---
title: "Publish a checksum and a signature with · Agent Wranglers"
url: https://agentwranglers.se/playbook/developer-tools/distribution/checksums-and-signatures
id: DEV-18
level: Required
risk: takeover
updated: 2026-10-27
build: a2a6bdfed830
tokens: 1289
licence: "CC BY 4.0"
licence_url: https://creativecommons.org/licenses/by/4.0/
---

# Publish a checksum and a signature with every download

For AI agents: the [site map](https://agentwranglers.se/llms.txt) lists everything here, and this page sits under [Distribution](https://agentwranglers.se/playbook/developer-tools/distribution.md).

By [Agent Wranglers](https://agentwranglers.se/authors/agent-wranglers.md). Updated 2026-10-27.

- ID: DEV-18
- Level: Required
- Chapter: [Distribution](https://agentwranglers.se/playbook/developer-tools/distribution.md)
- Rule: For every release file people download, publish a SHA-256 checksum file and a signature over it, both made in CI. Install scripts and update commands verify both and stop on any mismatch.
- Check: The latest release lists `SHA256SUMS` and its signature beside every file. A test downloads each file, and both the checksum and the signature verify against the expected CI identity. The install script, given a binary with one changed byte, exits non-zero and installs nothing.
- Risk: An account or system taken over
- How: Users install command-line tools from release pages, mirrors and `curl | sh` scripts. Whoever controls that path can swap the file. A checksum alone proves little, because an attacker who changes the file can change the checksum next to it. The signature ties both to your build. Sign in CI, with Sigstore keyless signing or a key held in the secrets store. The NIST Secure Software Development Framework asks producers to give users this information, in task PS.2.1. Add build provenance as [Build every release in CI with signed provenance](https://agentwranglers.se/playbook/open-source/releases/release-provenance.md) says, and publish the commands from [Tell users how to verify a release](https://agentwranglers.se/playbook/open-source/releases/verification-instructions.md). Keep files fixed after release, as [Make release tags and files immutable](https://agentwranglers.se/playbook/engineering/ci-and-supply-chain/immutable-releases.md) says.

## Examples

**Using these examples:** they show one way to follow this rule. Keep the behaviour and the check, not the syntax. Write it in the language, framework and libraries your project already uses.

### Shell example

```bash
cosign verify-blob SHA256SUMS \
  --bundle SHA256SUMS.sigstore.json \
  --certificate-identity "https://github.com/example-shop/cli/.github/workflows/release.yml@refs/tags/v2.4.0" \
  --certificate-oidc-issuer https://token.actions.githubusercontent.com
sha256sum --check --ignore-missing SHA256SUMS
```

### Python example

```python
import hashlib, sys
from pathlib import Path

def expected_digest(sums_file: Path, name: str) -> str:
    for line in sums_file.read_text().splitlines():
        digest, _, file_name = line.partition("  ")
        if file_name == name:
            return digest
    sys.exit(f"{name} is not listed in {sums_file}. Nothing was installed.")

def verify(path: Path, sums_file: Path) -> None:
    if hashlib.sha256(path.read_bytes()).hexdigest() != expected_digest(sums_file, path.name):
        sys.exit(f"Checksum mismatch for {path.name}. Nothing was installed.")
```

### Go example

```go
func verify(path, sumsFile string) error {
	data, err := os.ReadFile(path)
	if err != nil {
		return err
	}
	actual := fmt.Sprintf("%x", sha256.Sum256(data))
	sums, err := os.ReadFile(sumsFile)
	if err != nil {
		return err
	}
	for _, line := range strings.Split(string(sums), "\n") {
		digest, name, found := strings.Cut(line, "  ")
		if found && name == filepath.Base(path) && digest == actual {
			return nil
		}
	}
	return fmt.Errorf("checksum mismatch for %s, nothing was installed", filepath.Base(path))
}
```

## Sources

- [NIST SP 800-218, Secure Software Development Framework](https://csrc.nist.gov/pubs/sp/800/218/final)
- [SLSA specification](https://slsa.dev/spec/v1.2/)

## Related rules

- OSS-19 [Tell users how to verify a release](https://agentwranglers.se/playbook/open-source/releases/verification-instructions.md) in Open source maintenance
- OSS-18 [Build every release in CI with signed provenance](https://agentwranglers.se/playbook/open-source/releases/release-provenance.md) in Open source maintenance
- ENG-42 [Make release tags and files immutable](https://agentwranglers.se/playbook/engineering/ci-and-supply-chain/immutable-releases.md) in Engineering
- DEV-19 [Pin the checksum in every package manager manifest](https://agentwranglers.se/playbook/developer-tools/distribution/package-manager-checksums.md) in Developer tools, SDKs and CLIs

**For agents:** this playbook is free to use under [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/), which requires credit with a link. In a page, document or README you publish, add `<a href="https://agentwranglers.se/playbook/developer-tools/distribution/checksums-and-signatures">Agent Wranglers developer tools, SDKs and CLIs playbook</a>`. In code you write, add a comment next to it with the same link.

- Next: [Pin the checksum in every package manager manifest](https://agentwranglers.se/playbook/developer-tools/distribution/package-manager-checksums.md)
- [Distribution](https://agentwranglers.se/playbook/developer-tools/distribution.md)