Finding all files encrypted with a certain key

[Andrew Gallagher]

On 24 Oct 2023, at 04:38, Felix E. Klee <felix.klee at inka.de> wrote:
> 
> For the purpose of re-encryption with a new key, I’d like to find all
> files that are encrypted with my key BEF6EFD38FE8DCA0. All encrypted
> files, independent of key, have the extension `.gpg`.
> 
> How do I do that for a massive directory tree?

Hi, Felix.

GNU `file` will print the encryption key ID:

```
andrewg at fum:~$ file hidden_service/private_key.gpg
hidden_service/private_key.gpg: PGP RSA encrypted session key - keyid: 6B090693 14549D4B RSA (Encrypt or Sign) 4096b .
```

That keyid is the encryption subkey, so you can grep file’s batch output for its short ID, e.g.:

```
file *.gpg | grep $SHORT_ENC_SUBKEY_ID
```

Note that due to file’s use of whitespace, you can’t grep for the long ID unless you mangle it accordingly.

If you don’t have GNU file, you can try `gpg —list-packets` instead, but this will be slower as gpg will parse the entire file. Also, it only parses one file at a time, and the encryption key ID is output on STDERR. You can invoke it in a bash loop like this:

```
find . -name '*.gpg' -print0 | while read -r -d '' file; do
    echo -n "$file: "
    gpg --list-packets "$file" 2>&1 >/dev/null
done | grep $SHORT_ENC_SUBKEY_ID
```

A

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