Accredited DomainKeys: Accredited DomainKeys: A Service Architecture for A Service Architecture for Improved Email ValidationImproved Email Validation
Michael GoodrichMichael Goodrich Roberto TamassiaRoberto Tamassia Danfeng Yao Danfeng YaoUC Irvine UC Irvine Brown UniversityBrown University
Work principally supported by IAM RegistryWork principally supported by IAM RegistryAdditional funding from NSFAdditional funding from NSF
OverviewOverview
DomainKeys signs DomainKeys signs outgoing messages using public-key cryptography (Delany 04)– Did the sender actually send this email?
Accredited DomainKeys provides assurance of sender’s public key and evidence of sender domain’s trustworthiness– Is the sender of this email trustworthy?
Two approaches of implementing Accredited DomainKeys are presented
Send and Receive in DomainKeysSend and Receive in DomainKeys
Example.net Name Server
Example.net MTA
Yahoo.com MTA
Sign mail
Private key
Public keyQuery for public key
Verify signature
DomainKey-Signature: a=rsa-sha1; s=mail; d=example.net; c=simple; q=dns; b=Fg…5J
Out-going message
Authentication-Results: example.net [email protected]; domainkeys=pass;
In-coming message
Send signed email
Accredited DomainKeys Accredited DomainKeys ArchitectureArchitecture
Aims at establishing trust in the sender domain Aims at establishing trust in the sender domain – Scalability, efficiency, and usabilityScalability, efficiency, and usability
Extends DomainKeys frameworkExtends DomainKeys framework– Applicable also to Identified Internet Mail (Fenton, Applicable also to Identified Internet Mail (Fenton,
Thomas)Thomas)
Introduces a trusted third-party: Introduces a trusted third-party: accreditation accreditation bureaubureau– Accreditation bureau generates and updates Accreditation bureau generates and updates
accreditation sealsaccreditation seals for registered domains for registered domains– The accreditation seal is the proof of membershipThe accreditation seal is the proof of membership– Time quantum of seal updates depends on applicationsTime quantum of seal updates depends on applications
Send in Accredited DomainKeysSend in Accredited DomainKeys
Example.net Name Server
Example.net MTA
Bob
Write mail
Private key
Public key
Register public key Accreditation Bureau
Update seal at each time quantum
Accredited-DomainKeys: v=sealDomainKey-Signature: a=rsa-sha1; s=mail; d=example.net; c=simple; q=dns; b=Fg…5J
Yahoo.com MTA
Send signed email
Sign email
Receive in Accredited DomainKeysReceive in Accredited DomainKeys
Yahoo.com MTA
Query for public keyVerify signature
Query for accreditation sealVerify seal
Accreditation Bureau
Example.net Name Server
Update accreditation seal at each time quantum
Alice from Yahoo.com
Receive mail
Authentication-Results: example.net [email protected]; domainkeys=pass; accreditation=pass
Seal realization: simple signatureSeal realization: simple signature
The seal is a signature The seal is a signature signed by the bureau on signed by the bureau on the public key of a domainthe public key of a domain
The seal is refreshed at The seal is refreshed at each time quantumeach time quantum
The seal is verified The seal is verified against the public key of against the public key of the accreditation bureauthe accreditation bureau
Example.net Name Server
Accreditation Bureau
Update accreditation seal at each time quantum
Seal realization: STMSSeal realization: STMSThe Secure Transaction Management System The Secure Transaction Management System [Goodrich, Tamassia et al.] implements an [Goodrich, Tamassia et al.] implements an authenticated dictionaryauthenticated dictionary
Source
Responder A
Responder BDS
DS
DS
t
Basis (signed)Updates
User
Query
Response
AnswerProofBasis (signed)
t
Seal realization: STMS (cont’d)Seal realization: STMS (cont’d)Example.net Name Server (STMS Responder)
Accreditation Bureau (STMS Source)
Update proof and basis at each time quantum
Yahoo.com MTA (STMS User)
Query for accreditation seal (proof-basis pair) Verify signature
of basis
Verify proof of domain
Obtain the bureau’s public-key
Receive mail
Seal Realizations: EfficiencySeal Realizations: EfficiencyOperation Simple SignatureSimple Signature STMSSTMS
Accreditation Accreditation BureauBureau
Update seals of Update seals of MM domains domains
NN signatures signatures11 signature signature
1.5 1.5 MM log log NN hashes hashes
Receiver MTAReceiver MTA
Verify seals of Verify seals of DD domains domains
DD signature verifications signature verifications11 signature verification signature verification
1.5 1.5 DD log log NN hasheshashes
Sender Name Sender Name Server Server
Provide sealProvide seal 11 signature transmitted signature transmitted1 1 signature transmittedsignature transmitted
1.5 log 1.5 log NN hashes hashes transmittedtransmitted
N: Number of domains registered with the accreditation bureau
Summary and Future WorkSummary and Future WorkSummarySummary– Accredited DK provides Accredited DK provides assurance of sender’s public key
and evidence of sender domain’s trustworthiness– Extension of DK frameworkExtension of DK framework– Accreditation seals issued by accreditation bureau and Accreditation seals issued by accreditation bureau and
stored in domain name serverstored in domain name server– STMS approach is more scalable than simple signature STMS approach is more scalable than simple signature
approachapproach
– Website:Website: http://www.accrediteddomainkeys.nethttp://www.accrediteddomainkeys.net
Current and Future Work Current and Future Work – Performance testsPerformance tests– Accredited DKIM Accredited DKIM
Related WorkRelated Work
SPF (SPF (Lentczner, Wong) and Sender ID Sender ID Framework (Microsoft)Framework (Microsoft)DomainKeys (Delany)DomainKeys (Delany)Identified Internet Mail (Fenton, Thomas)Identified Internet Mail (Fenton, Thomas)Flexible Sender Validation (Levine)Flexible Sender Validation (Levine)Sender Authorization with RMX DNS RR Sender Authorization with RMX DNS RR (Danisch)(Danisch)Reverse DNS Marking (Reverse DNS Marking (Stumpf, Hoehne))Project Lumos (Email Service Provider Coalition)Project Lumos (Email Service Provider Coalition)Authenticated data structures (Goodrich, Authenticated data structures (Goodrich, Tamassia et al.)Tamassia et al.)
AcknowledgementsAcknowledgements
David Croston and IAM Registry, IncDavid Croston and IAM Registry, Inc
David Ellis, John Nuber
Eric Allman, Jon Callas, Mark Delany, and Jim Fenton
National Science Foundation