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Computer Security. Tran, Van Hoai Department of Systems & Networking Faculty of Computer Science & Engineering HCMC University of Technology. Outline. Introduction to security Secure channels Access control Security management Example: electronic payment systems.
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Computer Security Tran, Van Hoai Department of Systems & Networking Faculty of Computer Science & Engineering HCMC University of Technology
Outline • Introduction to security • Secure channels • Access control • Security management • Example: electronic payment systems 2009-2010
Security concerns in distributed systems SECURE CHANNELS authentication message integrity confidentiality ACCESS CONTROL authorization
What are security threats ? (1) • Interception: an unauthorized party has gained access to resource • communication between 2 parties has been overheard by someone else • data illegally copied after breaking into private directoty • Interrupt: resources unavailable, unusable, destroyed,… • Denial of Service
What are security threats ? (2) • Modification: unauthorizedchanging of data or tampering with a service so that it loses original specifications • changing program to log secretly user’s activities • Fabrication: additional data or activity generated that would normally not exist • add an entry to password file
Security policy & security mechanisms • Building a secure system is not to protect against all threats • First, security policies must be created Security policy= to describe which actions the entities are allowed to take and which ones are prohibited Security mechanism = to enforce security policies
Security mechanisms • Encryption • hacker cannot understand (cryptography) • provide confidentiality, integrity • Authentication • verify a claimed identity • Authorization • check permissions (rights) to perform actions • Auditing • trace clients’ access
Design issuesFocus of control – protection on data Data is protected against wrong or invalid operations State Object Operations can be performed, but main concern is data integrity Method Invocation
Design issuesFocus of control – protection on invocation Data is protected against unauthorized invocations State Object Main concern is access control mechanisms Method Invocation
Design issuesFocus of control – protection on user Data is protected by checking the role of invoker State Object Main concern is defining roles that users have Method Invocation
Design issuesLayer of security mechanisms Application Application Main concern is where security mechanisms are placed high-level protocols Middleware Middleware OS Services OS Services Transport Transport IDEA: TRUST depending on the trust a client has in how secure the services are in a particular layer OS kernel OS kernel low-level protocols Network Network Datalink Datalink Hardware Hardware Physical Physical network
Trust on different layers SMDS In distributed system, security mechanisms often placed in middleware Encryption device Different LANs trust each other, but do not trust SMDS Trust router(encryption device) If not Use SSL
Design issuesDistribution of security mechanisms • Middleware-base distributed system trusts local OS it depends on • If not, part of functionality of OS must be integrated in distributed system • Use the approach “Reduced Interfaces for Secure System Components” no direct access from other machines servers running secure services access control device
Design issuesSimplicity • Few, simple security mechanisms easily understood and trusted to work, the better it is • It is not easy in practice • Applications are inherently complex, therefore security services, protocols should be simple
Cryptography Active intruderscan alter messages Active intruderscan insert messages Passive intrudersonly listen to C Symmetric cryptosystems: DES Public-key cryptosystems: RSA Hash functions: MD5 Encryption method Decryption method CiphertextC=EK(P) Plaintext, P Plaintext, P Encryption key, EK Decryption key, DK Sender Receiver
Secure channels • Protecting clients and servers against • interception: ensureing confidentiality • modification, fabrication: mutual authentication and message integrity • authentication and message integrity must go together • Ex: A sends B a message m. A and B both authenticated, but how guaranteeing m is not modified
Authentication based on shared secret key • Challenge-response protocol • RA, RB: challenge from A, B respectively • KA,B: secret key shared by A, B ALICE 1 BOB A 2 RB - Key distribution center can reduce number of keys - No longer used because defeated by reflection attack 3 KA,B(RB) 4 RA 5 KA,B(RA)
Authentication based on public-key cryptography • KA+, KA-: public and private keys of A respectively • KA,B: session key shared by A, B ALICE 1 BOB KB+(A, RA) 2 KA+(RA,RB,KA,B) 3 KA,B(RB)
Digital signatures • Example: • Bob sells Alice an item with price $500 • Alice sends Bob an email to confirm • Two issues happen • Alice needs to be sured Bob maliciously change to price to higher value • Bob needs to be sures Alice cannot deny the price (preventing second thoughts) Require a signature associated with the email’s content
Digital signature using public-key Alice’s computer Bob’s computer Alice’s publickey, KA+ Alice’s private key, KA- Bob’s public key, KB+ Bob’s privatekey, KB- m m KA-(m) KA-(m) KB+(m, KA-(m))
