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Security Protocols in Automation

Security Protocols in Automation. Dwaine Clarke declarke@mit.edu MIT Laboratory for Computer Science January 8, 2002. With help from: Matt Burnside, Todd Mills, Andrew Maywah, Srinivas Devadas, Ronald Rivest. Overview. Problem Description SPKI/SDSI Introduction Name Certificate

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Security Protocols in Automation

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  1. Security Protocols in Automation Dwaine Clarke declarke@mit.edu MIT Laboratory for Computer Science January 8, 2002 With help from: Matt Burnside, Todd Mills, Andrew Maywah, Srinivas Devadas, Ronald Rivest

  2. Overview • Problem Description • SPKI/SDSI Introduction • Name Certificate • Authorization Certificate • Proxy-to-Proxy protocol • Examples • Status • Questions

  3. Name Resolution Routing SPKI/SDSI Over SSL/TLS SPKI/SDSI Over SSL/TLS K21 K21 Proxy VCR Proxy Scripting Problem: Proxy to Proxy Security All proxies talk to each other with the same protocol

  4. SPKI/SDSI Introduction(Simple Public-Key Infrastructure/Simple Distributed Security Infrastructure) • Build secure distributed computing systems • Access control over the network • Simple, flexible, trust policy model with specific authorizations • Fine-grained access control • Scalable infrastructure

  5. SPKI/SDSI Introduction(Simple Public-Key Infrastructure/Simple Distributed Security Infrastructure) • Designed by Ron Rivest, Butler Lampson and Carl Ellison • Each public key is a CA • Name certificate: defines a name in issuer’s name space • Authorization certificate: grants a specific authorization from issuer to subject

  6. SPKI/SDSI: {Kc friends, Kd}K {Kc friends, Ke}K {Kc friends, Kf}K Traditional: {MIT Dave_Brown, KDB}K c MIT c c If ‘Kc friends’ is on an ACL, Kd, Ke and Kf are allowed to access the object. SPKI/SDSI: Name Certificates • Local name spaces • Groups

  7. SPKI/SDSI: Name Certificate (cert (issuer (name (public-key (rsa-pkcs1-md5 (e #23#) (n |AMMgMuKpqK13pHMhC8kuxaSeCo+yt8TadcgnG8bEo+erdrSBveY3C MBkkZqrM0St4KkmMuHMXhsp5FX71XBiVW1+JGCBLfI7hxWDZCxGTMg bR4Fk+ctyUxIv3CQ93uYVkg9ca6awCxtS0EI7sLuEB+HKuOLjzTsH+ +Txw9NAHq4r|))) friends)) (subject (public-key (rsa-pkcs1-md5 (e #23#) (n |AKg3tOzoJ5PGQ5q9jzxzwxE8o6bIZ6/cE8gEL+1xJa23viE3bz68ru hpD5muqJ+uyDCNxgAZ0JVXJazmX1QjiGudj9kEmuni8gJRLZRu0T5E3 K7OU2dodu0kdDg32kym7+ooZNe/F0zWGekfESeezyQ25kvNO3XQvMHX afWcYjRw|)))))

  8. SPKI/SDSI: Authorization Model • Simple trust policy model • Authorizations specified in flexible, user-defined tags • Authorizations can be defined as specific or as general as the user desires • Delegation (specific)

  9. SPKI/SDSI: Authorization Certificate (cert (issuer (public-key (rsa-pkcs1-md5 (e #23#) (n |AMMgMuKpqK13pHMhC8kuxaSeCo+yt8TadcgnG8bEo+erdrSBveY3C MBkkZqrM0St4KkmMuHMXhsp5FX71XBiVW1+JGCBLfI7hxWDZCxGTMg bR4Fk+ctyUxIv3CQ93uYVkg9ca6awCxtS0EI7sLuEB+HKuOLjzTsH+ +Txw9NAHq4r|)))) (subject (public-key (rsa-pkcs1-md5 (e #23#) (n |AKg3tOzoJ5PGQ5q9jzxzwxE8o6bIZ6/cE8gEL+1xJa23viE3bz68ru hpD5muqJ+uyDCNxgAZ0JVXJazmX1QjiGudj9kEmuni8gJRLZRu0T5E3 K7OU2dodu0kdDg32kym7+ooZNe/F0zWGekfESeezyQ25kvNO3XQvMHX afWcYjRw|)))) (tag (http (* set GET POST) (* prefix http://ostrich.lcs.mit.edu/demo/))) (propagate))

  10. SPKI/SDSI: Tag (tag (http (* set GET POST) (* prefix http://ostrich.lcs.mit.edu/demo/))) Intuitively, a tag is a set of requests.

