RE: Improving E-mail security...

[Eric Wagner <eric () intraspect com>]

Sounds interesting, though sending and receiving relays aren't always the
same.

--E

-----Original Message-----
From: Bengt Ruusunen [mailto:bengtij () hotmail com]
Sent: Tuesday, August 26, 2003 4:15 PM
To: full-disclosure () lists netsys com
Subject: [Full-disclosure] Improving E-mail security...


Hello,

As everybody knows that recent viruses spread via sending spoofed 'sender 
address'.

fex.

I am a person 'someone () someone com' and got so called 'return mail' from 
'someone () receiving organisation com' telling that mail sent by me (which I 
never sent in a first place) cannot be delivered. Obviously containg 
somekind malware as an attachment.

This kind of 'spread method' could easily stopped if the mail servers 
include some kind of fingerprint to the passing E-mail.

If the return mail (mail receiver server checks this against an private key 
or something) does not contain an fingerprint then the returned mail should 
not be delivered 'back to the sender'.

Rather clever way to counterfeit the sender address, it might double the 
infection if the bounce to the 'sender' leads to infection.

Now, what this kind of 'hardening' might need is...

- E-mail receiving server could check that 'very first original' From: line 
and if it is same than the receiver address ie. 'someone () someone com'

Perform an check to see if the 'sender identification' ie. salted public 
key, GUID or something (X-Authenticated-Guid: #0a845d299ca340087140) exists 
in mail header.

Delivery should be done only if an 'sender identification' exist and the key

matches.

Otherwise mail should be trashed to dev/null :)

Waiting for comments and succestions...

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