Internet Engineering Task Force N. Elkins Internet-Draft Inside Products, Inc. Intended status: Standards Track M. Ackermann Expires: 26 December 2023 BCBS Michigan A. Deshpande NITK Surathkal/Google T. Pecorella University of Florence A. Rashid Politecnico di Bari 24 June 2023 IPv6 Performance and Diagnostic Metrics Version 2 (PDMv2) Destination Option draft-ietf-ippm-encrypted-pdmv2-04 Abstract RFC8250 describes an optional Destination Option (DO) header embedded in each packet to provide sequence numbers and timing information as a basis for measurements. As this data is sent in clear-text, this may create an opportunity for malicious actors to get information for subsequent attacks. This document defines PDMv2 which has a lightweight handshake (registration procedure) and encryption to secure this data. Additional performance metrics which may be of use are also defined. About This Document This note is to be removed before publishing as an RFC. The latest revision of this draft can be found at https://ameyand.github.io/PDMv2/draft-elkins-ippm-encrypted- pdmv2.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-ietf-ippm-encrypted-pdmv2/. Discussion of this document takes place on the IP Performance Measurement Working Group mailing list (mailto:ippm@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/ippm/. Subscribe at https://www.ietf.org/mailman/listinfo/ippm/. Source for this draft and an issue tracker can be found at https://github.com/ameyand/PDMv2. Elkins, et al. Expires 26 December 2023 [Page 1] Internet-Draft draft-ietf-ippm-encrypted-pdmv2 June 2023 Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts 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 Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 26 December 2023. Copyright Notice Copyright (c) 2023 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 (https://trustee.ietf.org/ license-info) 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Current Performance and Diagnostic Metrics (PDM) . . . . 3 1.2. PDMv2 Introduction . . . . . . . . . . . . . . . . . . . 3 2. Conventions used in this document . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . . . 4 4.1. Cryptographic Phase . . . . . . . . . . . . . . . . . . . 5 4.2. Client - Server Negotiation . . . . . . . . . . . . . . . 5 5. Security Goals . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. Security Goals for Confidentiality . . . . . . . . . . . 6 5.2. Security Goals for Integrity . . . . . . . . . . . . . . 6 5.3. Security Goals for Authentication . . . . . . . . . . . . 7 5.4. Cryptographic Algorithm . . . . . . . . . . . . . . . . . 7 6. PDMv2 Destination Options . . . . . . . . . . . . . . . . . . 7 6.1. Destinations Option Header . . . . . . . . . . . . . . . 7 Elkins, et al. Expires 26 December 2023 [Page 2] Internet-Draft draft-ietf-ippm-encrypted-pdmv2 June 2023 6.2. Metrics information in PDMv2 . . . . . . . . . . . . . . 8 6.3. PDMv2 Layout . . . . . . . . . . . . . . . . . . . . . . 9 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7.1. Resource exhaustion attacks . . . . . . . . . . . . . . . 12 7.2. Effects of a Client or Server Compromise . . . . . . . . 13 8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 13 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 11.1. Normative References . . . . . . . . . . . . . . . . . . 14 11.2. Informative References . . . . . . . . . . . . . . . . . 14 Appendix A. Sample Implementation of Registration . . . . . . . 14 A.1. Overall summary . . . . . . . . . . . . . . . . . . . . . 15 A.2. High level flow . . . . . . . . . . . . . . . . . . . . . 15 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 15 Appendix C. Open Issues . . . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 1. Introduction 1.1. Current Performance and Diagnostic Metrics (PDM) The current PDM is an IPv6 Destination Options header which provides information based on the metrics like Round-trip delay and Server delay. This information helps to measure the Quality of Service (QoS) and to assist in diagnostics. However, there are potential risks involved transmitting PDM data during a diagnostics session. PDM metrics can help an attacker understand about the type of machine and its processing capabilities. Inferring from the PDM data, the attack can launch a timing attack. For example, if a cryptographic protocol is used, a timing attack may be launched against the keying material to obtain the secret. Along with this, PDM does not provide integrity. It is possible for a Man-In-The-Middle (MITM) node to modify PDM headers leading to incorrect conclusions. For example, during the debugging process using PDM header, it can mislead the person showing there are no unusual server delays. 