On Fri, 10 Jan 2020, Rich Shepard wrote:
On Thu, 9 Jan 2020, Ben Koenig wrote:
Ideally, end-to-end encryption will become an industry standard, meaning
all email clients will agree to implement it. Until that happens,
universal encryption on all platforms and devices will not be possible.
Is this end-to-end encryption implemented at the MUA level, the MTA level,
or elsewhere?
The ideal toolchain would I think be something like this.
1. End users generate a keypair (ala PGP) and publish public keys.
2. Bob uses MUA-level hooks to encrypt body of message using Carol's
public key, signing the message with his private key.
3. MUA submits message to MTA using TLS-negotiated encryption,
protecting SMTP header info in transit along with already
encrypted message body.
4. Sender MTA delivers messaage to recipient MTA using similar
TLS wire-level crypto to protect SMTP header info.
5. Recipient MTA delivers message; body remains encrypted.
6. Carol verifies her trust in Bob's public key.
7. Carol uses MUA-level hooks to decrypt Bob's message using
her private key and verifying Bob's key as the sender.
Only the in-memory version of the message is decrypted;
the on-disk message remains encrypted.
Points 3 and 4 are already in widespread use. Point 5 will always be
true is encryption is handled by the MUA.
The lack of a universally accepted key-management system hinders
points 1 and 6; I know that's where PGP is aimed, but I'd hardly call
it universally accepted.
The closest we have to an MUA standard in points 2 and 7 is S/MIME,
which is widely implemented but doesn't work with PGP, relying instead
on the same key-management techniques used to issue SSL certificates
for, e.g., web sites.
Beyond all that is the problem of data retention. It's likely that a
secure system will encourage key expiration, if for no other reason
than to keep moving away from once-secure techniques that become
insecure due to increased computing power, clever algorithm
developments, or whatever. If that's true, what do you do will all the
messages that arrived encrypted with your old key?
--
Paul Heinlein
heinl...@madboa.com
45°38' N, 122°6' W
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