Decrypt only if signed

[Hardeep Singh]

Hi

I am writing a batch script and the basic requirement is that GPG
should only decrypt the file if its signed by using one of the keys in
the keyring. If it has not been signed, just encrypted, it should
leave it encrypted and not decrypt it.

The additional requirement, if possible, is that it should only
decrypt if signed by a specific KEY ID.

Please let me know if this is possible through GPG with some shell
scripting if needed.

Thanks & Regards
Hardeep Singh