]> Zscaler

yrosomakho@zscaler.com

University of Applied Sciences Bonn-Rhein-Sieg

Germany Hannes.Tschofenig@gmx.net

Transport QUIC quic extended key update forward secrecy This document specifies an Extended Key Update mechanism for the QUIC protocol, building on the foundation of the TLS Extended Key Update. The TLS Extended Key Update specification enhances the TLS protocol by introducing key updates with forward secrecy, eliminating the need to perform a full handshake. This feature is particularly beneficial for maintaining security in scenarios involving long-lived connections. This specification replaces the QUIC Key Update mechanism described in the "Using TLS to Secure QUIC" specification. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the QUIC Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction The QUIC protocol provides a secure, versatile transport for various applications, suitable for long-lived sessions in environments like industrial IoT, telecommunication networks or Virtual Private Networks (VPN), as specified in . The TLS Extended Key Update introduces a mechanism to enhance the security and flexibility of encrypted communication protocols by enabling frequent key updates without requiring a full handshake renegotiation. This approach allows applications to refresh their encryption keys more often, improving forward secrecy and reducing the risk of key compromise over long-lived connections. By separating key updates from the computationally expensive handshake process, the specification provides a lightweight method for maintaining robust encryption in scenarios where connections need to remain secure for extended periods. This new TLS capability is particularly valuable in environments where interruptions to perform a full key exchange would cause significant disruption. Other encrypted communication protocols, such as IPsec and SSH , include mechanisms for re-exchanging keys without interrupting active sessions. The TLS Extended Key Update specification ensures that even in the face of potential key compromise, sensitive data remains protected due to frequent key rotation and the use of forward secrecy. This specification builds on concepts from and applies them to the QUIC protocol context. It thereby replaces the QUIC Key Update mechanism described in .

Conventions and Definitions 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 when, and only when, they appear in all capitals, as shown here. Readers are assumed to be familiar with .

Extended Key Update Negotiation QUIC peers negotiate Extended Key Update through the TLS handshake process, as outlined in . Extended Key Update MUST NOT be used unless both QUIC peers include the TLS flags extension in the handshake and set the "Extended_Key_Update" flag. Once Extended Key Update has been succesfully negotiated, QUIC peers MUST only use the Extended Key Update process defined in this document. The standard QUIC Key Update mechanism from MUST NOT be used for the duration of the session, as both Key Update and Extended Key Update use the Key Phase bit to signal the use of updated keys. The Key Phase bit is initially set to 0 and toggled to indicate a key update following the succesful post-handshake exchange of Extended Key Update messsages.

Extended Key Update Messages Either party MAY initiate the Extended Key Update process by sending an ExtendedKeyUpdateRequest TLS handshake message in a QUIC CRYPTO frame. This message MUST NOT be sent before the QUIC handshake is confirmed, as described in , or before previous Extended Key Update process is complete. If a QUIC endpoints receives an ExtendedKeyUpdateRequest message before the QUIC handshake is complete or during ongoing prior Extended Key Update, it MUST terminate the connection with an error of type 0x010a, equivalent to TLS unexpected_message alert as specified in . Upon receiving an ExtendedKeyUpdateRequest, the recipient MUST respond with an ExtendedKeyUpdateResponse TLS handshake message within a QUIC CRYPTO frame. If a QUIC endpoint receives an unexpected ExtendedKeyUpdateResponse message from its peer, it MUST treat this as a TLS protocol error and terminate the connection. Specifications of the ExtendedKeyUpdateRequest and ExtendedKeyUpdateResponse messages are provided in . Any mismatch between the negotiated NamedGroup during the initial handshake and the group used in the Extended Key Update message, or an incorrect length of the encapsulated key MUST result in connection termination with error of type 0x012f, equivalend to TLS illegal_parameter alert. If the Extended Key Update initiator receives a retry or rejected status in the ExtendedKeyUpdateResponse message, it MAY terminate the connection with error of type 0x01TBD, equivalent to TLS extended_key_update_required alert.

Updating the Traffic Secrets After sending an ExtendedKeyUpdateResponse with accepted status, the responder derives new packet protection traffic secrets. The responder MUST continue using the previous secrets until it has received a packet with the Key Phase bit flipped and has successfully unprotected it using the new keys. After receiving and succesfully processing an ExtendedKeyUpdateResponse with accepted status, the initiator derives new packet protection traffic secrets, flips the Key Phase bit for new packets, and uses the new write secret to protect them. The initiator MUST retain the old read secret until it has received a packet with a flipped Key Phase bit from the responder and succesfully unprotected it using the new read secret. Both endpoints SHOULD retain old read secrets for some time after unprotecting a packet encrypted with the new keys. Discarding old secret too early may cause delayed packets to be discarded, which the peer may interpreted as packet loss, potentially impacting performance. shows this interaction graphically.

