Not possible to create cert for quantum-safe algorithm | error "invalid argument"

[abcnorio]

Hello,

• OS Debian bookworm
• openssh quantum-safe build worked just fine (git from 2026-03-18)

$ openssl --version
OpenSSL 3.0.13 30 Jan 2024 (Library: OpenSSL 3.0.13 30 Jan 2024)

creating keys works:

$ ./ssh-keygen -t ssh-slhdsapuresha2128f -C "root-PQ@ca.com" -N "" -f rootca-PQ
[...]
$ ./ssh-keygen -t ssh-slhdsapuresha2128f -C "signer-PQ@ca.com" -N "" -f signer-PQ
[...]

does not work:

$ ./ssh-keygen -s rootca-PQ -I signer-cert-PQ@ca.com signer-PQ.pub
Could not upgrade key signer-PQ.pub to certificate: invalid argument

Using a non quantum-safe algorithm everything works:

./ssh-keygen -t ed25519 -C "root@ca.com" -N "" -f rootca-ed25519
[...]
./ssh-keygen -t ed25519 -C "signer@ca.com" -N "" -f signer-ed25519
[...]
./ssh-keygen -s rootca-ed25519 -I signer-cert@ca.com signer-ed25519.pub
Signed user key signer-ed25519-cert.pub: id "signer-cert@ca.com" serial 0 valid forever
$ ls|grep cert
signer-ed25519-cert.pub

This can be reproduced for other algorithms as well, e.g. ssh-falcon512

Thanks!

[alharrison]

abcnorio, thanks for sharing the issue. I believe this wasn't implemented in this fork before @andrewyounkers and I became contributors. We spoke briefly about this and could add this support, but we unfortunately are both a little tied up at the moment. Is this urgent for your needs?

Thanks!

[abcnorio]

It is not urgent and I fully appreciate your work and understand what "limited time" means (we all suffer from that) - if at one point it works that would be great! At the moment I use ed25519 and it doesn't look like the quantum computers are already out there that can break rsa etc. in minutes :-). Later ed25519 can be just replaced by some other PQ algorithm.