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Security Service
 Why do we need security in distributed system?
 Examples: banking, e-commerce, personal info, classified info
 Distributed systems are inherently insecure
 network
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 Security Requirements
 Confidentiality
 Integrity
 Accountability
 Availability
 threats to Security
 Gaining access directly
 Obtaining authorized user info and access
 Obtaining info through monitoring the comm. Channel
 Modifying messages on the comm. Channel
 Performing untraceable malicious actions
 Denying participations
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 Categories of threats
 Leakage: unauthorized disclosure of information
 Tempering: unauthorized modification of information
 Resource stealing: unauthorized use of computing resources
 Vandalism: destruction of information
 Combined threats
 Methods of Attack
 Masquerading: obtain the identity of legitimate users
 Eavesdropping: listen to and decode request message
 Tampering : modify request messages
 Replaying: repetition of request messages
 Infiltration:
 Attacks by legitimate users
 Obtaining a legitimate user’s identity
 Smuggling client or server objects, virus,worms
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 Security Service Features
 Identification and authentication
 Authorization and access control
 Auditing
 Communications security
 Non-repudiation
 Administration of security policy
 Encryption
 Encryption uses an algorithm and a key to convert plain text into cypher text
and vice versa
 Secrete key
 Public key
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Secrete Key Encryption
 Secrete keys are known to two parties and not disclosed to any others
 Use the same key for both encrypting and decrypting messages
 Encryption and decryption functions may be public
 The encryption and decryption are performed after the stubs have completed
request marshalling and unmarshalling and it has been recognized that the
server object is not local
 Encryption can be kept entirely transparent for client and server programmer
 Encryption is done by middleware or by stubs that are created by middleware
 Distribution of secrete keys to large numbers of objects is too complex
Client A
1.
2.
3.
Server B
Caller
Called
Stub
Stub
Acquire Kab
f(Kab, M)  {M}kab
send
{M}kab
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1.
2.
3.
Acquire Kab
Receive
f’(Kab, {M}kab)  M
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Public Key Encryption
 Public key encryption generate pairs of keys of which one is made publicly
available and the other is kept private
 Number of keys is only linear in relation to the number of objects
 The execution of encryption and decryption function is more complex
Client A
1.
2.
3.
Server B
Caller
Called
Stub
Stub
Acquire Kab
f(Kpb, M)  {M}kpb
send
{M}kpb
Security Service
1.
2.
3.
4.
Generate (Kpb, Ksb)
Publish Kpb
Receive
g(Ksb, {M}kpb)  M
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Key Distribution
 Secure key distribution mechanisms are needed for both secret
and public key encryption
 Key distribution service
 Service has to be a trusted service
 The registration of object with that service has to be trustworthy
 Needham/Schroeder protocol
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Key Distribution
 Distributing secrete keys
1:C,S,NC
Key Distribution
Server AS
2:{NC, S, KCS, {KCS, C}KS}KC
3:{KCS, C}KS
Client
C
4:{NS}Kcs
Server
S
5:{NS-1}Kcs
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Key Distribution
 Distributing public keys
1:C,S
Key Distribution
Server AS
4:S, C
5:{KPC, A}KSAS
2:{KPS, S}KSAS
3:{NC, C}KPS
Client
C
Server
S
6:{NC, NS}KPC
7:{NS}KPS
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Higher-Level Security Services
 Security Service Features
 Firewalls
 Identification and authentication
 Authorization and access control
 Auditing
 Non-repudiation
 Communications security
 Administration of security policy
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Firewalls
 Firewalls are gateways that tightly control message traffic
between private and public networks
 Levels of control can vary
 Monitor and audit network traffic
 Allow/disallow certain types of packet through
 Does not impact a distributed object systems if comm. does not pass through
firewall (both in private network, or both in public network, etc).
