RND value changes per packet and is public and the
+ rest of the nonconstant coefficients of POLY2 is kept secret.
3.3.2.2. Reconstruction
Recall that each node is preconfigured with their respective
Share(POLY1). Each node calculates its respective Share(POLY2)
using the RND value retrieved from the packet. The CML
reconstruction is enhanced as below. At every node, CML is updated
as
CML = CML+(((Share(POLY1)+ Share(POLY2)) * LPC) mod Prime
@@ 470,27 +501,27 @@
As shown in the above example, for final verification, the verifier
compares:
VERIFY = (SECRET + RND) mod Prime, with Prime = 53 here
VERIFY = (RND1 + RND2) mod Prime = ( 10 + 45 ) mod 53 = 2
Since VERIFY = CML the packet is proven to have gone through nodes 1,
2, and 3.
3.3.3. Final Version
+3.3.3. Solution Deployment Considerations
 The enhanced version of the protocol is still prone to replay and
 preplay attacks. An attacker could reuse the POT metadata for
 bypassing the verification. So additional measures using packet
 integrity checks (HMAC) and sequence numbers (SEQ_NO) are discussed
 later "Security Considerations" section.
+ The "complete solution" described above in Section 3.3.2 could still
+ be prone to replay or preplay attacks. An attacker could e.g. reuse
+ the POT metadata for bypassing the verification. These threats can
+ be mitigated by appropriate parameterization of the algorithm.
+ Please refer to Section 8 for details.
3.4. Operational Aspects
To operationalize this scheme, a central controller is used to
generate the necessary polynomials, the secret share per node, the
prime number, etc. and distributing the data to the nodes
participating in proof of transit. The identified node that performs
the verification is provided with the verification key. The
information provided from the Controller to each of the nodes
participating in proof of transit is referred to as a proof of
@@ 519,67 +550,36 @@
before, the public portion is only the constant coefficient RND
value, the preevaluated portion for each node should be kept
secret as well.
3. To provide flexibility on the size of the cumulative and random
numbers carried in the POT data a field to indicate this is
shared and interpreted at the nodes.
3.5. Ordered POT (OPOT)
 In certain scenarios preserving the order of the nodes traversed by
 the packet may be needed. Two alternatives, one based on "nested
 encryption", and another based on "symmetric masking between nodes"
 are described here for preserving the order

3.5.1. Nested Encryption

 1. The controller provisions all the nodes with their respective
 secret keys.

 2. The controller provisions the verifier with all the secret keys
 of the nodes.

 3. For each packet, the ingress node generates a random number RND
 and encrypts it with its secret key to generate CML value

 4. Each subsequent node on the path encrypts CML with their
 respective secret key and passes it along

 5. The verifier is also provisioned with the expected sequence of
 nodes in order to verify the order

 6. The verifier receives the CML, RND values, reencrypts the RND
 with keys in the same order as expected sequence to verify.

 With this nested encryption approach it is possible to retain the
 order in which the nodes are traversed, at the cost of:

 1. Standard AES encryption would need 128 bits of RND, CML. This
 results in a 256 bits of additional overhead is added per packet

 2. In hardware platforms that do not support native encryption
 capabilities like (AESNI). This approach would have
 considerable impact on the computational latency

3.5.2. Symmetric Masking Between Nodes
+ POT as discussed in this document so far only verifies that a defined
+ set of nodes have been traversed by a packet. The order in which
+ nodes where traversed is not verified. "Ordered Proof of Transit
+ (OPOT)" addresses the need of deployments, that require to verify the
+ order in which nodes were traversed. OPOT extends the POT scheme
+ with symmetric masking between the nodes.
 1. The controller provisions all the nodes with (or asks them to
 agree on) a couple of secrets, that we will refer as masks, one
 for the connection from the upstream node(s), another for the
 connection to the downstream node(s). For obvious reasons, the
 ingress and egress (verifier) nodes only receive one, for
 downstream and upstream, respectively.
+ 1. For each path the controller provisions all the nodes with (or
+ asks them to agree on) two secrets per node, that we will refer
+ to as masks, one for the connection from the upstream node(s),
+ another for the connection to the downstream node(s). For
+ obvious reasons, the ingress and egress (verifier) nodes only
+ receive one, for downstream and upstream, respectively.
2. Any two contiguous nodes in the OPOT stream share the mask for
the connection between them, in the shape of symmetric keys.

