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Key Management

Key Management. 1. K B + (A, R A ). K A + (R A , R B ,K A,B ). 2. K A,B (R B ). 3. Authentication Using Public-Key Cryptography. K A + , K B + : public keys. Bob. Alice. What if K B + is faked?. Security Management. Problem: how do you get keys in the first place?

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Key Management

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  1. Key Management

  2. 1 KB+(A, RA) KA+(RA, RB,KA,B) 2 KA,B(RB) 3 Authentication Using Public-Key Cryptography • KA+, KB+: public keys Bob Alice • What if KB+ is faked?

  3. Security Management • Problem: how do you get keys in the first place? • Key distribution: securely associate an entity with a key • Example: Public Key Infrastructure (PKI), a system that manages public key distribution on a wide-scale • Key establishment: establish session keys • Use public key cryptography (we already know how to do it)

  4. Components of a PKI

  5. Digital Certificate • Signed data structure that binds an entity (E) with its corresponding public key (KE+) • Signed by a recognized and trusted authority, i.e., Certification Authority (CA) • Provide assurance that a particular public key belongs to a specific entity • How? • CA generates KCA-(E, KE+) • Everyone can verify signature using KCA+

  6. Certification Authority (CA) • People, processes responsible for creation, delivery and management of digital certificates • Organized in a hierarchy (use delegation – see next) Root CA CA-1 CA-2

  7. Registration Authority • People, processes and/or tools that are responsible for • Authenticating the identity of new entities (users or computing devices) • Requiring certificates from CA’s.

  8. Certificate Repository • A database which is accessible to all users of a PKI, contains: • Digital certificates, • Certificate revocation information • Policy information

  9. private key public key Alice Alice private key public key Bob Bob Example • Alice generates her own key pair. • Bob generates his own key pair. • Both sent their public key to a CA and receive a digital certificate

  10. public key Bob private key Alice public key Alice private key Bob Example • Alice gets Bob’s public key from the CA • Bob gets Alice’s public key from the CA

  11. Certificate Revocation • Process of publicly announcing that a certificate has been revoked and should no longer be used. • Approaches: • Use certificates that automatically time out • Use certificate revocation list

  12. Authorization Management

  13. Authorization Management • Granting authorization rights • Related with access control which verifies access rights

  14. Capabilities (1) • How to grant a capability? • How to verify a capability?

  15. Capabilities (2) • Capability: • Unforgeable data structure for a specific resource R • Specify access right the holder has with respect to R • An example:

  16. Capabilities (3) • Generation of a restricted capability from an owner capability Owner

  17. Delegation: Motivation Example • A user Alice has read-only access rights on a large file F • Alice wants to print F on printer P no earlier than 2am • Method A: Alice sends the entire file F to the printer P; • Method B: Alice passes the file name to P and printer P copies the file F to its spooling directory when F is actually needed. • For method B, Alice needs to delegate her read-only access rights on F to printer P

  18. Delegation: Neuman Scheme • The general structure of a proxy as used for delegation:

  19. Delegation: Neuman Scheme • Using a proxy to delegate and prove ownership of access rights • In practice S+proxy, S-proxy can be a public-private key pair and N can be a nonce

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