--- title: "Mutual Post-Quantum Auth over IKEv2 – IPsec Series, Part 8" url: https://daily.dev/posts/mutual-post-quantum-auth-over-ikev2-ipsec-series-part-8-xm1etcoxb source_url: https://blogs.cisco.com/developer/mutual-post-quantum-auth-over-ikev2-ipsec-series-part-8 type: article source: "Cisco" published: 2026-08-24T19:45:04.920Z updated: 2026-08-24T19:45:35.360Z tags: ["security", "quantum-computing"] reading_time: 8 upvotes: 1 comments: 0 language: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Mutual Post-Quantum Auth over IKEv2 – IPsec Series, Part 8 **[Cisco](https://daily.dev/sources/cisco)** · 8 min read · 1 upvotes · 0 comments ## Summary A hands-on lab walks through mutual authentication over an IKEv2 tunnel using two Docker containers, first with classical ECDSA certificates on stable strongSwan, then with post-quantum ML-DSA-44 certificates on strongSwan's experimental ml-dsa branch. Both runs use an ML-KEM-based hybrid key exchange, but only the second achieves fully post-quantum authentication. The ML-DSA leaf certificate plus signature balloons the IKE_AUTH message to about 6.9 KB, splitting into 6 fragments versus a single ~900-byte packet for ECDSA, illustrating why fragmentation support is essential and where current reassembly bugs live. The piece closes by noting that ML-DSA authentication is only available on an experimental branch, the composite/hybrid signature work is separate, and the IETF wire-format draft is still evolving, so post-quantum IKEv2 authentication remains an emerging capability rather than production-ready. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Can I authenticate a strongSwan IKEv2 VPN with ML-DSA today? Yes, but only on strongSwan's experimental ml-dsa branch (PR #2626), not in the stable 6.0.x release line. The branch supports mldsa44/65/87 key types through its pki tool, and swanctl.conf needs no changes since auth = pubkey is algorithm-agnostic and detects the key type from the certificate. Composite/hybrid signatures are being developed separately on a pq-composite-sigs branch, and the IETF IKEv2 PQC-auth wire format draft is still evolving. _Track strongSwan's post-quantum authentication progress on daily.dev before betting a VPN rollout on it._ ### Why does ML-DSA certificate authentication in IKEv2 need message fragmentation? An ML-DSA-44 leaf certificate (roughly 4 KB DER) plus its signature pushes the IKE_AUTH message to about 6.9 KB, which splits into 6 fragments on the wire, compared to a single ~900-byte unfragmented packet for the ECDSA equivalent. This size explosion is why fragmentation = yes is required, and larger variants like ML-DSA-65/87 or an added intermediate CA can push the fragment count into known strongSwan reassembly bugs (issue #2889). _Developers sizing post-quantum VPN handshakes can follow fragmentation gotchas like this on daily.dev._ ### Is the ML-KEM key exchange in strongSwan already usable in production? Yes, ML-KEM-based hybrid key exchange (for example CURVE_25519/KE1_ML_KEM_768) ships in stable strongSwan and works out of the box, unlike post-quantum authentication which remains experimental. This means the key-exchange side of an IKEv2 tunnel can already be made quantum-safe today while the certificate-based authentication side still relies on classical ECDSA in real-world deployments. _Follow which post-quantum VPN building blocks are production-ready versus experimental on daily.dev._ ## Similar posts on daily.dev - [Watch a Hybrid Post-Quantum Handshake on the Wire – IPsec Series, Part 4](https://daily.dev/posts/watch-a-hybrid-post-quantum-handshake-on-the-wire-ipsec-series-part-4-rpovq4vpj) · Cisco · 0 upvotes · 0 comments - [Who Goes There? Post-Quantum Authentication – IPsec Series, Part 6](https://daily.dev/posts/who-goes-there-post-quantum-authentication-ipsec-series-part-6-iskqiozsb) · Cisco · 0 upvotes · 0 comments - [The Great Certificate Size Explosion – IPsec Series, Part 7](https://daily.dev/posts/the-great-certificate-size-explosion-ipsec-series-part-7-qqoeuqaeo) · Cisco · 1 upvotes · 0 comments --- Tags: [#security](https://daily.dev/tags/security), [#quantum-computing](https://daily.dev/tags/quantum-computing) [View this post on daily.dev](https://daily.dev/posts/mutual-post-quantum-auth-over-ikev2-ipsec-series-part-8-xm1etcoxb)