Masks can be refreshed as perpolicy, defined at each hop or
globally by the controller.
3. Each mask has the same size in bits as the length assigned to CML
plus RND, as described in the above sections.
4. Whenever a packet is received at an intermediate node, the
CML+RND sequence is deciphered (by XORing, though other ciphering
schemas MAY be possible) with the upstream mask before applying
the procedures described in Section 3.3.2.
@@ 642,42 +642,45 @@
   4*10^9  
 100 Gbps  32  2^32 = approx.  22 seconds 
   4*10^9  
+++++
Table assumes 64 octet packets
Table 1: Proof of transit data sizing
If the symmetric masking method for ordered POT is used
 (Section 3.5.2), the masks used between nodes adjacent in the path
 MUST have a length equal to the sum of the ones of RND and CML.
+ (Section 3.5), the masks used between nodes adjacent in the path MUST
+ have a length equal to the sum of the ones of RND and CML.
5. Node Configuration
A POT system consists of a number of nodes that participate in POT
and a Controller, which serves as a control and configuration entity.
The Controller is to create the required parameters (polynomials,
 prime number, etc.) and communicate those to the nodes. The sum of
 all parameters for a specific node is referred to as "POTprofile".
 This document does not define a specific protocol to be used between
 Controller and nodes. It only defines the procedures and the
 associated YANG data model.
+ prime number, etc.) and communicate the associated values (i.e. prime
+ number, secretshare, LPC, etc.) to the nodes. The sum of all
+ parameters for a specific node is referred to as "POTprofile". For
+ details see the YANG model in Section 5.2.This document does not
+ define a specific protocol to be used between Controller and nodes.
+ It only defines the procedures and the associated YANG data model.
5.1. Procedure
The Controller creates new POTprofiles at a constant rate and
communicates the POTprofile to the nodes. The controller labels a
POTprofile "even" or "odd" and the Controller cycles between "even"
 and "odd" labeled profiles. The rate at which the POTprofiles are
 communicated to the nodes is configurable and is more frequent than
 the speed at which a POTprofile is "used up" (see table above).
+ and "odd" labeled profiles. This means that the parameters for the
+ algorithms are continuously refreshed. Please refer to Section 4 for
+ choosing an appropriate refresh rate: The rate at which the POT
+ profiles are communicated to the nodes is configurable and MUST be
+ more frequent than the speed at which a POTprofile is "used up".
Once the POTprofile has been successfully communicated to all nodes
(e.g., all NETCONF transactions completed, in case NETCONF is used as
a protocol), the controller sends an "enable POTprofile" request to
the ingress node.
All nodes maintain two POTprofiles (an even and an odd POTprofile):
One POTprofile is currently active and in use; one profile is
standby and about to get used. A flag in the packet is indicating
whether the odd or even POTprofile is to be used by a node. This is
to ensure that during profile change the service is not disrupted.
@@ 839,22 +841,31 @@
IANA considerations will be added in a future version of this
document.
7. Manageability Considerations
Manageability considerations will be addressed in a later version of
this document.
8. Security Considerations
 Different security requirements achieved by the solution approach are
 discussed here.
+ POT is a mechanism that is used for verifying the path through which
+ a packet was forwarded. The security considerations of IOAM in
+ general are discussed in [ID.ietfippmioamdata]. Specifically, it
+ is assumed that POT is used in a confined network domain, and
+ therefore the potential threats that POT is intended to mitigate
+ should be viewed accordingly. POT prevents spoofing and tampering;
+ an attacker cannot maliciously create a bogus POT or modify a
+ legitimate one. Furthermore, a legitimate node that takes part in
+ the POT protocol cannot masquerade as another node along the path.
+ These considerations are discussed in detail in the rest of this
+ section.
8.1. Proof of Transit
Proof of correctness and security of the solution approach is per
Shamir's Secret Sharing Scheme [SSS]. Cryptographically speaking it