1.2. PDMv2 Introduction PDMv2 adds confidentiality, integrity and authentication to PDM. Elkins, et al. Expires 26 December 2023 [Page 3] Internet-Draft draft-ietf-ippm-encrypted-pdmv2 June 2023 2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 3. Terminology * Client: An endpoint node which initiates a session with a listening port and sends PDM data. Creates cryptographic keys in collaboration with the Server. * Server: An endpoint node which has a listening port and sends PDM data. Creates cryptographic keys in collaboration with the Client. Note: a client may act as a server (have listening ports). * Symmetric Key (K): A uniformly random bitstring as an input to the encryption algorithm, known only to Clients and Servers. Used to establish a secure communication. * Public and Private Keys: A pair of keys that is used in asymmetric cryptography. If one is used for encryption, the other is used for decryption. Private Keys are kept hidden by the source of the key pair generator, but Public Key is known to everyone. pkX (Public Key) and skX (Private Key). Where X can be, any client or any server. * Pre-shared Key (PSK): A symmetric key. Uniformly random bitstring, shared between any Client or any Server or a key shared between an entity that forms client-server relationship. This could happen through an out-of band mechanism: e.g., a physical meeting or use of another protocol. * Session Key: A temporary key which acts as a symmetric key for the whole session. 4. Protocol Flow The protocol will proceed in 2 steps. Step 1: Creation of cryptographic secrets between Server and Client. Step 2: PDM data flow between Client and Server. Elkins, et al. Expires 26 December 2023 [Page 4] Internet-Draft draft-ietf-ippm-encrypted-pdmv2 June 2023 These steps may be in the same session or in separate sessions. That is, the cryptographic secrets may be created beforehand and used in the PDM data flow at the time of the "real" data session. After-the-fact (or real-time) data analysis of PDM flow may occur by network diagnosticians or network devices. The definition of how this is done is out of scope for this document. 4.1. Cryptographic Phase 4.2. Client - Server Negotiation The two entities exchange a set of data to ensure the respective identities. They use HPKE KEM to negotiate a "SharedSecret". Each Client and Server derive a "SessionTemporaryKey" by using HPKE KDF, using the following inputs: * The "SharedSecret". * The 5-tuple (SrcIP, SrcPort, DstIP, DstPort, Protocol) of the communication. * A Key Rotation Index (Kri). The Kri SHOULD be initialized to zero. The Server and Client initialize (separately) a pseudo-random non- repeating sequence between 1 and 2^15-1. How to generate this sequence is beyond the scope of this document, and does not affect the rest of the specification. When the sequence is used fully, or earlier if appropriate, the sender signals the other party that a key change is necessary. This is achieved by flipping the "F bit" and resetting the PRSEQ. The receiver increments the Kri of the sender, and derives another SessionTemporaryKey to be used for decryption. It shall be stressed that the two SessionTemporaryKeys used in the communication are never the same, as the 5-tuple is reversed for the Server and Client. Moreover, the time evolution of the respective Kri can be different. As a consequence, each entity must maintain a table with (at least) the following informations: * Flow 5-tuple, Own Kri, Other Kri Elkins, et al. Expires 26 December 2023 [Page 5] Internet-Draft draft-ietf-ippm-encrypted-pdmv2 June 2023 An implementation might optimize this further by caching the OwnSessionTemporaryKey (used in Encryption) and OtherSessionTemporaryKey (used in Decryption). 5. Security Goals As discussed in the introduction, PDM data can represent a serious data leakage in presence of a malicious actor. In particular, the sequence numbers included in the PDM header allows correlating the traffic flows, and the timing data can highlight the operational limits of a server to a malicious actor. Moreover, forging PDM headers can lead to unnecessary, unwanted, or dangerous operational choices, e.g., to restore an apparently degraded Quality of Service (QoS). Due to this, it is important that the confidentiality and integrity of the PDM headers is maintained. PDM headers can be encrypted and authenticated using the methods discussed in Section 5.4, thus ensuring confidentiality and integrity. However, if PDM is used in a scenario where the integrity and confidentiality is already ensured by other means, they can be transmitted without encryption or authentication. This includes, but is not limited to, the following cases: a) PDM is used over an already encrypted medium (For example VPN tunnels). b) PDM is used in a link-local scenario. c) PDM is used in a corporate network where there are security measures strong enough to consider the presence of a malicious actor a negligible risk. 5.1. Security Goals for Confidentiality