escrypt GmbH for Embedded Security A Generic Architecture and - - PowerPoint PPT Presentation

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escrypt GmbH for Embedded Security A Generic Architecture and - - PowerPoint PPT Presentation

Sep 20, 2023 432 likes •631 views

System Provider escrypt GmbH for Embedded Security A Generic Architecture and Extension of eCryptfs: Secret Sharing Scheme, Smartcard Integration and a new Linux Security Module Daniel Bumeyer 2 , Benedikt Driessen 1 , Andr Osterhues 1 ,

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System Provider for Embedded Security

escrypt GmbH

A Generic Architecture and Extension of eCryptfs: Secret Sharing Scheme, Smartcard Integration and a new Linux Security Module

Daniel Bußmeyer2, Benedikt Driessen1, André Osterhues1, Jan Pelzl1, Volker Reiß1, Jörg Schwenk2, Christoph Wegener2

1escrypt GmbH – Embedded Security, Bochum 2Chair for Network and Data Security (NDS), Ruhr-University Bochum

escrypt GmbH Lise-Meitner-Allee 4 44801 Bochum info@escrypt.com phone: +49(0)234 43 870 209 fax: +49(0)234 43 870 211

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info@escrypt.com

29/10/2009 escrypt GmbH - Embedded Security 2

  • Introduction
  • Generic security architecture
  • Linux Security Module – esCAP
  • Integration of eCryptfs
  • Secret Sharing Scheme
  • Smartcard Integration
  • Implementation Details
  • Conclusion

Overview

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  • Goal: handle security-sensitive data in Linux environments
  • Encryption systems:
  • File encryption systems:
  • GnuPG
  • Device/partition encryption systems:
  • DM-Crypt, TrueCrypt, eCryptfs
  • Security often depends on strength of chosen password

Introduction

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29/10/2009 escrypt GmbH - Embedded Security 4

  • Weak passwords -> vulnerable to dictionary and/or social

engineering attacks

  • Single key for single user -> single point of failure
  • User can (accidentally) write data to insecure places (USB

sticks, email)

  • System admin (superuser) can access keys (using exploits,

tracing/debugging processes etc.)

Introduction – Problems

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  • Weak passwords: use smartcards instead
  • Single key for single user: secret sharing scheme
  • User can (accidentally) write data to insecure places (USB

sticks, email): restrict user by applying access control using a Linux Security Module

  • System admin (superuser) can access keys: restrict root

user by applying access control using a Linux Security Module

Introduction – Solution concepts

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Generic Security Architecture

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  • Security-critical data is stored in encrypted form on a central

server

  • Limit superuser:
  • Still can administer most services and infrastructure (e.g., backups)
  • No access to security-critical data, keys or configuration files
  • Mandatory Access Control (MAC) mechanism called “esCAP”
  • Device encryption (eCryptfs) using symmetric keys
  • FEK: File encryption key, per file
  • FEKEK: FEK encryption key, per device/partition
  • Asymmetric cryptography (RSA)
  • Encrypt symmetric keys (FEKEKs)
  • Based on smartcards, RSA private key never leaves smartcard

Generic Security Architecture

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29/10/2009 escrypt GmbH - Embedded Security 8

  • Mandatory Access Control system, in-kernel
  • Subjects:

tasks or processes

  • Objects:

tasks, keys or inodes

  • Association:

read/write access

  • Rule: Subject S may or may not read/write an object O
  • Rules are set using esCAP’s procfs interface
  • Fast interpretation of rules, virtually no performance penalty

Linux Security Module – esCAP

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29/10/2009 escrypt GmbH - Embedded Security 9

  • Object-specific rules
  • Defined at run-time by giving subject, object and association
  • Control read/write access, signals, debugging
  • Limit access (read/write/search) to kernel keyrings
  • Special case: File “firewall”
  • Notification on file access
  • Applet forwards notification to user
  • Generation of dynamic rule depending on user decision
  • Global rules
  • Defined at startup
  • Enable/disable module loading
  • Enable/disable raw sockets

Linux Security Module – esCAP

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29/10/2009 escrypt GmbH - Embedded Security 10

  • Wrapper library
  • Attach symmetric key to user’s keyring
  • Remove a key from user’s keyring
  • Mount a directory
  • Unmount a directory
  • PKI module for eCryptfs
  • AES Key Wrap algorithm [NIST 2001]
  • Encrypt/decrypt symmetric file keys (FEKs) using a symmetric

directory key (FEKEK)

  • FEKEK is encrypted with the smartcard’s public key (RSA-2048)
  • FEKEK can only be decrypted using the private key, which remains
  • n the smartcard

Integration of eCryptfs

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29/10/2009 escrypt GmbH - Embedded Security 11

  • Idea: distribute a secret (key) among a group of n users
  • Secret is split into n parts
  • Threshold k with 2 ≤ k ≤ n: amount of users required to

reconstruct the secret

  • Used for emergency file access in our system:
  • For each new directory, a secret sharing group and threshold k is

defined

  • The directory’s FEKEK is split among the secret sharing users
  • In an emergency case, k of the users can reconstruct the secret and

access the directory

Secret Sharing Scheme

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29/10/2009 escrypt GmbH - Embedded Security 12

  • Generic smartcard interface:
  • Decryption
  • Signature generation
  • Read bytes from random number generator (RNG)
  • Read/write files
  • Smartcard requirements:
  • Asymmetric cryptography (RSA decryption and signing)
  • Secure storage (for private key)
  • Minimal filesystem (for the public key and certificates)
  • True random number generator (TRNG)
  • Supported smartcards:
  • eDA (elektronischer Dienstausweis, “electronic office ID card”)

Smartcard Integration

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Implementation Details – Overview

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  • Control:

Central module, message passing

  • GUI:

Graphical User Interface

  • DirCache:

Cache of directory-related information from DirHeader

  • Smartcard:

Smartcard interface

  • esCAP Applet:

GUI for “file firewall” function of esCAP

Implementation Details – Client-side Modules

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  • Daemon:

Central module, XML script interpretation and message passing

  • CertStore:

User certificate storage

  • DirHeader:

Information about each directory

  • DataBase:

List of user’s directories

  • Secret Sharing:

Secret sharing implementation

  • FireWall:

Netfilter configuration, dynamic rules

  • esCAP:

Interface to esCAP kernel module

  • FileSystem:

Interface to eCryptfs

Implementation Details – Server-side Modules

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  • Programming language:
  • C++ for framework and modules
  • C for esCAP and eCryptfs PKI module
  • Message flow:
  • Definition of use cases
  • UML 2.0 sequence diagrams
  • XML scripts
  • Small and simple XML parser
  • Command interpreter in Daemon
  • Easy adoption of use cases by changing the XML script
  • Hardware:
  • Standard smartcard readers

Implementation Details

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  • Software suite:
  • User-friendly GUI
  • Command-line tools for security administrator and system

administrator

  • Based on a Fedora 10 distribution
  • Slightly modified Linux 2.6.26 kernel (patches include esCAP and

eCryptfs modifications)

  • Demonstrator already available, prototype in near future
  • Project homepage: http://sourceforge.net/projects/esosi
  • License: LGPL

Conclusion

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Dr.-Ing. Jan Pelzl Geschäftsführer jpelzl@escrypt.com Dr.-Ing. Thomas Wollinger Geschäftsführer twollinger@escrypt.com Dr.-Ing. André Weimerskirch CEO USA aweimerskirch@escrypt.com

escrypt GmbH Lise-Meitner-Allee 4 44801 Bochum info@escrypt.com phone: +49(0)234 43 870 209 fax: +49(0)234 43 870 211