gpg 쓰시는 분계신가요? gpg encrypt 에사용자 여럿추가하려면?

http://www.glump.net/howto/gpg_intro

4.5 Encrypting for Multiple Recipients

Sometimes, you'll want to send an encrypted file to more than one person. This could create a problem, though, because no one should be sharing a private key with anyone else. You could always make a separate encrypted file for each recipient, but this can get tiring if you need to send a file to many people.

There is a better way: GPG allows you to specify a list of people who may be able to decrypt a file. GPG will then use all of those individuals' public keys to encrypt the data in such a way that any one of their private keys (and no one else's) can decrypt the data.

The syntax is straightforward. Just add more ”--recipient” options to the command line. Suppose you wanted to encrypt the same message as in Subsection 4.3.2 above, but wanted to send the message so that both you and I could decrypt it later. You would type the following at the command prompt:

gpg --armor --recipient "Brendan Kidwell"
--recipient "YOUR-NAME"
--output "message to brendan.txt.asc"
--encrypt "message to brendan.txt"

and then copy the output file into an email message as before.

Sending encrypted email this way can make it easier to manage your saved correspondence. Normally when you send plaintext email, a copy of the sent message is saved somewhere in your email software (unless you specified that you don't want to save copies.) You can always go back and review your sent email to recall what was said. If you specify your target and yourself as recipients when you prepare an encrypted message, then you can go back and review it in your sent email collection whenever you need to, with only the added step that you need to decrypt it before you view it. You needn't save a separate plaintext copy of the message, nor do you need to make another copy encrypted for yourself.

Specifying several recipients does not adversely affect the size of the encrypted data. I tried encrypting a large (~8MB) compressed binary file for one and then two recipients. The difference in the size of the output was only a few hundred bytes.