achieves informationtheoretic security i.e., it cannot be broken by
an attacker even with unlimited computing power. As long as the
below conditions are met it is impossible for an attacker to bypass
one or multiple nodes without getting caught.
@@ 870,22 +881,22 @@
and nonconstant coefficient of POLY2 are secret
An attacker bypassing a few nodes will miss adding a respective point
on POLY1 to corresponding point on POLY2 , thus the verifier cannot
construct POLY3 for cross verification.
Also it is highly recommended that different polynomials should be
used as POLY1 across different paths, traffic profiles or service
chains.
 If symmetric masking is used to assure OPOT (Section 3.5.2), the
 nodes need to keep two additional secrets: the upstream and upstream
+ If symmetric masking is used to assure OPOT (Section 3.5), the nodes
+ need to keep two additional secrets: the downstream and upstream
masks, that have to be managed under the same conditions as the
secrets mentioned above. And it is equally recommended to employ a
different set of mask pairs across different paths, traffic profiles
or service chains.
8.2. Cryptanalysis
A passive attacker could try to harvest the POT data (i.e., CML, RND
values) in order to determine the configured secrets. Subsequently
two types of differential analysis for guessing the secrets could be
@@ 899,27 +910,30 @@
(i.e. RND, CMLbefore, CMLafter). The application of symmetric
masking for OPOT makes internode analysis less feasible.
o InterPackets: A passive attacker could observe CML values across
packets (i.e., values of PKT1 and subsequent PKT2), in order to
predict the secrets. Differential analysis across packets could
be mitigated using a good PRNG for generating RND. Note that if
constant coefficient is a sequence number than CML values become
quite predictable and the scheme would be broken. If symmetric
masking is used for OPOT, interpacket analysis could be applied
 to guess mask values, what requires a proper refresh rate for
+ to guess mask values, which requires a proper refresh rate for
masks, at least as high as the one used for LPCs.
8.3. AntiReplay
A passive attacker could reuse a set of older RND and the
 intermediate CML values to bypass certain nodes in later packets.
+ intermediate CML values. Thus, an attacker can attack an old
+ (replayed) RND and CML with a new packet in order to bypass some of
+ the nodes along the path.
+
Such attacks could be avoided by carefully choosing POLY2 as a
(SEQ_NO + RND). For example, if 64 bits are being used for POLY2
then first 16 bits could be a sequence number SEQ_NO and next 48 bits
could be a random number.
Subsequently, the verifier could use the SEQ_NO bits to run classic
antireplay techniques like sliding window used in IPSEC. The
verifier could buffer up to 2^16 packets as a sliding window.
Packets arriving with a higher SEQ_NO than current buffer could be
flagged legitimate. Packets arriving with a lower SEQ_NO than
@@ 953,41 +967,41 @@
to generate RND. It is recommended to use a minimum of 32 bits.
o The verifier regenerates the HMAC from the packet fields and
compares with RND. To ensure the POT data is in fact that of the
packet.
If an HMAC is used, an active attacker lacks the knowledge of the
preshared key, and thus cannot launch preplay attacks.
The solution discussed in this memo does not currently mitigate
 prereplay attacks. A mitigation mechanism may be included in future
+ preplay attacks. A mitigation mechanism may be included in future
versions of the solution.
8.5. AntiTampering
+8.5. Tampering
An active attacker could not insert any arbitrary value for CML.
This would subsequently fail the reconstruction of the POLY3. Also
an attacker could not update the CML with a previously observed
value. This could subsequently be detected by using timestamps
within the RND value as discussed above.
8.6. Recycling
The solution approach is flexible for recycling long term secrets
like POLY1. All the nodes could be periodically updated with shares
of new SECRET as best practice. The table above could be consulted
for refresh cycles (see Section 4).
 If symmetric masking is used for OPOT (Section 3.5.2), mask values
 must be periodically updated as well, at least as frequently as the
 other secrets are.
