Separating Key Management from File System Security

1
Separating Key Management from File System
Security

• Presented by M. S. Ali
• Instructor Prof. Stefan Sariou
• CSC 2231
• Online Social Networking Systems
• November 29, 2007

2
Outline

• Introduction
• Internet-scale File Distribution
• How it Works
• Self-Certifying Pathnames
• Authentication PKI / SPR
• Other Approaches
• Discussion
• Conclusion

3
Introduction

• Self-certifying File System (SFS)
• Secure, non-centralized, simple access
• Portable across administration realms
• Independent of key management
• Use encryption over wire
• Replace system-specific identifiers with secure
  tokens (SPR, file handles)
• Implemented on NFS

4
Internet-scale File Distribution

• Access files from any client
• Consistent file names across all clients
• Simplify access to file stores
• Localize administration
• Simplify authentication across realms
• Trust servers and clients
• Assume hostile network in between

5
How it Works
sfsclient client terminals
sfscd client daemon
CLIENT
server mappings
nfsmount
R
RW
sfsagents file protocols
nfsmount
R
RW
sfssd server daemon
FILE SERVER
NFS
Modular set of client/server tools to access
files in NFS using SUN RPC
6
Self-Certifying Pathnames

• Public certificate key
• Location of server (DNS/IP)
• Root directory is always /sfs
• Use symbolic links to chain file servers

/sfs/LOCATIONHOSTID/
LOCATION IP address or DNS of file server
HOSTID SHA-1(HostInfo, Location, PublicKey)
e.g., /sfs/sfs.mit.edubzcc5hder7cuc86kf6qswyx6yu
emnw69
7
Authentication PKI
sfsclient client terminals
sfscd client daemon
CLIENT
server mappings
sfsagent
sfsagent
authserv authenticate
FILE SERVER
Local Database
PUBLIC CERTS
Remote Database
Private certificate is stored in memory in
sfsagent
8
Authentication SPR
sfsclient client terminals
OWNER SERVER
sfscd client daemon
sfsagent
server mappings
CLIENT
authserv authenticate
sfskey
Owner Database
sfsagent
sfsagent
authserv authenticate
FILE SERVER
Local Database
Generate certificate-based authentication from
weak passwords using SPR
9
Other Approaches

• AFS Kerberos/Passwords
• Echo Single root, hierarchical
  authentication, centralized
• Truffles (w/ PEM), WebFS (HTTP)
• Others not considered
• Capability Security
• PolicyMaker

10
Discussion

• NFS bugs are the biggest security threat
• SUN ONE Ubiquitous Desktops
• Security key management file system?
• Why do we need a global-scale file system?
• Does OSN give us a clue for how to share files
  better?
• Middleman attacks ?

11
Conclusions 20/20 Vision

• Modern advances in storage and P2P
• Do very little but do it very well.
• Global key management is infeasible
• If you use certificates then you can't avoid key
  management
• Cryptography gives good end-point security
• Origination of files not considered