Secure Software Supply Chain

Mansfeld-Südharz, Germany - December 1, 2025

Inside the county-wide pipeline that turns upstream commits into signed, SBOM-tagged artifacts before they ever reach a production PLC

The first rule we give every new supplier is simple: bring code, not confidence. Confidence is what we manufacture locally, in a low-slung brick building that used to store anhydrous ammonia for the old Buna rubber plant. Today the air smells of warm electronics instead of acrid latex, and the only thing under pressure is a row of GitLab runners wired to a clock that beats to DCF77 time. Every upstream library, container base image or firmware blob enters through a loading dock that looks more like a postal customs office than a software reception: tamper-evident seals, chain-of-custody slips, and a notary stamp that carries the same legal weight as a shipping manifest for hazardous chemicals. The ritual feels theatrical until you realise that a malicious dependency is essentially a slow-motion explosion—silent, invisible, but capable of shutting down the same chemical lines that once employed half the county.

Our verification furnace begins with a single source of origin: the supplier must deposit source archives into a hardened Git forge hosted on an air-gapped subnet reachable only through mutually authenticated TLS channels terminated inside an HSM. The forge itself runs on immutable append-only storage; once a commit hash is written, even root cannot amend history without triggering an alarm that pages the county’s emergency operations centre. That may sound excessive for a rural cluster, but the physics of trust are unforgiving: if an attacker can rewrite history, he can rewrite recovery plans, and in a region where 40 % of GDP still rides on continuous-process chemistry, recovery is not an abstraction—it is the difference between warm homes and frozen pipes in January. The moment the archive lands, a build worker—physically present in the building, no remote access—inserts a USB hardware token that holds the supplier’s public signing key, verifies the signature against an external key directory maintained by the German Federal Network Agency, and only then tags the commit as “origin-verified.” The tag itself is time-stamped with a RFC 3161 token issued by a regional trust centre whose clock is synchronised to the same DCF77 signal, ensuring that any back-dating attempt would require compromising both the cryptographic and the radio layer, a hurdle high enough to make most adversaries look for softer targets.

From origin we move to reproducibility. The forge triggers a hermetic build inside a NixOS environment whose entire closure—including compiler, linker, kernel headers and even the build script itself—is pinned to a cryptographic hash recorded in a ledger stored on an optical WORM disk. The ledger is append-only and kept in a fireproof safe that once stored cyanide catalyst recipes; the irony is not lost on us. If the byte-for-byte binary produced by this build does not match the hash published by the supplier, the pipeline halts and emits a diffoscope report that is automatically forwarded to both the supplier and the county’s procurement office. In the first twelve months we have rejected 3 % of all submissions, most of them benign—timestamp differences, build-path variations—but two packages contained undeclared network calls that would have phoned home to domains registered in jurisdictions with no MLAT route to Germany. Those two rejections alone paid for the entire build farm, because the cost of a single undetected exfiltration from a local chemical park would have dwarfed the county’s annual IT budget.

Once reproducibility is proven, the artifact enters the attestation layer. We generate an SBOM in SPDX format that lists every transitive dependency down to the static libraries linked into Go binaries. Each entry is cross-referenced against the federal vulnerability database maintained by the BSI, but we do not stop at CVE matching; we also run a semantic diff that flags API additions that could be used for future supply-chain attacks—new HTTP clients, new file-extension handlers, new reflection paths. These potential behaviours are translated into a finite-state machine and compared against a policy written in Rego that encodes the county’s security baseline: no outbound connections except to NTP and OCSP, no execution of downloaded scripts, no writes outside /tmp and /var/lib. If the state machine can reach a forbidden transition, the pipeline refuses to sign the container image, and the rejection reason is published in a public log that suppliers can query without exposing the proprietary code itself. The transparency is deliberate: we want vendors to learn what “secure by design” means in practice, not just in marketing slides.

"Trust is no longer imported; we distil it here, one signed artifact at a time."

Signing itself is a ceremony that merges legal and technical evidence. The final binary is hashed with BLAKE3, the digest is embedded into a PDF certificate that also contains the SBOM fingerprint, the build log hash, and the name of the build engineer who witnessed the process, and the certificate is co-signed with a qualified electronic signature issued by a trust service provider under eIDAS. The resulting document is legally equivalent to a notarised contract, which means that if a later audit discovers malfeasance, the county can recover damages without having to prove negligence in open court; the signature itself is prima facie evidence that the supplier delivered code that met the agreed specification. This single clause has halved the average negotiation time for new framework agreements, because general counsels on the vendor side recognise that resisting the process is more expensive than submitting to it.

Finally, distribution is local by default. The signed artifact is pushed to aHarbor registry that runs inside the county’s own data centre, physically 800 metres from the build forge. A second instance is maintained at the university’s super-computing facility for redundancy, but both replicas share the same root certificate, and both are reachable only through layer-2 circuits that ride the county’s municipal fibre network. Outbound mirrors to Docker Hub or GitHub Packages are disabled; if a developer in a partner SME wants to pull the image, she must route through the county’s VPN, which in turn requires hardware-based MFA issued by the local trust centre. The topology guarantees that even if a global package repository is hijacked, the production systems inside the chemical parks continue to receive authentic bytes, because the only path to update is the one that passes through our notary, our time-stamp and our signature chain. In effect we have recreated the logistics logic of just-in-time manufacturing for software: parts arrive exactly when needed, and every shipment carries a tamper seal that can be traced back to the shift that assembled it.

The cultural side-effect is harder to measure but impossible to ignore. Suppliers who once treated “security” as a checkbox now schedule plant visits to watch their own code being compiled, signed and stored. They see the same operators who once weighed rubber additives now weighing cryptographic entropy, and the metaphor lands: quality is not something you bolt on before shipping; it is something you bake into the recipe. After six months of operation, three major vendors have voluntarily rewritten their build pipelines to match our reproducibility standard even for products that never touch the county’s infrastructure, simply because they no longer want to maintain two versions of truth. That is the real output of the supply-chain furnace: not just secure code, but a community of suppliers who have internalised the idea that trust is produced locally, stored locally and verified locally—exactly the chemistry that turned anhydrous ammonia into digital resilience without ever asking the county to trust a stranger again.

The Cyber Resilience Alliance is a public-private partnership established 2025, led by CypSec, Validato and the County of Mansfeld-Südharz. The Alliance operates a sovereign private-cloud security stack, a shared SOC and an cyber academy, aiming to make Mansfeld-Südharz the reference site for rural cyber resilience by 2030.

Media Contact: Daria Fediay, Chief Executive Officer at CypSec - daria.fediay@cypsec.de.