1 Dr. David MacQuigg Research Associate Autonomic Computing Laboratory System – The most important application of computer networks University of Arizona ECE December 2009

June 16, The “intractable” problems with –Spam & lost messages, $20B/year –Fraud and other serious crimes –Enabler for most malware –Threats to critical infrastructure Reasons for these problems –Ignorance –Identity fraud (can’t separate the good guys) –Investment in the status quo ($2B per year) Possible technical solutions –More of the same (IP blacklists, statistical filters) –Reputation-based systems

June 16, The problems with –Spam problem, $20B/year, “intractable” –Fraud and other serious crimes –Enabler for most malware –Threats to critical infrastructure Reasons for these problems –Ignorance (users and admins) –Identity fraud (can’t separate the good guys) –Investment in the status quo ($2B per year) Possible technical solutions –More of the same (IP blacklists, statistical filters) –Reputation-based systems

June 16, The problems with –Spam problem, $20B/year, “intractable” –Fraud and other serious crimes –Enabler for most malware –Threats to critical infrastructure Reasons for these problems –Ignorance –Identity fraud (can’t separate the good guys) –Investment in the status quo ($2B per year) Possible technical solutions –More of the same (IP blacklists, statistical filters) –Reputation-based systems

System detailed model wiki/Internet June 16, 20155

June 16, The Internet Today Our Domain Trusted Domains X ???

June 16, Textbook Model of the System Figure 9.1 Sequence of mail relays store and forward messages {Peterson & Davie, Computer Networks, 4 th ed.}

June 16, Real Mail Handling System P. Faltstrom, mail-flows-0.4, Jan 6, 2004,

June 16, D. Crocker, "Internet Mail Architecture", 2009, Function modules and the protocols used between them Relay-Level Model

June 16, Administrative-Level Model | ADMD1 | | ADMD2 | | ADMD3 | | ADMD4 | | | | | | | | | | | | | | | | | | Author | | | | | | Recipient | |. | | | | | | ^ | | V | | | | | |. | | Edge >|.Transit.+....>|-Edge >|..Consumer | | | | | | | | | Legend: === lines indicate primary (possibly indirect) transfers or roles... lines indicate supporting transfers or roles D. Crocker, "Internet Mail Architecture", 2009, Administrative Management Domains (ADMD)

June 16, The System ( a better textbook model ) |--- Sender's Network ---| |-- Recipient's Network -| / Author ==> MSA/Transmitter --> / --> Receiver/MDA ==> Recipient / Border

June 16, Shorthand Notation for System Models 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

June 16, 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

June 16, 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

June 16, 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

June 16, Secure Communications Secure communications may require any or all of: 1)authentication of the source (individual or organization identity) 2)verification of content (digital signature) 3)confidentiality of content (encryption) 4)originality (no duplicates) 5)timely delivery (no unexpected delays) 6)hidden communication (keeping an enemy unaware) Solving the problems of bulk abuse (spamming, phishing and other bulk mail scams) requires that we address items 1 and 4. To be useful in authentication, an identity must have three characteristics. It must be unique, verifiable, and suitable for accumulation of reputation.

June 16, Identities in an Session $ telnet open-mail.org open-mail.org ESMTP Sendmail /8.13.1; Wed, 30 Aug :36: HELO mailout1.phrednet.com 250 open-mail.org Hello ip068.subnet71.gci-net.com [ ], pleased to meet you MAIL FROM: Sender ok RCPT TO: 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 k7TKIBYb Message accepted for delivery QUIT open-mail.org closing connection RFC-5321 Helo Name Envelope Addresses: Return Address Recipient Addresses RFC-5322 Header Addresses: From Address Reply-To Address Network Owner Author ==> MSA/Transmitter --> / --> Receiver/MDA ==> Recipient

June 16, Authentication – The Challenge 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 transmitter addresses Or they can publish a public key Nothing else can be trusted

June 16, Authentication Summary IP-based Authentication (SPF, SenderID, CSV): Sender provides a list of authorized transmitter addresses via DNS. Can be very efficient (no data transfer) but may have a “forwarding problem” if the MDA thinks it is the Receiver. Signature-based Authentication (DKIM): Sender provides a Public Key via a DNS. Messages are signed with the related Private Key. Message content can be very secure, but an un-trusted Forwarder can replay it to millions. |--- Sender's Network ---| | Recipient's Network | / Author ==> MSA/Transmitter --> / --> Receiver/Forwarder ~~> MDA ==> Recipient / / / / Border / / / DNS

June 16, Analysis of SPF using our models Simple Forwarding | Recipient's Network | / MSA/Transmitter --> / --> Receiver/Forwarder ~~> MDA ==> Recipient / Border SPF correlates the Return Address to the Transmitter’s IP address. Forwarders are expected to re-write the Return Address. Very few forwarders are doing that. “Proselytizing” has failed. 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 by publishing “enforceable” SPF records. Senders don’t care. SPF is stuck.

June 16, 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 Both: 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.

June 16, Suggested Receiver Setup

June 16, So why isn’t it happening? Hurdles that proposed solutions have failed to 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 Users 3)Required widespread adoption of one company's method or service (Microsoft patent) 4)Changes that cause a temporary degradation in service 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)Costs to senders a) Must pay a fee, install new software, or incur some administrative cost. b) Worry about lost messages c) Need to keep track of their transmitter addresses The real reason: Reversed incentives – more spam for everyone else = more money for us

June 16, Bibliography “ System”, - cluster of articles on how the system works, security, authentication methods, etc. "Internet Mail Architecture", D. Crocker, - best relay-level model, with references to all the relevant RFC standards. Computer Networks, Peterson & Davie, 4 th ed. – good on all relevant technologies except . TCP/IP Illustrated, vol. I, The Protocols, W. Richard Stevens, Very thorough, yet readable. Good illustrations. Pro DNS and BIND, Ron Aitchison, Apress – Very readable book on the Domain Name System. "CircleID", – a "Collaborative Intelligence Hub for the Internet's Core Infrastructure & Policies" – current articles by top industry experts. Project Links – current status of our Identity and Reputation Systemhttps:// – articles and notes from early development. A short list of the most useful books and articles on and its underlying technology.

June 16, Economics of Abuse $200B annual benefit of $20B cost of abuse 100M users x ($.25/day deleting spam + $100/yr lost s) $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)