Public rdiff Signatures: Safe?

TL;DR

Yes, you can make an rdiff signature public without disclosing the contents of the file it represents. The signature itself is a cryptographic hash and metadata about *changes* between versions, not the full file data.

How rdiff Works (Briefly)

rdiff stores differences between files rather than complete copies. It uses a signature to identify these changes. The signature doesn’t contain the actual file content; it contains information about what *has* changed, allowing efficient updates and backups.

Steps to Safely Publish an rdiff Signature

1. Generate the Signature: Use the standard rdiff command to create a signature file. For example:

   rdiff --signature-file my_file.sig my_file

   This creates a file named `my_file.sig` containing the signature.

2. Verify Signature Integrity: Before publishing, verify that the signature is valid for the original file:

   rdiff --verify my_file.sig my_file

   This confirms no tampering has occurred during signature creation.

3. Publish the Signature File: You can now safely publish `my_file.sig` to a public location (e.g., a website, repository). It does *not* reveal the contents of `my_file`.
4. Consider Delta Compression: rdiff uses delta compression to store changes efficiently. The deltas themselves are also not the full file content but represent differences. Publishing these deltas is generally safe as well, though it’s good practice to understand what you’re sharing.
5. Understand Metadata: The signature file includes metadata like timestamps and file sizes. This information *is* public when you publish the signature. If this metadata is sensitive (e.g., reveals creation dates that are confidential), consider whether publishing the signature is appropriate.

What the Signature Does NOT Contain

• Full File Content: The signature does not store the complete contents of the file being backed up or versioned.
• Raw Data: It doesn’t contain the actual binary data of the file.

Security Considerations

• Man-in-the-Middle Attacks: Ensure you are obtaining signatures from a trusted source to prevent someone substituting a malicious signature.
• Signature Algorithm Strength: rdiff uses cryptographic hashes. Ensure the hash algorithm used is strong (e.g., SHA256 or better). Older algorithms like MD5 are considered insecure.
• cyber security best practice: Regularly review your cyber security practices and update rdiff if vulnerabilities are discovered.