PDM data must be kept confidential between the intended parties, which includes (but is not limited to) the two entities exchanging PDM data, and any legitimate party with the proper rights to access such data. 5.2. Security Goals for Integrity PDM data must not be forged or modified by a malicious entity. In other terms, a malicious entity must not be able to generate a valid PDM header impersonating an endpoint, and must not be able to modify a valid PDM header. Elkins, et al. Expires 26 December 2023 [Page 6] Internet-Draft draft-ietf-ippm-encrypted-pdmv2 June 2023 5.3. Security Goals for Authentication An unauthorized party must not be able to send PDM data and must not be able to authorize another entity to do so. The protocol to define this will be defined in a subsequent document. Alternatively, if authentication is done via any of the following, this requirement may be seen to be met. a) PDM is used over an already authenticated medium (For example, TLS session). b) PDM is used in a link-local scenario. c) PDM is used in a corporate network where security measures are strong enough to consider the presence of a malicious actor a negligible risk. 5.4. Cryptographic Algorithm Symmetric key cryptography has performance benefits over asymmetric cryptography; asymmetric cryptography is better for key management. Encryption schemes that unite both have been specified in [RFC1421], and have been participating practically since the early days of public-key cryptography. The basic mechanism is to encrypt the symmetric key with the public key by joining both yields. Hybrid public-key encryption schemes (HPKE) [RFC9180] used a different approach that generates the symmetric key and its encapsulation with the public key of the receiver. Our choice is to use the HPKE framework that incorporates key encapsulation mechanism (KEM), key derivation function (KDF) and authenticated encryption with associated data (AEAD). These multiple schemes are more robust and significantly efficient than the traditional schemes and thus lead to our choice of this framework. 6. PDMv2 Destination Options 6.1. Destinations Option Header The IPv6 Destination Options extension header [RFC8200] is used to carry optional information that needs to be examined only by a packet's destination node(s). The Destination Options header is identified by a Next Header value of 60 in the immediately preceding header and is defined in RFC 8200 [RFC8200]. The IPv6 PDMv2 destination option is implemented as an IPv6 Option carried in the Destination Options header. Elkins, et al. Expires 26 December 2023 [Page 7] Internet-Draft draft-ietf-ippm-encrypted-pdmv2 June 2023 6.2. Metrics information in PDMv2 The IPv6 PDMv2 destination option contains the following base fields: SCALEDTLR: Scale for Delta Time Last Received SCALEDTLS: Scale for Delta Time Last Sent GLOBALPTR: Global Pointer PSNTP: Packet Sequence Number This Packet PSNLR: Packet Sequence Number Last Received DELTATLR: Delta Time Last Received DELTATLS: Delta Time Last Sent PDMv2 adds a new metric to the existing PDM [RFC8250] called the Global Pointer. The existing PDM fields are identified with respect to the identifying information called a "5-tuple". The 5-tuple consists of: SADDR: IP address of the sender SPORT: Port for the sender DADDR: IP address of the destination DPORT: Port for the destination PROTC: Upper-layer protocol (TCP, UDP, ICMP, etc.) Unlike PDM fields, Global Pointer (GLOBALPTR) field in PDMv2 is defined for the SADDR type. Following are the SADDR address types considered: a) Link-Local b) Global Unicast The Global Pointer is treated as a common entity over all the 5-tuples with the same SADDR type. It is initialised to the value 1 and increments for every packet sent. Global Pointer provides a measure of the amount of IPv6 traffic sent by the PDMv2 node. Elkins, et al. Expires 26 December 2023 [Page 8] Internet-Draft draft-ietf-ippm-encrypted-pdmv2 June 2023 When the SADDR type is Link-Local, the PDMv2 node sends Global Pointer defined for Link-Local addresses, and when the SADDR type is Global Unicast, it sends the one defined for Global Unicast addresses. 