this is a request for this list to be digitally
signed by the list processor.
to all list members. if after reading this post
you would like the list processor to digitally
sign all posts please say so (and tell the list
owner) so that the level of interest can be
i'm making this request because i need a way to
positively id the messages from this list. i'm
spending way too much of my time culling spam from
my real email even though i'm employing the latest
spam filtering tools. please give me the one
simple tool i know of that will allow me to
positively differentiate the mail from this list
from all others - a digital signature.
signing all list messages won't be detrimental to
list recipients not interested. it will however
allow folks wishing to implement anti-spam
measures around digital signatures to do so.
mailing lists often require that recipients
confirm their email address as an anti-spam
measure for the list. please help list recipients
implement their own anti-spam measures by allowing
the list messages to be positively identified.
to be clear, this is a limited scope spam
solution, but it works. and it will continue to
work provided the underlying cryptography is sound
(unlike many other anti-spam technologies that are
simply clever hacks in an escalating spam/anti-
spam arms race).
some folks say that there will be no spam solution
as long as email is free. i say there will be no
spam solution as long as you expect anyone to be
able to send email to you without first proving
they are not a spammer.
part of finding a solution is to revision what
email is. i argue that email can no longer be a
method of unfettered *initial* contact. once that
is accepted then this solution doesn't seem
painful. i suspect that there won't be a solution
until email is seen from this perspective. as
noted above, mailing lists are essentially
adopting this perspective (to better manage spam
on the list side), it would be helpful if they
took an additional small step that would enable
list recipients to better manage spam on their end
there's no need for a larger web of trust other
than one that is personally maintained when using
digital signatures to defend against the onslaught
of spam. your personal web of trust (a.k.a. your
keyring) is your unspoofable anti-spam whitelist.
this is where the revisioning of email occurs.
instead of email being the way you initially make
contact with an entity, with digital signatures it
can serve as a reliable communications channel
*once* contact has been established.
my intention is to implement a procmail recipe at
the mail server level. the procmail recipe will
be used to check incoming mail for whitelisted
digital signatures that have been uploaded from
each individual user.
mailing lists could use the same recipe, no
messages would be handed over to the listserv
software unless it was signed by a whitelisted
signature. again, this won't stop machines from
being compromised but as soon as a machine is
compromised that entity will be *immediately*
notified by their peers. in the case of a mailing
list *many* people will suddenly know who's
compromised and the list can even have a mechanism
that allows a whitelisted key to be removed once
it becomes compromised. this would also serve the
dual function of indirectly alerting the owner of
the compromised host since they will investigate
why they are no longer receiving list traffic.
regarding whether to utilize inline or mime GPG, i
say use either. the preferred solution will self-
select over time. it is possible to create a
procmail recipe that can handle both methods.
Two key benefits of this anti-spam technology:
1. it works and will likely continue to work
beyond the foreseeable future
2. it can be implemented without the consensus,
from the bottom up
below are my responses to posts in a few mailing
list threads regarding digital signatures and
spam. please read my responses as they will
likely answer many of the questions that may
result from reading what i wrote above. apologies
to the folks whose comments i'm replying to for
not referencing their names (i didn't have the
looking forward to feedback.
spam is something we can eliminate by
changing our personal behaviors and expectations
and cooperating. and it can happen gradually.
thread: ietf - proposal for built-in spam burden
& email privacy protection -----
2. Except for senders in a whitelist (e.g.,
list mail), I bounce to the sender any email
that is NOT encrypted with my public-key,
providing my public-key and instructions for the
sender to resubmit the message properly
Anything at all that generates a bounce message
on a mass-produced mailing acts as a "damage
amplifier" from the basic internet backbone's
point of view -- at least doubling the associated
automated traffic and wasted/misused resources.
These days such a bounce is especially fruitless,
as all viruses and quite a lot of SPAM have forged
headers that the stupid bounce agents cannot or do
This is pet peeve of mine as it is -- I got (and
continue to get) more bounce messages from mydoom
reporting that mail "from me" is contaminated than
I do copies of the virus itself. No virus for two
years now hasn't forged mail headers -- the From
field is totally irrelevant in all current viruses-
- yet all the AV programs in the world think they
are doing you a favor. NOT.
