Sigstore

Free public signing and transparency infrastructure for open source artifacts

As of 31 August 2026, Sigstore is free to use. An OpenSSF project providing a free certificate authority and public transparency log, run as a public good on a 99. Softwr lists it under Cybersecurity. Sigstore is made by Open Source Security Foundation, Linux Foundation, available on Web, Linux, macOS, Windows.

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Overview

What Sigstore does

Sigstore is the umbrella for the components that make keyless signing work: Fulcio, a certificate authority that issues short-lived certificates against an OIDC identity, Rekor, an append-only transparency log recording every signature, Cosign as the client, plus a timestamp authority, a policy controller and clients across most major languages. It is governed under the Open Source Security Foundation at the Linux Foundation, with contributions from Google, Red Hat, Chainguard, GitHub and Purdue University, and everything is Apache 2.0. The public instance is free to everyone, which is the point and also the exposure. It runs to a 99.5 percent availability objective, which is an objective and not an agreement: there is no contract, no remedy and no escalation path beyond a Slack channel and GitHub issues. If a build pipeline signs on every commit and Fulcio is unavailable, builds fail; if an admission controller verifies online, deploys fail. Certificates are valid for ten minutes, so verifying anything older depends on the log entry proving the signature happened inside that window, which couples artifact trust to the permanent availability of a free service. One detail is easy to get wrong and worth stating precisely. Rekor version 2 reached general availability in October 2025, but the public instance still runs version 1 as its default log and the project has said it will for the foreseeable future, bundling that disruption with a later post-quantum migration rather than breaking clients twice. Anyone who read the availability announcement and assumed the flagship instance had migrated is mistaken.

What people use it for

Open source projects signing releases without running a certificate authority
Organisations meeting a signed-artifact requirement without buying a signing product
Publishing provenance that a consumer can verify independently of you
Self-hosting the same components where a public log is unacceptable

Where it falls short

Concrete and checkable, so you can decide whether any of them matter to you. This is the half of a review a vendor will not write about Sigstore.

The security model depends on somebody watching the log. The documentation states that compromise of an identity provider or of Fulcio itself is detectable only if third parties monitor the transparency log, the monitoring tool is a community-tier rather than core project, and almost no consumer runs one.
It is a 99.5 percent objective with no service level agreement, which permits several hours of downtime a month and offers no remedy. A pipeline that signs on every build has taken a hard dependency on a free service with no contract behind it.
Log scale is a live engineering problem rather than a theoretical one. The active shard holds billions of entries, the log has already been sharded twice, and sharding version 1 requires stopping traffic, which is why a replacement was built.
Ten-minute certificates make trust depend on log availability. Verifying an older signature relies on the log entry proving it was made inside that window, so a lost or unreachable entry can render a valid artifact unverifiable.
Migration debt is substantial and ongoing. Version 2 of the log is generally available but not the public default, the signing client has an announced breaking release ahead, some official clients lag the new log format, and a post-quantum migration is named as the next break after that.

Cross-shopped

What people choose instead of Sigstore

Each pairing was judged by two reviewers asking whether a buyer would genuinely weigh the two against each other. The ones that failed were deleted rather than published.

Sigstorevs
Cosign
Cosign: The client, if what you need is the signing command rather than the infrastructure
Sigstorevs
Syft
Syft: A different question entirely: what is inside the artifact rather than who signed it

Pricing

What Sigstore costs

Taken from the vendor's own pricing page. Prices move, so check before you buy.

Public good instance

Free

Free to everyone with no contract
99.5 percent availability objective, not an agreement
100KB cap per attestation upload
Support is a Slack channel and GitHub issues

Self-hosted

Free

Apache-2.0
Run your own Fulcio and Rekor
Rekor v2 available for self-hosters
Infrastructure and operation are yours

Capabilities

Features

Fulcio
A free certificate authority issuing ten-minute certificates against an OIDC identity
Rekor
An append-only public transparency log of signatures, sharded and running to billions of entries
Keyless signing
No long-lived private key to store, rotate or lose
Multi-language clients
Official clients in Go, Python, JavaScript, Java, Rust and others
Timestamp authority
Independent timestamping for signatures
Neutral governance
OpenSSF and Linux Foundation oversight rather than a single vendor

Answered, with sources

Questions people ask

Each answer names the page it came from, so you can check it rather than take our word for it.

Is the public instance really free?

Yes, with no contract and no paid tier. That is also the weakness: a 99.5 percent objective with no agreement, no remedy and support through Slack.

Has the public log moved to Rekor v2?

No. Version 2 reached general availability in October 2025 and self-hosters can use it, but the public instance still defaults to version 1 and the project has said it will for the foreseeable future.

Does Sigstore make my dependencies safe?

No, and this is a category error worth avoiding. It tells you who published something. It has no knowledge of what the artifact contains or whether it is vulnerable.

What are the rate limits?

Not published. Only the 100KB cap per attestation upload is documented, so do not design a high-volume pipeline around assumed throughput.

Should we self-host it?

If a public record of every signature is unacceptable, or if a free service with no agreement cannot sit in your build path, then yes. Otherwise the public instance is what most projects use.

Keep looking

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Softwr does not host reviews and shows no star rating for Sigstore, because a rating we did not collect is not ours to publish. What is here is the pricing and platform detail from the vendor’s own pages, limitations we could state concretely, and alternatives a reviewer confirmed people weigh against it. Tell us if any of it is wrong.

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