6.3. PDMv2 Layout PDMv2 has two different header formats corresponding to whether the metric contents are encrypted or unencrypted. The difference between the two types of headers is determined from the Options Length value. Following is the representation of the unencrypted PDMv2 header: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Option Length | Vrsn | Reserved Bits | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Random Number |f| ScaleDTLR | ScaleDTLS | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Global Pointer | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PSN This Packet | PSN Last Received | |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Delta Time Last Received | Delta Time Last Sent | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Following is the representation of the encrypted PDMv2 header: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Option Length | Vrsn | Reserved Bits | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Random Number |f| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ : | Encrypted PDM Data : : (30 bytes) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option Type 0x0F 8-bit unsigned integer. The Option Type is adopted from RFC 8250 [RFC8250]. Option Length Elkins, et al. Expires 26 December 2023 [Page 9] Internet-Draft draft-ietf-ippm-encrypted-pdmv2 June 2023 0x12: Unencrypted PDM 0x22: Encrypted PDM 8-bit unsigned integer. Length of the option, in octets, excluding the Option Type and Option Length fields. The options length is used for differentiating PDM [RFC8250], unencrypted PDMv2 and encrypted PDMv2. Version Number 0x2 4-bit unsigned number. Reserved Bits 12-bits. Reserved bits for future use. They are initialised to 0 for PDMv2. Random Number 15-bit unsigned number. This is a random number with as much entropy as desired by the implementation. The level of entropy should be clearly specified to the user. Flag Bit 1-bit field. The flag bit indicates that the sender has used a new _SessionTemporaryKey_ and the receiver should increment the Kri of the sender and derive the same new _SessionTemporaryKey_. Scale Delta Time Last Received (SCALEDTLR) 8-bit unsigned number. This is the scaling value for the Delta Time Last Sent (DELTATLS) field. Scale Delta Time Last Sent (SCALEDTLS) 8-bit unsigned number. Elkins, et al. Expires 26 December 2023 [Page 10] Internet-Draft draft-ietf-ippm-encrypted-pdmv2 June 2023 This is the scaling value for the Delta Time Last Sent (DELTATLS) field. Global Pointer 32-bit unsigned number. Global Pointer is initialized to 1 for the different source address types and incremented monotonically for each packet with the corresponding source address type. This field stores the Global Pointer type corresponding to the SADDR type of the packet. Packet Sequence Number This Packet (PSNTP) 16-bit unsigned number. This field is initialized at a random number and is incremented monotonically for each packet of the 5-tuple. Packet Sequence Number Last Received (PSNLR) 16-bit unsigned number. This field is the PSNTP of the last received packet on the 5-tuple. Delta Time Last Received (DELTATLR) 16-bit unsigned integer. The value is set according to the scale in SCALEDTLR. Delta Time Last Received = (send time packet n - receive time packet (n - 1)) Delta Time Last Sent (DELTATLS) 16-bit unsigned integer. The value is set according to the scale in SCALEDTLS. Delta Time Last Sent = (receive time packet n - send time packet (n - 1)) Elkins, et al. Expires 26 December 2023 [Page 11] Internet-Draft draft-ietf-ippm-encrypted-pdmv2 June 2023 7. Security Considerations PDMv2 DOH can be used by an attacker to gather information about a victim (passive attack) or to force the victim to modify its operational parameters to comply with forged data (active attacks). In order to mitigate these, it is important that the PDMv2 DOH is subject to: 1) Confidentiality and 2) Integrity with respect to an attacker. As outlined in Section 4.1, the Client and the Server share a "SharedSecret", which can be used to decrypt the data. A leakage of this secret can lead to a confidentiality and integrity violation. It is advised to avoid using the same "SharedSecret" in different Clients and Server pairs. Assuming that the "SharedSecret" is not compromised, an attacker will not be able to recover it even in the case of a brute-force attack to the _SessionTemporaryKey_. Moreover, the key rotation of the _SessionTemporaryKey_ ensures a forward secrecy. 7.1. Resource exhaustion attacks The present document does not covers online decryption. Hence, it is not foreseen a computation resource exhaustion attack due to bogus PDMv2 header insertion by an attacker. However, logging any incoming PDMv2 header might lead to a storage resource exhaustion. Hence, it is suggested to not log PDMv2 headers incoming from an unknown party. In other terms, PDMv2 logging should be enabled only for sessions that have PDMv2 enabled. The simple fact that a packet contains a PDMv2 header should not result in a logging event. An attacker can still inject bogus packets with PDMv2 headers for a valid PDMv2-enabled session. This, to a lesser extent, can cause an increase in resource utilization. However, these bogus headers will be found at decryption time. To further mitigate this attack, it is advised to log the PDMv2 headers only for packets with expected Epoch and/or PSNTP. Elkins, et al. Expires 26 December 2023 [Page 12] Internet-Draft draft-ietf-ippm-encrypted-pdmv2 June 2023 The definition of "expected" is dependent on the traffic flow type and the network characteristics (e.g., bandwidth, delay, loss, reordering, etc.), and it is left to the implementation. Replay attacks, performed by inserting a valid PDMv2 header sniffed from an existing session in a bogus packet, should not be considered a threat, as the offline decryption and analysis should be able to find and eliminate out-of-order data. Hence, we do not consider this as a threat. 