Extended Key Update Process in QUIC. <-------- [ packet using old key and prior Key Phase ] ... [ExtendedKeyUpdateRequest] --------> <-------- [ExtendedKeyUpdateResponse] [ packet using new key and updated Key Phase ] --------> <-------- [ packet using new key and updated Key Phase ] ... ]]>

QUIC endpoints MUST NOT send NewKeyUpdate TLS handshake messages, defined in , and instead rely on the use of the Key Phase bit. Endpoints MUST treat the receipt of a TLS NewKeyUpdate message as a connection error of type 0x010a. QUIC endpoints that have agreed to the Extended Key Update process MUST NOT change the Key Phase bit without a succesful exchange of Extended Key Update TLS messages. Receiving a packet with the Key Phase bit changed without a success Extended Key Update exchange MUST be treated as a connection error of type KEY_UPDATE_ERROR (0x0e). The design of the key derivation function for computing the next generation of secrets corresponds to the one described in with the exception of the use of a different label. = HKDF-Expand-Label(sk, "quic eku", secret_, Hash.length) ]]> The corresponding key and IV are derived from the new secret as defined in . The header protection key is not updated.

Security Considerations This specification describes an update to the key schedule of QUIC. Therefore, implementations MUST ensure that peers adhere strictly to the process described in this document. Packets with higher packet numbers MUST NOT be protected using an older generation of secrets, as this could compromise key synchronization and security. As key exchange may be computationally intensive, responders SHOULD consider rate-limiting Extended Key Exchange requests. This can be done by responding with retry status as outlined in and terminating connections for initiators that violate the back-off timer. This approach helps prevent excessive load on endpoints and mitigates the risk of denial-of-service attacks.

IANA Considerations This document has no IANA actions.

References Normative References This document defines the core of the QUIC transport protocol. QUIC provides applications with flow-controlled streams for structured communication, low-latency connection establishment, and network path migration. QUIC includes security measures that ensure confidentiality, integrity, and availability in a range of deployment circumstances. Accompanying documents describe the integration of TLS for key negotiation, loss detection, and an exemplary congestion control algorithm. Siemens Münster Univ. of Applied Sciences Nokia Siemens Zscaler The Transport Layer Security (TLS) 1.3 specification provides forward secrecy by utilizing an ephemeral key exchange during the initial handshake. Forward secrecy ensures that even if an attacker later obtains a party's long-term private key, past encrypted sessions cannot be decrypted. This protects against adversaries who record encrypted conversations in the hope of decrypting them later. TLS 1.3 also includes a Key Update mechanism, allowing cryptographic keys to be refreshed during an ongoing session. However, this update does not establish new forward-secret key material. While this is generally not an issue for short-lived sessions, it can pose a security risk for long-lived connections, such as those in industrial IoT or telecommunication networks, where an attacker could compromise application traffic secrets after the initial handshake. Earlier versions of TLS supported session renegotiation, a mechanism that allowed peers to establish new cryptographic parameters within an existing session. This included the ability to update the originally used long-term keys (certificates) with renewed credentials. However, due to security vulnerabilities, the renegotiation mechanism was modified via RFC 5746 and later removed entirely in TLS 1.3, leaving a gap in TLS's ability to refresh cryptographic material securely. This specification introduces an extended key update mechanism that supports forward secrecy, forcing attackers to continuously exfiltrate key material throughout the session to decrypt the entire conversation. This document describes how Transport Layer Security (TLS) is used to secure QUIC. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Dell Technologies A number of extensions are proposed in the TLS working group that carry no interesting information except the 1-bit indication that a certain optional feature is supported. Such extensions take 4 octets each. This document defines a flags extension that can provide such indications at an average marginal cost of 1 bit each. More precisely, it provides as many flag extensions as needed at 4 + the order of the last set bit divided by 8. Informative References This document describes how to proxy IP packets in HTTP. This protocol is similar to UDP proxying in HTTP but allows transmitting arbitrary IP packets. More specifically, this document defines a protocol that allows an HTTP client to create an IP tunnel through an HTTP server that acts as an IP proxy. This document updates RFC 9298. This document describes version 2 of the Internet Key Exchange (IKE) protocol. IKE is a component of IPsec used for performing mutual authentication and establishing and maintaining Security Associations (SAs). This document obsoletes RFC 5996, and includes all of the errata for it. It advances IKEv2 to be an Internet Standard. The Secure Shell (SSH) is a protocol for secure remote login and other secure network services over an insecure network. This document describes the SSH transport layer protocol, which typically runs on top of TCP/IP. The protocol can be used as a basis for a number of secure network services. It provides strong encryption, server authentication, and integrity protection. It may also provide compression. Key exchange method, public key algorithm, symmetric encryption algorithm, message authentication algorithm, and hash algorithm are all negotiated. This document also describes the Diffie-Hellman key exchange method and the minimal set of algorithms that are needed to implement the SSH transport layer protocol. [STANDARDS-TRACK]

Acknowledgments We would like to thank Martin Thomson and Sean Turner for their early review of this design and their invaluable feedback.