We have this topology in our company:

Intranet: DC + self-certificate. John → Paul.

A new rule says that each document being sent by Outlook should be encrypted. We decided using PGP. We already have a certificate (self-signed).

The problem is this:

  1. John and Paul install the certificate.
  2. John encrypts using the public key and sends the PGP file to Paul.
  3. Paul needs the private key in order to open it (+ verify it).

But wait! The private key is private and Paul should not have access to it. So how will Paul decrpyt John’s data ?

Even if Yoko gets the file attached to the email from John - she SHOULD NOT be able to open it. Only Paul. We NEED to send encrypted files from John to Paul, not only securing SSL - but the FILE itself. (The documents have very sensitive data.)

What am I missing?

(p.s. I know I can install PGP as an add-on into Outlook, but I'm trying to understand the concept of Paul not being able to have the private key.)

2 Answers 2


PKI works on the premise that every sender and every receiver has their own key pair, one key for the whole organization doesn't work. John will encrypt the data using Paul's public key and send it to Paul, who will use his private key to decrypt the data. He knows it is authentically from John because it will be signed using John's private key, and he can verify that using John's public key.

I recommend you read up on Public Key Infrastructure to understand the topic.

IMHO, you are using PGP for the wrong reasons. Internally encrypting email using PGP has little value if you are enforcing SSL/TLS connections and encrypting data at rest on all systems using tools like bitlocker. What PGP is useful is to encrypt email between your company and other endpoints where you cannot enforce an encryption regime.

  • why do you think I don't know this topic :-) ? I asked a question showing I do understand it. but didn't know how it will work in a multi user environment. I thought something about global private key which is used only for decypher. and of course global public key. still, your solution make sense.
    – Royi Namir
    Oct 30, 2012 at 11:00
  • Just to be sure , our administrator CAN supply each worker a certificate without buying anything...right ? ( again , we work in intranet). and ofcourse he has to backup each certificate in case when formatting john's computer for example ....right ?
    – Royi Namir
    Oct 30, 2012 at 11:01
  • @RoyiNamir, I think you understand how Public Key Cryptography works, but not Public Key Infrastructure. There is a difference, and that's why I suggested the link. You shouldn't need to spend any extra money to achieve this if it is all internal, but see my last paragraph as top why you probably don't need it.
    – GdD
    Oct 30, 2012 at 11:15
  • I'm working in an ensurance company. even if yoko gets the file attached to the email from john - she SHOULD NOT be able to open it. only paul. we NEED to send encrypted files from john to paul , not only securing SSL - but the FILE itself. ( the documents have very sensitive data)......now after my answer , am I still wrong ? please reply :-)
    – Royi Namir
    Oct 30, 2012 at 11:20
  • If that is your requirement than PGP certainly will do the trick. Every user account that needs to send or receive encrypted email will need its own key pair. For completeness it may be worth editing your question with that last information.
    – GdD
    Oct 30, 2012 at 11:25

You just need to rephrase your statements to get an answer:

John encrypt using Paul's public key. and send the pgp file to Paul.

Paul's public key is public and everyone can access it.

Paul need the private key in order to open it ( +verify it).

Paul's private key is private ! and only Paul can access it.

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