Now imagine that sort of stupidity scaled out so
that every MTA in the world is checking esigs and
bouncing improperly signed mail. Imagine the
loops created when a legacy mailer or improperly
configured mailer bounces the bounce messages back
to the bouncer, to be bounced again. Nightmarish.
solution - don't auto-respond, give out a keyword
with your email address, this will allow initial
contact to be more easily plucked from the sea of
spam - in the long run as more people digitally
sign email spam will become even less profitable
because there will be even fewer responses - we'll
never know what's possible if we don't try
encrypting for each of the list recipients is too
much of a burden for the list
solution - don't encrypt, only digitally sign -
not a burden
Don't get me wrong: encouraging people to use pgp
is a good idea, but making it a requirement before
accepting it is a policy decision that the end
user should be making, not the list.
solution - by only digitally signing it is
completely up to the end user to decide whether or
not to add this tool to their anti-spam toolbox
Your proposal is in line with some existing ones,
at least one of which response to the seriously
problematic key management issue.
solution - non-local, centralized key management
is a huge problem, but key management isn't a
problem if the only important keys are your
personal ones and if you don't expect to be able
to instantaneously have access to anyone's public
key via a keyserver - keyservers aren't necessary
for folks who exchange email with primarily a
small group of people
I'm not saying to reject non esig mails, but to
held them for approval by moderators... If you
want your post to go through quickly, sign it...
It would be a worthwhile incentive.
sounds like a great idea, but this is in addition
to and isn't required for what i'm suggesting
Also note, there is an addition burden placed on
end users who rely on receiving encrypted email in
your proposal. Under your scheme, a user has to
go through the trouble of decrypting the message
just to see if it is spam or not. This eliminates
almost all forms of automated spam mitigation
except those related to the low-level SMTP, DNS or
other new authentication/authorization techniques.
reminds me that signing and not encrypting still
allows bayesian filters to continue to be useful
Unfortunately, requiring that they have a
published public-key *is* a burden to the average
user. J. Random Luser just wants to sit down at
his PC, boot up Winders, bring out Lookout, and
forward a garish HTMLified email full of stale
jokes to his buddies, complete with pictures, and
he wants it to go through, without a hitch, right
now. He thinks public keys are the ones hanging
on the gas station wall, for the bathroom. He
thinks crypto is someone from Superman's home
planet. He thinks the IETF is them guys whut
raided David Koresh. He has no clue what the ASRG
is, but he thinks it sounds dirty.
again, no need for keyservers for folks that are
exchanging email within a small group of people.
also, let's stop trying to allow email to continue
to be what it has evolved into, let those folks
that want email to stay the way it is keep it that
way, let's create a spam-free email environment
that works and satisfies *us*, i suspect that if
this is witnessed folks will eventually start
thinking of email differently as their personal
spam pain tolerances are exceeded.
Make it worth their while, by coming up with
infrastructure such that they won't get any spam
if they have a public key, and MAYBE they'll
bother doing it, IF the ISP will hold their hands
every step of the way (and not charge them too
much, including for issuing new keypairs when they
let the private ones slip out too much). Of
course, this means that all their equally
technically-enlightened friends have to know how
to USE his public key....
solution - accept that it will be a gradual
process, let's just start with mailing lists
signing all messages that get sent to list
recipients - that's easy
This sounds very much like the use of extra
headerz, or a password on the subject line, but on
steroids. In the end, possibly useful, IF you can
get everybody aboard, but they won't go until
everybody ELSE is already on board, and meanwhile
it's a pain in the proverbial posterior to
everyone who wants to communicate with the people
for me it is *less* pain than what i'm
experiencing dealing with my current spam load,
and digital signatures can be ignored if you don't
want to verify them - also, if someone tells you
that they are receiving so much spam that you will
have to sign all email you send to them, are you
going to tell them they are causing you too much
pain? heck, just pick the phone up and call them
Second, even if the above weren't a problem, one
still has the problem that a virus infected user
will still be sending messages, just like everyone
this will still be a problem but with a digital
signature solution in place infected computers
will be identifiable and probably immediately
disinfected, folks will become hyper-aware of
allowing their machines to become compromised if
suddenly they are unable to exchange email with
their small and *important* group of people
because their public key became blacklisted by
these same folks - the very nature of digital
signatures positively identifies infected
There is no scheme in which the rules can't be
broken by someone intent on breaking them. The
only path is to detect them, and prosecute them.
