Endpoint Encryption

The files I'm trying to decrypt worked fine on Friday, but today are failing with the following error:

The object was encrypted to the following public key(s):

1 unknown key(s)

If I double click on the 1 unknown key(s) I see it contact keyserver.pgp.com and then search keyserver.pgp.com but it never shows the key info.

When I check my keys, trust is set to implicit, and in the Description column it shows DH/DSS key pair for my 2 keys (only one I actually use - the one to decrypt this file). 

I went back to older files that worked fine over the last several years and they now also all give that same error.

Help!

It sounds like you have lost your old keyring, or lost the key that the file was encrypted to.
Check in your My Documents\PGP folder to see if there is a keyring that has been renamed to .old.

Have you migrated to a new computer recently?
If so, check your my documents folder on the old computer and grab the PGP folder from within My Documents. You will need to import the keys.

It is also possible that the keyring file has become corrupt. Do you have any backups of your keys/keyring? Try importing a copy from backup and using it to decrypt. 

You may also want to try exporting your private key and trying the decrypt on a different machine. This would help rule out any problems with your machine's software.

I'm able to decrypt files that I've encrypted over the years without any problem.  However - for just this one vendor - I'm unable to decrypt anything that they've ever sent (going back 7+ years) - and those files all worked just fine up until yesterday.

Could it be that it's their public key that's missing?  If they encrypt a file to send to me, they use my public key and their private.  Then to decrypt I use my private key and their public key - right? 

I do have backups from when I moved to a new PC over the summer and restored from those and still get the same results.

I did just resend them my public key in case that got messed up on their end, but I honestly may just not understand the process of file encryption correctly.

They would encrypt the file to your public key, and sign it with their private key.  Having their public key in your keyring would porovide a way to validate their signature, but not having it should not prevent decryption.

Check the key ID for the unknown key against the key ID from your public key and see if they are the same.  They should be if that is the correct key.

How do I check the ID of the unknown key?  When I right click on it it just flashes up contacting keyserver.pgp.com but nothing else. 

There are two methods for single file encryption, PGP Zip and PGP FileShare with Advanced User Mode.  In the former, you might not be able to see the Key ID.  In the latter, you should be able to right-click and go to properties.  There may be a FileShare tab which shows the access list for that file along with Key ID's.

If it was encrypted with PGP Zip, that access list will not be displayed.  I apologize, I had assumed when you said it showed an unknown key that you meant it showed "Unknown Key ID 0x00000000" (Key ID would be where the 0's are), not just "Unknown Key".