# OpenSSH 10.6 turns on hybrid post-quantum signatures and disables compression to cut side-channel risk OpenSSH 10.6 changes security behaviour operators can actually feel: hybrid ML-DSA/Ed25519 signatures are enabled, the LZ77 dictionary coder is disabled to reduce side-channel exposure, and scp's remote-to-remote -R path starts its deprecation. The release is more than routine maintenance. OpenSSH is changing cryptographic defaults, sacrificing some compression effectiveness for side-channel safety, and warning that AI-assisted security reports are pushing it toward a faster release cadence. - Status: Active - Published: 2026-10-07T10:27:45+13:00 - Updated: 2026-10-07T10:27:45+13:00 - Categories: Web Development, Cloud & Infrastructure, Compute & AI Infrastructure, Deployment & DevOps, Developer Tools - Tags: OpenSSH, post-quantum cryptography, security hardening, SSH - Canonical HTML: https://beyondthe.news/dossiers/openssh-10-6-post-quantum-signatures-compression-scp-r ## What changed OpenSSH 10.6 was released on October 6, 2026. It enables the hybrid ssh-mldsa44-ed25519 signature algorithm, combining ML-DSA-44 with Ed25519. The project also disables the LZ77 dictionary coder used by ssh and sshd compression to mitigate side-channel information leakage, reducing the effectiveness of the Compression option. The scp -R mode for copying between two remote hosts is deprecated because of security risks and is intended to be ignored in a future release. OpenSSH also says a large volume of AI-assisted security reports is leading it to make more frequent releases rather than batch fixes for the next planned version. ## Why it matters SSH sits underneath routine server administration, CI/CD and automated infrastructure access, so changes to its cryptographic and transport defaults have a wide operational blast radius. Post-quantum signatures move another everyday infrastructure protocol toward hybrid cryptography without requiring operators to invent their own scheme. Disabling the compression dictionary deliberately trades compression efficiency for a tighter side-channel boundary, while scp -R deprecation matters to scripts that still depend on remote-to-remote copies. ## Hybrid post-quantum signatures become available by default OpenSSH 10.6 enables ssh-mldsa44-ed25519, a hybrid signature that combines ML-DSA-44 with Ed25519. Hybrid construction keeps a conventional signature alongside the post-quantum algorithm rather than betting the authentication path on a single newer primitive. ## Compression gives up efficiency for a smaller side-channel surface The LZ77 dictionary coder in ssh and sshd is disabled. Compression still exists, but the change reduces how much repeated-data history can influence compressed output, at the cost of less effective compression. ## scp -R is on the way out The remote-to-remote scp -R mode is deprecated on security grounds. Operators with automation that copies directly between two remote systems should identify those workflows before a later OpenSSH release ignores the option. ## AI-assisted vulnerability reports are changing release cadence The OpenSSH project says it is receiving many AI-assisted security reports and welcomes them when paired with human triage, analysis, tests and especially fixes. Rather than accumulate verified fixes for scheduled releases, it expects to release more frequently. ## Key details - OpenSSH 10.6 was released October 6, 2026. - The hybrid ssh-mldsa44-ed25519 signature algorithm is enabled. - The LZ77 dictionary coder is disabled in ssh/sshd compression to mitigate side-channel leakage. - Compression may therefore be less effective. - scp -R remote-to-remote copying is deprecated and is planned to be ignored in the future. - OpenSSH says AI-assisted security reports are contributing to a more frequent release cadence. ## Builder takeaways - Inventory scripts that depend on scp -R before its future removal changes behaviour. - If SSH compression matters on constrained links, test 10.6 rather than assuming previous compression ratios. - Treat hybrid post-quantum authentication as an interoperability change: confirm both ends and policy tooling understand the algorithm before requiring it. - For AI-assisted vulnerability reporting, OpenSSH's message is clear: human triage, reproducibility, tests and fixes matter more than raw generated reports. ## What to watch - When scp -R becomes ignored rather than merely deprecated. - Distribution adoption of OpenSSH 10.6 and whether downstream defaults differ. - Interoperability and policy guidance for ssh-mldsa44-ed25519. - Whether the faster security-driven release cadence becomes sustained. ## Uncertainties - Distribution packaging may enable or disable features differently from upstream OpenSSH. - The project has not specified the exact future release in which scp -R will be ignored. - The effect of disabled LZ77 dictionary coding depends on workload and whether SSH compression is used. ## Sources - [OpenSSH 10.6 release notes](https://www.openssh.com/txt/release-10.6) — OpenSSH · primary · 2026-10-06T00:00:00+13:00. Upstream release notes for cryptographic, compression, scp and security-reporting changes. - [OpenSSH 10.6 released](https://lwn.net/Articles/1098980/) — LWN.net · independent specialist · 2026-10-06T00:00:00+13:00. Independent specialist summary confirming the release and notable security/compatibility changes. - [OpenSSH 10.6 Released with Security Hardening, Post-Quantum Support](https://linuxiac.com/openssh-10-6-released-with-security-hardening-post-quantum-support/) — Linuxiac · independent specialist · 2026-10-06T00:00:00+13:00. Discovery item and additional operational context.