In the case of spam, detection is easy, but not
automatic. Prosecution is now possible. Its
still a whack-a-mole game. It won't end unless you
can get past the virus infection to the virus
operator, and hopefully, there aren't really too
many virus operators. Of course, we aren't
stopping spam either in a very real sense, but
rather abusers who are annoying and mailbombing
people. But by my count of my inbox, if you stop
those people, I can certainly handle the rest
which amounts to maybe 1% of my current junk mail.
there's no known way to crack GPG, widespread
adoption of digital signatures against spam will
either help bring spam to and end or tell us what
NSA might already know ;) - let's put those
spammers to work! also, prosecutions by a central
authority won't be necessary, peers will do the
prosecuting by rejecting email from compromised
systems, the owner of the infected system will be
de facto "punished" because communications with
their peers will end until they clean their system
(or stop spamming).
The "for pay" idea is just another scam from
the people who would love to get a percentage of
the pay. While I'm sure Microsoft and others would
just love to get a cut of this (I know I would),
it doesn't do anything to stop spam, and if
implemented, would simply (and wrongly) charge
users whose computers were virus infected.
Wrongly? I'm not so sure. Something ought to be
done to stop the Typhoid Marys of the Internet.
Putting them on notice that they WILL be held
responsible for spreading the infection, or its
effects, just MIGHT result in them FINALLY taking
some responsibility for their "computer hygiene".
Sure, there will have to be several well
publicized example cases before most folk will sit
up and take notice, but in the long run, it might
i agree, trying to impose a burden
(computationally or monetarily) on spammers will
not work IMHO. i will leave it to others to
explain this in more detail. and to repeat,
prosecutions by a central authority won't be
necessary, peers will do the prosecuting by
rejecting email from compromised systems, the
owner of the infected system will be de facto
"punished" because communications with their peers
will end until they clean their system (or stop
So even discussing adding a silly thing like
mandatory esigs and encryption as an antispam
measure is a waste of time, except possibly on a
local basis. If I set up a small mailing list (or
generalized group of individuals) and all of its
members agree to do this, there is little
"evolutionary pressure" for spammers to detect and
foil our scheme and we will be "immune" (at the
cost of a fair amount of extra work). If
everybody does it and the automated tools for
doing it without so much work are widely
disbursed, they will develop countermeasures in no
time at all and we'll lose our immunity.
please explain how spammers will evolve past the
public key encryption technology used in digital
signatures? as noted earlier machine compromises
will still occur but they will be able to be dealt
with because peers of the compromised machine will
immediately identify and neutralize the problem by
ending communication (by blacklisting the
compromised key). suddenly the owner of the
compromised machine hears silence.
Automated text analysis will never be perfect,
because even human text analysis for
interest/disinterest (secretaries) aren't perfect.
But it can help sort things. I hand filter about
1500 messages a day. I get about 3500 over the
weekend. Monday's filtering doesn't take me any
longer than tuesdays filtering.
unfortunately the approach you describe could
likely be your undoing in the long run as spammers
ratchet up the volume to the point were it *will*
take you a long time using this approach. this is
why even with 99.9% accurate bayesian filtering,
all spammers need to do is ratchet up the volume
to get more spam through the 0.1% error rate of
the bayesian filter.
Then using the IETF list as an example, you
would need the entire list of recipients and their
public keys, and you would need to send a message
either directly to each of them, one by one, or
send a single message with a session key for each
recipient (thousands). This isn't going to work.
