To enforce gpg --verify to only consider the specific public key 9F85796A16D64CC33CF084CA1E70BBC37279E5AB and reject all others, you can use the --keyring option to specify a custom keyring containing only that key. Here's how:

Step-by-Step Solution

1. Export the Specific Key to a Temporary Keyring

Extract the key 9F85796A16D64CC33CF084CA1E70BBC37279E5AB into a temporary keyring file:

gpg --no-default-keyring --keyring ./temp-keyring.gpg --export 9F85796A16D64CC33CF084CA1E70BBC37279E5AB

This creates a file temp-keyring.gpg containing only the specified key.

2. Verify the Signature Using the Temporary Keyring

Use the temporary keyring to verify the signature. This ensures only the specified key is considered:

cat signature | gpg --no-default-keyring --keyring ./temp-keyring.gpg --verify

• --no-default-keyring: Ignores the default keyring.
• --keyring ./temp-keyring.gpg: Uses only the temporary keyring.

3. (Optional) Clean Up

After verification, you can delete the temporary keyring:

rm ./temp-keyring.gpg

Why This Works

• By using a custom keyring with only the desired key, gpg cannot use any other keys for verification.
• The warning This key is not certified with a trusted signature! will still appear (unless you explicitly trust the key), but the verification will only succeed if the signature matches the specified key.

Alternative: Use --trusted-key

If you want to trust the key for this session (and suppress the warning), you can use:

cat signature | gpg --trusted-key 9F85796A16D64CC33CF084CA1E70BBC37279E5AB --verify

However, this does not enforce exclusivity—it only suppresses the warning. The first method (custom keyring) is stricter.