[Cryptography] The next generation secure email solution

[Joe St Sauver]

Hi,

Ralf commented:

#A user finds some website interesting and trustworthy and
#signs on. He gets a client-side X509 cert from the site 
#that is stored on his local computer (including unprotected
#private key) under a globally unique name, that can be but
#needn't be his own.

Solutions that rely on client X509 certs inevitably run into
a fairly common set of issues, a subset of which include:

-- a client cert is dropped by site in user's browser, but
   the user then changes and begins to use a different browser
   (which potentially has a different trust store and no 
   knowledge of the user's cert from the other browser)

-- user uses only one browser, but has multiple devices (which
   again implies, "How do we get the certs to those other 
   devices?)
    
-- some systems (hypothetically, systems in a university drop-in
   computer lab, a family system, systems in a public library) 
   have multiple users and may not support individual accounts
   with persistent storage for secure credentials

-- fragile as PKI support is in some products, the more certs you
   attempt to support, the more fragile that support appears to
   become (at least that's been my experience)

#Users need their certificate to log into the website that
#has issued the cert, there are no passwords any more and whoever
#*has* the unprotected private key *is* the person and can
#use the SEI. 

Do you have concerns about malware harvesting the user's private key?

#The user's local machine (the endpoint) is secure.

I think it is, as a practical matter, hard to assume that a typical
user's local machine is secure...

#Any website can create these certificates for users as long
#as SEIs are globally unique but only for local users.

So help me to understand what the user identitifier might look 
like on that client cert. Would it be a locally assigned 
"customer-ID"? cust1234 at example.com ?

And at some other site, that person might be user456 at example.org ?

#How does a user get a key?
#Read: How does the software on the user's computer fetch the
#correct recipient's public key without the user noticing what
#happens behind the scenes?
#
#The user knows the recipient's SEI, it's like an email address
#stored in the contacts list. The machine searches for the
#recipient's public key in the local key store, which contains
#all keys for SEIs that have been used before. (like ssh's known_hosts file)

Do you envision privacy issues related to the maintenance of a 
global directory of this sort?

How would the global directories maintained by individual providers
be synchronized, linked, or at least be searchable from all the other
providers?

#And if the endpoint (local machine) is the place where the private key is
#stored we will soon have another pile of SEIs becoming unusable, when laptops
#get stolen, hard drives die and local OSes become unreliable without proper
#backup procedures. This will happen.

Do you envision user discontent if their old email ceases to be accessible
when that event occurs?

#So in the end we will have a mix of working addresses and dead addresses and
#nobody can tell the difference.

If that's the case, how will users select the "right" address to use for a
given individual? 

Regards,

Joe