Let's not mix apples with speedboats. These are
some options with the proposal:
#1: no encryption is used either way, the list
address is in a whitelist for each recipient.
#2: each recipient can only send encrypted msgs
(possibly, also signed) to the list, with the
list's key, for distribution. The listserver
verifies and resends the messages in plain text,
where #1 applies for each recipient.
#3: the list receives messages as in #2 but the
listserver sends the msgs as encrypted mail to
each recipient, with each recipient's key.
#4 (my preferred) the member send a message to
the list with his digital signature. The list
checks the digital signature (from keyserver or
from a member database) and post the message if
signature is valid. If the signature is not valid,
the message is held for approval. But yes this
scheme does not offer much more than restrict
posting to list members only, which the IETF had
to do last year(?).
if the list server signs each message that then
allows recipients to positively identify mail from
the list. this is *HUGE*. if i have an email
account that only receives mail from mailing lists
that sign all messages then i can dump all
incoming non-whitelisted digitally signed email at
the server and *know* that all my email is legit.
thread: ietf - how not to filter spam -----
first, there is an increasingly heated debate
between folks who want to sign the message (TEOS,
DomainKeys), versus others who want to secure the
channel between sender and receiver (RMX, LMAP,
What does it matter what the resolution is?
Neither solution eliminates the spam channel, and
solves the problem, as information theory shows.
Its just a silly debate over two schemes to thread
a needle that can't be threaded.
think of spam as a river passing through multiple
channels, let's find a channel we can change.
folks talk about spammers taking advantage of
email protocols. another angle is to say that
spammers take advantage of people's behavior.
it's much easier to change my personal behavior
and expectations with regard to email than it is
for me to change an established internet protocol.
so stop thinking about eliminating the ability to
send spam and focus on *absolutely* identifying
real email. spam will dry up as people are able
to absolutely identify real email.
That sounds like the old "authentication solves
spam" hope. It was wrong before SMTP-AUTH and it
is still wrong.
Guess what, it is impossible to "solve" spam the
same way it is impossible to "solve" burglary. At
least with authentication you get to have
whitelists that work. If you get a message with my
email address in the "from" line it could be from
anyone. If it is signed with my PGP key you know
it came from me personally or someone went through
a LOT of trouble to get access to my private key
and the key phrase.
The usefulness of authentication could be further
extended by building a web of trust where people
vouch for the fact that others aren't spammers.
Obviously spammers will slip through from time to
time, but anyone who spams or keeps vouching for
spammers will be removed from the web of trust.
But even if this part doesn't work authentication
is still useful.
thread: tidbits - digital signatures in tidbits --
As I said earlier, I don't see the point of doing
it for this list, but the mechanism itself isn't
so easily spoofed. Think of it as an address
based whitelist with addresses that can't be
forged. A spammer wouldn't be able to get his own
public key on the whitelist, and can't pretend to
be someone else because he doesn't have the
corresponding private key. I personally wouldn't
use such a system, since the Bayesian spam filter
I use (bogofilter) works well enough, but people
that are more annoyed with spam than I get might
find such a system attractive.
exactly, my bayesian filter (POPFile) works great,
but i get so much spam that the 1% of my email
that doesn't get classified correctly is causing
me too much pain.
Then you have to start allowing attachments on
the list...not a great idea.
Not necessarily. This should work as text only
with PGP 8.
Attachment converted: HHBV HD:PGP.sig (pgDS/----
Obviously, it does not work except by allowing
attachments... and it's hard to believe that
TidBITS Talk would ever come to that.
no, digital signatures can be inline, the mime
attachment method is more robust but not required.
so tidbits can be signed without mime
attachments. FWIW, most email clients do support
the mime method.
There are plenty of uses for digital
signatures, but I don't think approving mailing
list postings is likely to be one of them any time
Agreed. Remember the messages that slipped
through were approved by Adam because of poor html
formatting, except one that forged his email. If
he used digital signatures most of those messages
still would've been signed, and just like Habeas
headers, if you're spam filter auto-whitelists
signed messages they would come through.
exactly, if the list is signed spam can still get
through. what the signature does is allow the
mailing list traffic to be positively identified
amidst the personal flood of spam many folks
receive. just like we help list maintainers out
by taking extra steps to allow posting,
maintainers could help us out by signing all list
messages. dealing with spam requires cooperation.
