Transcript Email Abuse - University of Arizona

Autonomic Trust System
– Verify Identity and Assess Reputation
Dr. David MacQuigg
Research Associate
Autonomic Computing Laboratory
University of Arizona
ECE 509
November 2008
1
• The Problem with Trust on the Internet
– Spam problem, $20B/year, “intractable”
– Fraud and other serious crimes
– Non-technical factors are critical
• Modeling of Mail Handling Systems
– Actors, Agents, Terminology
– Roles and Responsibilites
• Trust = Identity + Reputation
• Identity (Authentication)
– IP-based (CSV, SPF, SenderID)
– Signatures (DKIM)
• Reputation
– Reputation/Accreditation Systems
– Registry of Internet Transmitters
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Economics of Email Abuse
$200B annual benefit of email
$20B cost of abuse
100M users x ($.25/day deleting spam + $100/yr lost emails)
$2B benefit to anti-spam industry
100 companies x $20M/yr
$0.2B benefit to spammers
10K spammers x $20K/yr
$0.02B cost of an effective authentication/reputation system
10M users x $2/yr
100K companies x $200/yr (90% internal, 10% external services)
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Textbook Model of a Mail Handling System
Figure 9.1 Sequence of mail relays store and forward email messages
{Peterson & Davie, Computer Networks, 4th ed.}
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Real Mail Handling System
P. Faltstrom, mail-flows-0.4, Jan 6, 2004, http://www.ripe.net/ripe/meetings/ripe-47/mailflows.pdf
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Relay-Level Model
Function Modules and the
Protocols used between them
D. Crocker, "Internet Mail Architecture", 2008,
http://tools.ietf.org/html/draft-crocker-email-arch-10
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Administrative-Level Model
+-------+
+-------+
+-------+
| ADMD1 |
| ADMD3 |
| ADMD4 |
| ----- |
| ----- |
| ----- |
|
|
+---------------------->|
|
|
|
| User |
|
|-Edge--+--->|-User |
| |
|
|
+---------+
+--->|
|
|
|
| V
|
|
| ADMD2 |
|
+-------+
+-------+
| Edge--+---+
| ----- |
|
|
|
|
|
|
|
+-------+
+----|-Transit-+---+
|
|
+---------+
D. Crocker, "Internet Mail Architecture", 2008,
http://tools.ietf.org/html/draft-crocker-email-arch-10
Administrative Management
Domains (ADMD)
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The Internet Today
3
The Swamp
Trusted Forwarders
Our Domain
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Typical Mail Handling System ( a better textbook model )
|--- Sender's Network ---|
|-- Recipient's Network -|
/
Author ==> MSA/Transmitter --> / --> Receiver/MDA ==> Recipient
/
Border
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Proposed Model for Mail Handling Systems
Simple Setup with four Actors
|--- Sender's Network ---|
|-- Recipient's Network -|
/
Author ==> MSA/Transmitter --> / --> Receiver/MDA ==> Recipient
/
Border
Actors, Roles and Notation
Actors include Users and Agents.
Agents may play more than one role, but no role has more than one Actor.
Typical roles include Transmitting, Receiving, Forwarding, and Delivery.
A Border occurs when there is no prior relationship between Agents.
--> Direction of mail flow (no statement as to relationship)
~~> Indirect relationship (e.g. both directly related to Recipient)
==> Direct relationship between Actors (e.g. a contract)
A/B Roles A and B both played by the same Actor
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Other Common Setups
Simple Forwarding is quite common
|-------- Recipient's Network ---------|
/
--> / --> Receiver/Forwarder ~~> MDA ==> Recipient
/
Border
Chain Forwarding should be discouraged
|------------ Recipient's Network ------------|
/
--> / --> Receiver ~~> Forwarder(s) ~~> MDA ==> Recipient
/
Border
Open Forwarding must be banned
/
/
|-- Recipient's Network -|
--> / --> Forwarder --> / --> Receiver/MDA ==> Recipient
/
/
Border
Border
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Roles and Responsibilities
Author
- Originate messages
- Provide a password or other means of authentication
MSA - Mail Submission Agent
- Authenticate the Author
- Manage Author accounts
Transmitter
- Spam Prevention
- rate limits, content analysis, alerts
- respond to spam reports
- maintain reputation
- Authentication
- RFC compliance
- IP authorization (SPF, SID, CSV, ...)
- signatures & key management (DKIM ...)
Receiver
- Block DoS
- Authenticate Sender
- HELO, Return Address, Headers, Signature
- reject forgeries
- Assess reputation
- whitelists
- Filter spam
- Add authentication headers
- Manage Recipient accounts/options
- whitelisting, blacklisting, filtering, blocking, forwarding
- Process spam reports
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Roles and Responsibilities (continued)
Forwarder
- Authenticate upstream Agent
- Set up forwarding to downstream Agent
- check RFC compliance
- set up authentication records
- submit forwarding request, wait for approval
- Manage Recipient accounts
- maintain database of forwarding addresses
- suspend account when a message is rejected
- communicate w Recipient re "
"
- Maintain reputation as a trusted Forwarder
- certifications
MDA - Mail Delivery Agent
- Authenticate upstream Agent
- Sort and store messages
- Provide access for Recipients
- POP3, IMAP, Webmail
- Manage Recipient accounts/options
- Relay spam reports to Receiver (or don't accept them)
Recipient
- Set up accounts with each Agent
- Select options in each account
- Report spam to Receiver
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Identity – Authenticating the Sender
SMTP makes Forgery Easy
Forger -------> /
/
Author ==> MSA/Transmitter --> / --> Receiver/MDA ==> Recipient
/
/
/
/
Border
/
/
/
-- Secure Channel --
TCP makes IP addresses (relatively) secure
The source address is real, but it may be only a zombie!
