This whole "company key", "department key", and "personal key" business seems strangely similar to the hierarchical structure of an LDAP server. I wonder where we could store that information... :-) Just my 2¢. John E. Mayorga Jon Callas wrote:
At 03:02 AM 10/22/97 -0700, mark@unicorn.com wrote:
Thanks. I want to add that what's in 5.5 is hardly what we think is perfect. The system is designed simply to be preferable to key escrow. We have some improvements we're planning for it in the future. So you're right -- it's a short-term solution.
The current system sends out a user's personal key, with a tag to say that if I don't encrypt to the company as well, my mail will bounce. But think about this: how often do I want to send email to a particular person in a company, and ensure that only they see it? And how often do I want to send mail to a particular group inside a company? All I want is to ensure that I get a response from the company, I usually don't care who I talk to in the process.
You have it mostly right. There's a tag in a self-signature that says, "please encrypt to this other key, too." The only time you are required to encrypt to Alice's other key is if you and Alice share the same additional key (and not always even then).
So PGP's "everything private unless you choose to make it public" system seems backwards. Surely what we really need to meet these customer demands is an "everything public (within the company) unless you choose to make it private" system? That is, all mail to my department inside the company should be encrypted to a department key, shared by all members, *unless* it is confidential, in which case it should *only* be encrypted to me.
This is certainly possible with the system, and in fact easier to implement than anything else.
Here's how I see this working: when Joe Blow joins Foo-Bah Cryptosystems, he creates his own personal PGP key. He also gets a copy of the department key, which he can use to decrypt any mail which is encrypted to his department; or this decryption could be handled automatically by a department email server to ensure that individuals never have access to the department's private key. PGP then creates a public key for 'Joe Blow <joe.blow@foo-bah.com>', which would be the department key with a signed tag linking it to his personal public key. This is the tagged corporate public key which he would give out to any customers.
When a customer wishes to send email to Joe, he would use this public key. When encrypting, PGP would detect the tag and put up a dialog box pointing out that this is a corporate key and if they click on the 'confidential' button it will be encrypted to the user's personal key prior to encrypting to the corporate key (by which I mean superencryption, to avoid traffic analysis). The default would be not to superencrypt; and as a side effect this system would be compatible with any version of PGP for non-confidential mail (assuming that version understands the encryption algorithms in use).
The effect of this is that if someone wants to send email about an urgent bug and I'm out at lunch, any of my co-workers can read that mail. But if they want to send *me* mail about confidential inter-company negotiations, the co-workers could decrypt the outer layer of the message, but would be blocked by the inner layer encryption to my personal key.
As I see it, this system is simple, solves the problems which PGP claim they need to solve without creating the snooping problems Tim and others have discussed, cannot easily be adapted to GAK ('This message is to be encrypted to the FBI public key. If it is confidential, click here to superencrypt to the recipient's personal key'), and won't require a massive change to the PGP source code.
This is exactly CMR. The only thing that Business 5.5 does is automatically add the department for you, and put up the recipient dialog so it can be taken off. Congrats.
There are some obvious security issues with having the department key shared amongst the members of the department, but I don't see that they are any worse than PGP's current CMR implementation, which has already discussed the use of department keys; it's certainly better than using plaintext. There are also problems with encrypting confidential mail to multiple recipients, but they're surmountable; an easy solution, if you don't care about traffic analysis, is to only encrypt confidential mail to the personal key rather than superencrypt with the corporate key. In most cases such mail wouldn't be sent to multiple recipients anyway.
So here's how I'd see the simple system working:
A PGP CMR key would consist of
1. A corporate key; this might be company-wide, department-wide, or an individual escrowed key; this choice is a seperate key-management issue for the corporation. 2. Optionally a personal key, which could only be decrypted by the individual. 3. A signature from the corporate key linking the personal key to it and the specified User Id. 4. Optional flag to indicate which key to encrypt to by default. 5. User Id, signatures, etc
When PGP was asked to encrypt to such a key, it would check for the optional personal key. If it wasn't there, it would put up a warning box to tell the user that the message can be read by people other than the recipient. If it is, then it would put up a dialog box allowing the user to choose whether to encrypt to the corporate key or the individual key, normally defaulting to the corporate key. This system could not easily become GAK because it will only encrypt to one of the keys and not both; the FBI could create FBI CMR keys from all our public keys, but then PGP would either encrypt to the FBI and I wouldn't be able to read it, or encrypt to me and the FBI wouldn't be able to read it.
Anyone care to pick any holes?
Looks good from here. You've redesigned PGP 5.5. Thanks.
Jon
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