I think people should sign all of their
messages. That will have several effects: - Peole
will get suspicious if a message isn't signed,
making forging mesages harder.
How do you handle email from a kiosk, or a cell
phone, or someone else's computer? There are too
many instances in the real world where this
happens. It's one of the benefits of IMAP..you
don't HAVE to be on any particlular computer to
get your email.
by locating signature verification at the mail
server level. create a procmail recipe that will
automatically tag all signed email as to whether
or not the signature exists in the personal
whitelist that has been uploaded to the server.
I do think we're getting off topic but -- any
modern approach to the spam problem must take into
account the fact that at any given time the
Internet contains millions of insecure computers
that can be taken over by viruses and used as
zombies to, among other things, send spam. If
digital signatures were actually used in some
standardized way, it would be trivial for the
virus to grab it and sign its messages.
again, digital signatures as an anti-spam
technology will be effective for folks who don't
*need* to be able to be contacted by anyone on the
internet prior to them verifying they're not a
spammer. folks that need to be this accessible
need to either modify this requirement, continue
to rely on statistical spam filtering tools, solve
the key distribution problem, and/or work to
change established internet protocols.
This assumes that you already have all the keys
of potential correspondents in your keyring,
which makes this just another form of
whitelisting, albeit a cryptographically secured
one. The shortcomings of whitelisting systems are
well described here and elsewhere, but basically
you'll have to read all your (signed) spam just to
make sure there isn't a message there from someone
you haven't whitelisted yet. Remember, too, that
public keys really should expire, so you would
need a method for keeping your whitelist (keyring)
up to date. If you try to automate the whitelist,
you open the door to spammers again.
you are assuming the receipt of email from a large
previous unknown group of entities. if this is
you then you won't benefit from digital signatures
adopted on a small scale. but if you are one of
the many folks who only receives email from a
small group of people then digital signatures
ensure that you will never miss one of their
I'm a big proponent of cryptographic signatures;
they just aren't the Final Ultimate Solution to
digital signatures don't do anything whatsoever to
end spam - they allow spam to be sent to > /dev/null
Whitelists work great for those corresponding to
just a few people. But they simply aren't pratical
for participation in mail lists.
at the very least a digitally signed list (by the
list software/moderator) allows list recipients to
identify list traffic. i do have my doubts about
how impractical it would be for the list
software/moderator to check for digital signatures
prior to posting messages from list members.
think gradual implementation, let go of the notion
of all members signing their posts, although they
might, and for every list member that does sign
that's one less post to be analyzed to see if it's
Whitelists work great for those corresponding
to just a few people. But they simply aren't
pratical for participation in mail lists.
Sure they are. You are missing the whole point of
how digital signatures would/should be
implemented in a discussion list environment.
It's not the end user who needs to verify the
signature, it's the list processor.
I subscribe to a list. As part of that process I
provide the public half of my key. Any message I
submit to the list is signed by me using my
private key. The list manager software then
verifies my signature and passes the verified
message on to the list or to the list moderator.
This ensure that only messages written by bonefide
members of the list get past on to the members of
The whole point is not to ensure that messages
coming from the list are signed but to ensure that
messages submitted to the list are signed.
This also obviates the need for the list to
support attachments and makes pgp/mime a BETTER
alternative to inline signing. The list processor
receives the messages, verifies the signature and
strips the signature. I, as a subscriber to the
list, never see the signature.
Maybe, the list processor itself signs the
messages it sends out. In which case I only need
to have the one key (the public key for the list)
in my keychain.
well said. i differ only in that i would start by
having the list processor sign the list (what i
perceive to be a simpler yet positive step) rather
than trying to get list members to sign in order
If we stop all counterspam measures by pointing
out that they aren't the Final Ultimate Solution
To Spam (TM), the situation will never improve.