How RFC 9242 and RFC 9370 Resist Quantum Computing Threats
IKEv2 VPNs based on RFC 9242 and RFC 9370 resist quantum attacks today by
safeguarding key exchange material.
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The
RFC 9242 standard,
Intermediate Key Exchange in the
Internet Key Exchange Protocol 2 (IKEv2)
, enables IKEv2 to transfer large
amounts of data in the IKEv2 Security Association (SA) establishment to support multiple
PQC key exchanges with larger key sizes. The
RFC
9370 standard,
Multiple Key Exchanges in the Internet Key Exchange
Protocol 2 (IKEv2)
, allows multiple key exchanges to take place while
computing a shared secret during the SA setup.
Together, these two RFC standards give IKEv2 the ability to create hybrid keys
using both classic and PQC key exchange mechanisms (KEMs) to mitigate a quantum attack
using
Shor’s algorithm. The new PQCs are based on different
mathematical technology that are not vulnerable to known classical or quantum attacks,
and these include:
The RFC 9370 standard allows an additional seven key exchange rounds, and these
can be classic or PQC KEMs, such as ML-KEM, BIKE, HQC, Classic McEliese, and others, in
addition to the IKEv2 default key exchange for a total of eight rounds.
To break the hybrid key, all KEM technologies used to create the encryption key
must fall to a vulnerability and be compromised. For example, to create a hybrid key
that is resistant to both today’s known vulnerabilities and future quantum computer (QC)
threats, best practice recommends using both classic and one or more PQC KEMs that use
different mathematical technologies.
Default KEM Round: Diffie-Hellman (DH) Group 21
Additional Key Exchange Round 1: ML-KEM-768 (CRYSTALS-Kyber-786)
Additional Key Exchange Round 2: BIKE-L3
In the previous example, classic DH Group 21 provides protection for today's
prequantum attacks. Adding two additional PQC KEM rounds with ML-KEM-768 (lattice) and
BIKE-L3 (code-based), one after the other, creates an encryption key based on three KEM
technologies and provides protection for future attacks using Shor’s algorithm. Adding
at least two PQCs to the DH key exchange provides a higher protection level against a
single KEM failure and can help resist quantum attacks for a longer duration. In
addition, using KEMs based on different types of mathematics can protect against future
vulnerabilities against a specific type of PQC, such as all PQCs based on lattice
technology.
The transition to the post-quantum world where PQCs are the only key exchange
mechanism will take many years as the industry needs time to validate the new PQCs and
gain confidence in their security abilities. During the transition period, hybrid keys
based on RFC 9242 and RFC 9370 will be standard.
The standards process to approve new PQCs will come in phases, with NIST
approving groups of PQCs for each approval round. As each PQC has performance and
security tradeoffs, gaining an understanding of how each PQC performs is needed to
determine which technology is best suited for the different security use cases. For
example, Classic McEliece has proven itself as a very secure PQC over time, but the
tradeoff for its high security is the large keys sizes it uses, which can limit Classic
McEliece use in VPN and TLS communications.
World governments are recommending a security level of L3 or above to
provide strong security and resistance to future quantum computer attacks.
During the transition period from classic encryption to post-quantum
encryption, cryptographic agility will be required to allow rapid replacement of any
compromised PQCs. Palo Alto Networks RFC 9242 and RFC 9370 post-quantum KEM solution
provides a broad set of PQCs to achieve cryptographic agility from the beginning,
allowing customers to select and remove any supported PQC from the IKEv2 key negotiation
quickly without any software updates or changes to the existing network.
The following PQCs are supported for PAN-OS IKEv2:
ML-KEM (Kyber) 512, 768, 1024
FrodoKEM 640-aes, 640-shake, 976-aes, 976-shake, 1344-aes,
1344-shake
Classic McEliece 348864, 348864f
The benefits of RFC 9242 and RFC 9370 include:
Approved standards with multivendor support.
High scalability with dynamic key exchange instead of RFC 8784’s static
PPKs.
Support for a broad range of PQC KEMs.
IKEv2 backward compatibility allows fallback if the peer can’t support
the RFCs.
Hybrid keys are more resistant to Shor’s algorithm as different PQC
technologies can be used together.
Can be layered with RFC 8784 for quantum defense-in-depth and
cryptographic agility.
The disadvantages of RFC 9242 and RFC 9370 include:
Early PQC standardized lists might not provide enough PQCs to achieve
cryptographic agility at the beginning of the PQ transition.
New PQC might need many years to be fully vetted and trusted by
industry.
Multiple KEMs can add additional overhead and slow the IKEv2 peering
process.
New PQC KEMs can cause fragmentation as key sizes and data payloads are
larger.
Not every device can be upgraded to support PQC KEMs.
Risk of Denial of Service (DoS) attacks can increase with the extended
key exchange during the IKE_INTERMEDIATE due to the increased resources needed
before the initiator is authenticated.
Hybrid keys are designed to protect against harvesting attacks where
the encrypted information is saved and decrypted with a cryptographically
relevant quantum computer (CRQC) at a later date. Attacks using a quantum
computer in an active attack are not completely solved with hybrid keys for the
following reasons:
Authentication is still performed using classical methods,
either pre-shared key or digital signature algorithms. Pre-shared keys
must be long and complex to be post-quantum secure, but they’re not
scalable. Authentication with digital signatures must be performed with
a post-quantum digital signature.
PQCs are designed to provide resistance to harvesting attacks
and until CRQCs become available, attacking the authenticity of a
connection does not matter because there are no possibilities for
exploitation as these only occur at the time of connection.
It's recommended that you use RFC 9242 and RFC 9370 based IKEv2 VPNs to secure
VPN connections against post-quantum threats by using hybrid keys based on multiple KEM
technologies. With a broad set of PQCs, cryptographic agility can be achieved to
safeguard against compromised PQCs during the transition to a post-quantum world.