  11. Proxy to Proxy Initialization: Alice (Client Proxy) Bob (Server Proxy) Da (private key) Ea (public key) Alice’s client certs List of CA certs Db (private key) Eb (public key) ACL Server certs • Set up SSL connection: • Server auth • Session key for privacy • Freshness • Protection from MIM

  12. Proxy to ProxyCase 1: user’s key is directly on the ACL Alice (Client) Bob (Server) [tag]Da Db (private key) Eb (public key) ACL Server certs Da (private key) Ea (public key) Alice’s client certs List of CA certs Response ACL: {Ec, Eb, Ea}

  13. Alice (Client Proxy) Bob (Server Proxy) [tag]Da Db (private key) Eb (public key) ACL Server certs Da (private key) Ea (public key) Alice’s client certs List of CA certs Rejected: ACL [tag]Da, certs Proxy to Proxy Case 2: user’s key is “indirectly” on the ACL ACL: {‘Eb friends’} Client performs certificate chain discovery. Server verifies certificate chain.

  14. Certificate Chaining Example • Bob’s ACL says only MIT faculty are allowed to access his server. • Alice’s first request is simply signed with Alice’s key, and Bob rejects this request. • Alice’s second request contains a chain consisting of the following certificates: • A certificate saying she is anLCS Professor • A second certificate sayingLCS ProfessorsareMIT faculty

  15. Certificate Chain Discovery(Client Proxy) • Derive certificate chains • Input: device’s ACL, requestor’s public key, requestor’s set of signed certificates, tag • Output: a chain of certificates leading from an entry on the ACL to the requestor’s public key. • (The certificate chain consists of signed certificates. It proves that the requestor is authorized to perform the tag’s operations on the device.) * Recall, intuitively, a tag is a set of requests.

  16. Certificate Chain Verification (Server Proxy) • Verify certificate chains • Input: device’s ACL, requestor’s public key, requestor’s certificate chain, tag • Output: 1 if certificate chain proves that the public key is authorized to perform the tag’s operations on the device; 0 otherwise.

  17. Proxy to Proxy Case 2 revisited user’s key is “indirectly” on the ACL Alice (Client Proxy) Bob (Server Proxy) [tag]Da Db (private key) Eb (public key) ACL Server certs Da (private key) Ea (public key) Alice’s client certs List of CA certs Rejected: ACL [tag]Da, certs • Signed request provides proof of authenticity of the request • Certificate chain provides proof that the request is authorized

  18. [tag]Dm “ok” 1. Mary sends request (either signed or unsigned) via her proxy to the light switch’s proxy. 2. Light switch’s proxy has no ACL. It honors Mary’s request. Example: Public resource Mary wants to turn on/off a public light switch. Light switch’s proxy may require requests to be signed for auditing purposes.

  19. [tag]Dm “ok” • Mary sends signed request via her proxy to the dialup’s proxy. 2. Dialup’s proxy has an ACL which contains Mary’s public-key. It checks the signature on Mary’s request, and honors Mary’s request to login if the signature verifies. Example: user’s key directly on ACL Mary wants to log into an account on a dialup machine. ACL: {Ec, Ef, Em}

  20. [tag]Dm [tag]Dm, cert chain “ok” ACL • Mary sends signed request via her proxy to John’s speaker’s proxy. 2. John’s speaker’s proxy rejects first request, and returns the ACL. 3. Mary’s proxy uses the Cert Chain Discovery Algorithm to derive a chain of certificates proving that Mary is a member of the groupJohn’s friends. Mary sends the certificate chain and signed request to John’s speaker’s proxy. 4. John’s speaker’s proxy verifies second request. Mary wants to play music on John’s speaker. Example:user’s key is indirectly on ACL ACL: {‘Ej friends’}

  21. Summary:Issues we are dealing with • Specifying, granting, delegating and revoking authorizations • Creating, maintaining and auditing groups • Attribute searching • Facilitating scalability • Designing simple, user-friendly systems

  22. Questions?

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