+ If symmetric masking is used for OPOT (Section 3.5), mask values must
+ be periodically updated as well, at least as frequently as the other
+ secrets are.
8.7. Redundant Nodes and Failover
A "node" or "service" in terms of POT can be implemented by one or
multiple physical entities. In case of multiple physical entities
(e.g., for loadbalancing, or business continuity situations 
consider for example a set of firewalls), all physical entities which
are implementing the same POT node are given that same share of the
secret. This makes multiple physical entities represent the same POT
node from an algorithm perspective.
@@ 1004,21 +1018,21 @@
configuration and thereafter at regular intervals at which the
operator chooses to switch to a new set of secrets. In case 64 bits
are used for the data fields "CML" and "RND" which are carried within
the data packet, the regular intervals are expected to be quite long
(e.g., at 100 Gbps, a profile would only be used up after 3100 years)
 see Section 4 above, thus even a "headless" operation without a
Controller can be considered feasible. In such a case, the
Controller would only be used for the initial configuration of the
POTprofiles.
 If OPOT (Section 3.5.2) is applied using symmetric masking, the
+ If OPOT (Section 3.5) is applied using symmetric masking, the
Controller will be required to perform a a periodic refresh of the
mask pairs. The use of OPOT SHOULD be configurable as part of the
required level of assurance through the Controller management
interface.
8.9. Verification Scope
The POT solution defined in this document verifies that a datapacket
traversed or transited a specific set of nodes. From an algorithm
perspective, a "node" is an abstract entity. It could be represented
@@ 1054,29 +1068,36 @@
The authors would like to thank Eric Vyncke, Nalini Elkins, Srihari
Raghavan, Ranganathan T S, Karthik Babu Harichandra Babu, Akshaya
Nadahalli, Erik Nordmark, and Andrew Yourtchenko for the comments and
advice.
10. References
10.1. Normative References
+ [ID.ietfippmioamdata]
+ Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
+ Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
+ P., Chang, R., daniel.bernier@bell.ca, d., and J. Lemon,
+ "Data Fields for Insitu OAM", draftietfippmioam
+ data04 (work in progress), October 2018.
+
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
 RFC2119, March 1997, .
+ Requirement Levels", BCP 14, RFC 2119,
+ DOI 10.17487/RFC2119, March 1997, .
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
 Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/
 RFC7665, October 2015, .
+ Chaining (SFC) Architecture", RFC 7665,
+ DOI 10.17487/RFC7665, October 2015, .
[SSS] "Shamir's Secret Sharing", .
10.2. Informative References
[ID.ietfanimaautonomiccontrolplane]
Eckert, T., Behringer, M., and S. Bjarnason, "An Autonomic
Control Plane (ACP)", draftietfanimaautonomiccontrol
plane18 (work in progress), August 2018.
@@ 1083,36 +1104,35 @@
Authors' Addresses
Frank Brockners
Cisco Systems, Inc.
Hansaallee 249, 3rd Floor
DUESSELDORF, NORDRHEINWESTFALEN 40549
Germany
Email: fbrockne@cisco.com
+
Shwetha Bhandari
Cisco Systems, Inc.
Cessna Business Park, Sarjapura Marathalli Outer Ring Road
Bangalore, KARNATAKA 560 087
India
Email: shwethab@cisco.com
Sashank Dara
 Cisco Systems, Inc.
 Cessna Business Park, Sarjapura Marathalli Outer Ring Road
 BANGALORE, Bangalore, KARNATAKA 560 087
+ Seconize
+ BANGALORE, Bangalore, KARNATAKA
INDIA
 Email: sadara@cisco.com

+ Email: sashank@seconize.co
Carlos Pignataro
Cisco Systems, Inc.
720011 Kit Creek Road
Research Triangle Park, NC 27709
United States
Email: cpignata@cisco.com
John Leddy
Comcast
@@ 1123,35 +1143,33 @@
JP Morgan Chase
25 Bank Street
London E14 5JP
United Kingdom
Email: stephen.youell@jpmorgan.com
David Mozes
Email: mosesster@gmail.com
+
Tal Mizrahi
 Marvell
 6 Hamada St.
 Yokneam 20692
+ Huawei Network.IO Innovation Lab
Israel
 Email: talmi@marvell.com
+ Email: tal.mizrahi.phd@gmail.com
Alejandro Aguado
Universidad Politecnica de Madrid
Campus Montegancedo, Boadilla del Monte
Madrid 28660
Spain
Phone: +34 910 673 086
Email: a.aguadom@fi.upm.es

Diego R. Lopez
Telefonica I+D
Editor Jose Manuel Lara, 9 (1B)
Seville 41013
Spain
Phone: +34 913 129 041
Email: diego.r.lopez@telefonica.com