DNS offers a (relatively) secure channel
Domain owners can publish their authorized addresses
Or they can publish a public key
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Authentication Methods
Author ==> MSA/Transmitter --> / --> Receiver/MDA ==> Recipient
/
/
/
/
Border
/
/
/
-- Secure Channel --
IP-based Authentication (SPF, SenderID, CSV):
Sender provides a list of authorized transmitter addresses.
Can be very efficient (no data transfer).
Signature-based Authentication (DKIM):
Sender provides a Public Key via a secure channel.
Messages are signed with the related Private Key.
End-to-end protocol can be very secure,
even with an un-trusted Forwarder in the middle.
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Reputation – the other half of trust
Millions of legitimate senders are simply unknown
Aggregation of data is essential
Ground Up: Gossip
Top Down: Proprietary Systems
Registry of Internet Transmitters
Some legitimate senders are not qualified to operate a transmitter
Make outsourcing the Transmitter role easy.
Accountability is essential – no excuses.
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So why isn’t it happening?
Hurdles that trust systems must avoid or overcome,
in order of decreasing severity:
1) Required simultaneous upgrades in software or setup (Flag Day)
2) Required widespread adoption by Agents before any benefit is realized by Recipients
(By June 30th, all senders will ...)
3) Required widespread adoption of one company's method or service (Microsoft patent)
4) Changes that cause a temporary degradation in service
( loss of mail due to misconfigurations on the Receiver side )
5) Changes in current practices
a) A well-established and standards-compliant practice.
b) A widespread but non-standardized practice. ("Misuse" of Return Address)
c) A widespread but non-compliant practice. (bad HELO name)
d) An already unacceptable practice. (open relays)
6) Lack of motivation
a) Can’t keep track of all their transmitter addresses
b) Reversed incentives – more spam = more money
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Suggested Receiver Setup
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Analysis of SPF using our models
Simple Forwarding
|-------- Recipient's Network ---------|
/
--> / --> Receiver/Forwarder ~~> MDA ==> Recipient
/
Border
SPF correlates the Return Address to the incoming IP address.
Forwarders are expected to re-write the Return Address.
Very few forwarders are doing that.
A misconfigured MDA sees the forwarded message as forgery.
The message is quarantined, and possibly lost.
Senders are avoiding the loss by publishing “neutral” SPF
records.
Forwarders will not change until senders demand it.
SPF is stuck.
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Bibliography
A short list of the most useful books and articles on the technology underlying email.
• TCP/IP Illustrated, vol. I, The Protocols, W. Richard Stevens, 1994. Very
thorough, yet readable. Good illustrations.
• Computer Networks, Peterson & Davie, 4th ed. – good on all relevant
technologies except email.
• "Internet Mail Architecture", D. Crocker, http://www.ietf.org/internet-drafts/draftcrocker-email-arch-11.txt (work in progress) - best overview with references to all
the relevant RFC standards.
• Pro DNS and BIND, Ron Aitchison, Apress 2005. – Very readable book on the
Domain Name System.
• "CircleID", http://www.circleid.com – a "Collaborative Intelligence Hub for the
Internet's Core Infrastructure & Policies" – current articles by top industry experts.
Project Links
• https://www.open-mail.org – current status of our Identity and Reputation System
• http://purl.net/macquigg/email – articles and notes from early development.
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Identities in an Email Session
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$ telnet open-mail.org 25
220 open-mail.org ESMTP Sendmail 8.13.1/8.13.1; Wed, 30 Aug 2006 07:36:42 -0400
HELO mailout1.phrednet.com
250 open-mail.org Hello ip068.subnet71.gci-net.com [216.183.71.68], pleased to meet you
MAIL FROM:<[email protected]>
6 Network Owner
250 2.1.0 <[email protected]>... Sender ok
RCPT TO:<[email protected]>
250 2.1.5 <[email protected]>... Recipient ok
DATA
354 Enter mail, end with "." on a line by itself
From: Dave\r\nTo: Test Recipient\r\nSubject: SPAM SPAM SPAM\r\n\r\nThis is message 1 from our test
script.\r\n.\r\n
250 2.0.0 k7TKIBYb024731 Message accepted for delivery
QUIT
221 2.0.0 open-mail.org closing connection
RFC-2821
1 Helo Name
Envelope Addresses:
2
Return Address
Recipient Addresses
3
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RFC-2822
Header Addresses:
From Address
4
Reply-To Address
5
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