How to verify a downloaded file's signature

Confirm a release, document, or any download really came from the signer and wasn't tampered with, by checking it against its detached PGP signature, right on your phone.

~3 minutes iOS / Android Signer key required
At a glance
  1. Get the file and its .sig / .asc
  2. Import the signer's public key
  3. Verify the signer's fingerprint
  4. Share both files into PGPony
  5. Read the verification result
Prerequisites
  • PGPony installed
  • The downloaded file and its detached signature
  • The signer's public key, with a fingerprint you can verify against a trusted source
Step 1

Get both files

Download the file and its detached signature, usually a second file with the same name plus .sig or .asc (for example release.tar.gz and release.tar.gz.asc). Verification needs both; the signature alone or the file alone isn't enough.

Step 2

Import the signer's public key

The signer's public key has to be in your PGPony keyring. Import it from their key file, a keyserver lookup, or wherever they publish it. See Import a GnuPG key to your phone if you need it.

Step 3

Verify the signer's fingerprint

Before you trust a verification result, make sure you have the right key. Compare the key's fingerprint against the one the project or person publishes through a channel you trust: their website, a signed announcement, in person. A valid signature from the wrong key proves nothing.

This is the step that matters The cryptography is only as trustworthy as your verification of whose key you're checking against.
Step 4

Open the verify flow

Share both the original file and its signature into PGPony (via the Share Sheet on iOS or the share intent on Android), or open them from the Decrypt tab. PGPony pairs the file with its detached signature and runs verification.

Step 5

Read the result

PGPony reports one of three states: valid and signer known (a green result; the file is intact and signed by a key in your keyring), valid but signer unknown (the math checks out but you haven't marked the key as trusted; verify the fingerprint), or invalid (the file changed, the wrong signature was used, or the wrong key; don't trust it).

What each result means

  • Valid, known signer: the file is unmodified and signed by a key you trust. Safe to use.
  • Valid, unknown signer: intact and correctly signed, but you haven't verified whose key this is. Check the fingerprint before trusting.
  • Invalid: the file was altered, the signature doesn't match, or you used the wrong key. Re-download and recheck.

Common questions

What does a valid signature prove?

That the file is unchanged and signed by the holder of a specific private key. Who that is depends on you verifying the key's fingerprint out of band.

What's a detached signature?

A separate signature file alongside the original, so the original stays unmodified. You need both to verify.

Verification failed. Now what?

Don't trust the file. Re-download both file and signature from the source, and confirm you have the correct signer key.

Valid but unknown signer?

The signature is good, but the key isn't one you've trusted. Verify its fingerprint against the project's published fingerprint.

Next steps

Get PGPony

Free OpenPGP encryption for iOS and Android. No accounts, no tracking.