7.2. Effects of a Client or Server Compromise If a Client or a Server is compromised, i.e., an attacker takes control of the device, the attacker can leverage the knowledge of the "SharedSecret" to encrypt (and, potentially, decrypt) the PDMv2 data. To mitigate this event, we suggest: * The "SharedSecret" should not be shared by different Clients or Servers, unless all of them are trusted, or unless the risk of a "SecretKey" violation has been evaluated and considered acceptable. * The "SharedSecret" could be stored in a secure, tamper-resistant memory area capable of deriving the _SessionTemporaryKey_ without disclosing the "SharedSecret". Note that the second point is only necessary for cases where device tampering is very likely, and the security of the system has to be guaranteed. 8. Privacy Considerations PDMv2 greatly improves the privacy aspects of PDM by providing encryption. 9. IANA Considerations Option Type to be assigned by IANA [RFC2780]. 10. Contributors The authors wish to thank NITK Surathkal for their support and assistance in coding and review. In particular Dr. Mohit Tahiliani and Abhishek Kumar (now with Google). Thanks also to Priyanka Sinha for her comments. Thanks to the India Internet Engineering Society (iiesoc.in), in particular Dhruv Dhody, for providing the funding for servers needed for protocol development. Elkins, et al. Expires 26 December 2023 [Page 13] Internet-Draft draft-ietf-ippm-encrypted-pdmv2 June 2023 11. References 11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For Values In the Internet Protocol and Related Headers", BCP 37, RFC 2780, DOI 10.17487/RFC2780, March 2000, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 2017, . [RFC8250] Elkins, N., Hamilton, R., and M. Ackermann, "IPv6 Performance and Diagnostic Metrics (PDM) Destination Option", RFC 8250, DOI 10.17487/RFC8250, September 2017, . 11.2. Informative References [RFC1421] Linn, J., "Privacy Enhancement for Internet Electronic Mail: Part I: Message Encryption and Authentication Procedures", RFC 1421, DOI 10.17487/RFC1421, February 1993, . [RFC9180] Barnes, R., Bhargavan, K., Lipp, B., and C. Wood, "Hybrid Public Key Encryption", RFC 9180, DOI 10.17487/RFC9180, February 2022, . Appendix A. Sample Implementation of Registration Elkins, et al. Expires 26 December 2023 [Page 14] Internet-Draft draft-ietf-ippm-encrypted-pdmv2 June 2023 A.1. Overall summary In the Registration phase, the objective is to generate a shared secret that will be used in encryption and decryption during the Data Transfer phase. We have adopted a Primary-Secondary architecture to represent the clients and servers (see Section 4.1.1). The primary server and primary client perform Key Encapsulation Mechanism (KEM) [RFC9180] to generate a primary shared secret. The primary server shares this secret with secondary servers, whereas the primary client performs Key Derivation Function (KDF) [RFC9180] to share client- specific secrets to corresponding secondary clients. During the Data Transfer phase, the secondary servers generate the client-specific secrets on the arrival of the first packet from the secondary client. A.2. High level flow The following steps describe the protocol flow: 1. Client initiates a request to the Server. The request contains a list of available ciphersuites for KEM, KDF, and AEAD. 2. Server responds to the Client with one of the available ciphersuites and shares its public key. 3. Client generates a secret and its encapsulation. The Client sends the encapsulation and a salt to the Server. The salt is required during KDF in the Data Transfer phase. 4. Server generates the secret with the help of the encapsulation and responds with a status message. Appendix B. Change Log Note to RFC Editor: if this document does not obsolete an existing RFC, please remove this appendix before publication as an RFC. Appendix C. Open Issues Note to RFC Editor: please remove this appendix before publication as an RFC. Authors' Addresses Nalini Elkins Inside Products, Inc. Email: nalini.elkins@insidethestack.com Elkins, et al. Expires 26 December 2023 [Page 15] Internet-Draft draft-ietf-ippm-encrypted-pdmv2 June 2023 Michael Ackermann BCBS Michigan Email: mackermann@bcbsm.com Ameya Deshpande NITK Surathkal/Google Email: ameyanrd@gmail.com Tommaso Pecorella University of Florence Email: tommaso.pecorella@unifi.it Adnan Rashid Politecnico di Bari Email: adnan.rashid@poliba.it Elkins, et al. Expires 26 December 2023 [Page 16]