Independent Message Channels

So far in the development of Ecca we have eliminated passwords,
created anonymous accounts at web sites. We created a protocol for
anonymous messaging at at dating site, so strong, the site could not
read the messages, even if it wanted to.

To top it of, we created a way to keep the dating site honest by
detecting when a site becomes dishonest. It prevents the site from
trying to wriggle it in a position where it could read and manipulate
the messages undetected. It may try but it will be detected and the
whole world can learn about it.

In our dating site example, a single site controlled the namespace
(the nicknames it signs) and it controlled message delivery.

We are going to separate naming and delivery.

If you wanted to send a message to user X at site Y, you’d
ask the registry for the certificate of {site Y, User X}. It would
return the certificate it had for that combination of sitename and
nickname. You’ld encrypt your message to User X with the public key
inside the certificate and drop off the encrypted data at Site Y.

It may sound complicated but there is an old-school (non crypto)
version where you drop off messages for User X at Site Y. You’ll
recognise immediately: UserX@SiteY.com. It’s a plain old email
address. And that explains why it’s called an address. It’s the
place where you have to deliver it.

With cryptography we can do better. We will separate naming and delivery.

The dating site controls the naming of the users. The dater controls where she’ll
want to receive the messages. She will not use the message service of the dating site. Here is how:

Our dater opens a mail delivery box somewhere. This is an entirely new
concept. It’s the electronic form of a P.O.-box. It is just a system
where anyone can deliver any ‘message’ to our dater. The box just
stores the messages until our dater comes to pick them up.

Just like a P.O-box has an address without a name of whom it
belongs. For example: Box 25, post office Rotterdam
Centre”. Eelectronic PO-boxes have addresses without names too. It
could be as simple as a URL: “https://pobox.example.com/dropoff/123456789".

Independent Message Delivery Independent Message Delivery

Assume our dater has opened this address anonymously, with the methods
from chapter 2. “Anonymous logins at web sites”. For this she uses a
new and different certificate. The PO-box provider knows her as “anon-4321”

After opening the account she makes a note stating her delivery
address. She signs the note with the private key of her ms. Janet
account. Then she sends the signed note to the registry.

The registry validates the signature on the note. When the signature
is valid, the registry adds it to its database. Ready for everyone to
ask.

When mr Bob wants to write a message to ms Janet, he performs all
certificate validation steps a as in the previous chapter. He also
asks the registry for ms Janets delivery address. Instead of handing
the message to the dating site for delivery, he drops it off at the
delivery address from the note. Eg, the dropoff address.

A bit later, ms Janet feels lucky and checks the po-box site. She logs
in with her anon-4321 account and she gets the encrypted message from
mr Bob. She decrypts the data with he Janet-account. In it is the
message, signed by mr. Bob. It also contains a return address, also
signed by mr. Bob. She only needs to perform the certificate
validations to check that the dating site is honest. (Otherwise, it
could be the dating site impersonating mr. Bob.)

It sounds difficult but remember, the computers do all the hard work for us (people).