1 / 15

Authentication in Dist Systems

Authentication in Dist Systems. Presented in cs294-4 P2P Systems by Sailesh Krishnamurthy Oct 1 2003. Access Control Authentication. Model elements: Objects, resources (files,processes etc) Requests to perform operations on objects Principals - request sources, use Channels

rtorres
Download Presentation

Authentication in Dist Systems

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Authentication in Dist Systems Presented in cs294-4 P2P Systems by Sailesh Krishnamurthy Oct 1 2003

  2. Access Control Authentication • Model elements: • Objects, resources (files,processes etc) • Requests to perform operations on objects • Principals - request sources, use Channels • Guardian - request validator • Easy in centralized systems • OS implements all channels, “knows” all principals • Hard in distributed systems • Long path from request originator • Different kinds of channels • Parts can break, get inaccessible

  3. Paper contributions • Authentication theory for distributed systems (why theory ?) • Assumptions about authority and trust • Formally represent these assumptions • Carefully examine the assumptions • Describes a practical system based on the theory • Uses the theory to explain several mechanisms

  4. Concepts • Principals • Simple • People: Lampson, Abadi • Machines: coeus, mammoth • Roles: manager, secretary • Named sets of principals: Services, Groups • Channels (principals that “say” things) • Wires, IO ports, N/W addr, encryption keys • Compound principals • Roles: Abadi as manager • Delegations: Mike for Burrows • Conjunctions: Lampson ^ Wobber

  5. Statements • Statements - made by principals • Simple: request for file foobar.tex • Compound: Bob as secretary requests file bar.tex • Trusted Computing Base - keep it small

  6. Statements • Primitive statements (e.g. “read file foo”) • s^s’ (s and s’) • s  s’ (s implies s’) • s  s’ (s is equivalent to s’) • If ‘A’ is a principal and ‘s’ is a statement, • A says s is a statement • If ‘A’ and ‘B’ are principals • AB (A speaks for B) is a statement • A | B ( A quotes B) is a statement

  7. More on statements • Needham-Schroeder auth ticket • {Kab,A}Ks can be written:Kbs says Kab  A • If ‘s’ is an axiom it is represented as s. • Some axioms: • (A says s ^ A says (s  s’))  A says s’ • If s then A says s for every principal A • A says (s ^ s’)  (A says s) ^ (A says s’)

  8. Principals • Let ‘A’ and ‘B’ be principals, ‘C’ be a channel. • (A^B) says s  (A says s) ^ (B says s) • (A|B) says s  (A says B says s) • What if A lied - B did not say s ? • (AB)  ((A says s)  (B says s))

  9. Tools: handoffs, joint authorities • (A says (B  A))  (B  A) • If you see A says s, simply conclude ‘s’ if it is of the form B  A. • Simply states that A allows B to speak for itself. • Third Parties! • ((A’  A) ^ A’ says (BA))  (B  A) • Joint Authorities • ((A’^B  B) ^ (B  A’))  (B  A)

  10. Joint authorities • Useful for certificate revocation • Refreshing requires source availability • Hard to make a source that is both: • Secure • Highly available • Solution: use 2 sources • One is highly secure with a long lifetime • Other is highly available, uses a short lifetime • However, both must agree to validate certificate

  11. Channels and Encryption • Encryption channel: • Dec(K,Enc(K-1,x)) = x for a message x • Encryption enforces: • Security: If you know Enc(K-1,x) but not K, then should not be able to compute x • Integrity: If you know x but not K-1 should not compute a y such that Dec(K,y) = x • 2 forms: public keys, shared keys • Public keys can be simulated with stateless symmetric key

  12. Named principals • Pull vs Push to get credentials • Pull: receiver looks up named principal to get credential • Push: sender provides credentials • CA: external certificate authority • Paths: able to trace “up” and “down” an authority tree • Groups:Members “speak for” groups • Certificates: P1 => G, P2 => G etc. • Or, for each member Pi, store Enc(Kp,Kg-1) in G’s database

  13. Roles and Programs • Can be run with different priorities • Use digests (MD5) of prog text to confirm identity • Similar to booting a machine • Different OS’s on a given machine

  14. Other stuff • Delegation • Login (session keys) • Authenticating IPC • Use authenticating agents • Access Control • Standard ACL plus theory

  15. Relevance to P2P systems ? • How can peers authenticate themselves to each other ? • RIAA trace lookups for file sharing systems ? • Authenticate steps in multiple-hop DHTs (like Chord/Viceroy) in a manner similar to the paths ?

More Related