 Distributed object firewalls that understand the message traffic exchanged
between clients and servers
 Firewalls between distributed objects have to understand the encoding of object
request
 Firewalls have to be integrated with encryption techniques
Private
Network
Firewall
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Public
Network
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Firewalls
outbound firewalls
FWC1
FWC2
inbound firewalls
FWS1
FWS2
Client
Server
enclave C1
enclave S2
enclave C2
enclave S1
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Types of Firewalls
 Packet Filtering
 Allow all kinds of packets, but only to this IP address and this port
 Allow incoming traffic only from the specified IP subnets
 Application-level gateways (Figure 12.4)
 CORBA and Firewalls
 HTTP Tunneling: an IIOP request is enclosed in an HTTP envelope and sent
via the HTTP protocol (Figure 12.5)
 GIOP Proxies: callbacks
 Security Socket Layer
 A protocol on top of TCP/IP that adds security capabilities
 SSL API is an extension to the TCP/IP socket API
 Encryption of messages
 Authentication of the server based on digital certificates and signatures
 Optional authentication of the cleint
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Authentication
 Authentication techniques establish trust in a principal and its
credentials
 Both client and server objects are necessary to be authenticated
 Authentication is implemented using encryption
 Challenge-response protocol
:AuthenticationServer
:Client
authenticate()
challenge
response()
credentials
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Credentials
Credentials
authenticated attributes
Unauthenticated
attributes
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Identity
attributes
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Access Control
 Access control mechanisms decide whether or not an object
request can be granted to a client object
 A principal is a human user or a system entity that is registered in and
authenticated to a system
 Credentials contain the security attributes of a principal
 Object invocation access policies determine whether a particular principal is
allowed to perform an object request
 Two forms of access policies:
 Object invocation access policies are implemented by the object-oriented
middleware
 Application object access policies are enforced at an application level and
implemented by the application developer
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Perspective on Access Control
 Client’s perspective
 A request is either granted or not
 Server’s perspective
 Object invocation access policy is used: access control is transparent to the
server programmer --- implemented by middleware
 Application object access policy is used: server programmer must implement
the access decision function. Input to the function is:
 Credentials of the principal that requested an operation execution
 Reference of the server object from which an execution is requested
 Request operation
 Parameters of the requested operation
 Admin’s Perspective
 Object invocation access policy is not transparent to admin.
 Access rights define the modes of access that principals have to server objects
 Access rights are often defined for types rather than objects
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 Privileges and Privilege Delegation Scheme
 Own privilege
 Caller’s privilege
 Combined privilege
 Use both
 Combine and generate new credentials
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Security Model
Credentials
Current
Target
Object
Client
Credentials
Current
Binding
ORB Security
ORB Security
Access Control
Access Control
Secure Invocation
Secure Invocation
ORB CORE
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Security Service
 Security Model
 Clients, target objects, operation invocations
 Building request  transmitting the request  executing an operation 
sending a reply
 Figure 12.8 Security Service is closely tied with ORB and is not an
independent object service, but an ORB service
 Security-aware applications vs Security-unaware applications
 Principles and Security Attributes (Figure 12.9)
 Establish a security association:
 usually, client trust, server authenticate
 Binding between client and target
 Security service provide current execution context (current)
 Target object or Security Service decides operation permissions based on the
current. (Access control …)
 Auditing through auditing channel if required.
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Security Conformance Levels
 Security Conformance Levels
 Level allows ORB security to be applied to applications that are not securityaware: authentication; security policies; provision of message integrity and
confidentiality; access control policy
 Level 2 = level 1 + enhanced integrity + trust + auditing
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Security Service
 Higher-Level Security Services
 Firewalls: gateways that tightly control message traffic between private and
public network
 Authentication: establish trust in a principal and its credentials
 Access control: decide whether or not an object request can be granted to a
client object
 Client: request is either granted or not
 Server:
– Performed by middleware (invocation policy define on object)
– Server application make access control decisions based on the data:
Request credentials
References to server objects
Requested operations
Parameters to the requested operations
 Admin:
– Define the modes of access that principals have to server objects
– Access rights are defined for types rather than objects
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Security Service
 Non-repudiation Services
 Evidence Generation and Verification
 Evidence Storage and Retrieval
 Delivery Authority
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Non-repudiation Services
Object A
Object B
Dispute/
Judgement
Service Req./Rep.
Nonrepudiation Services
Evidence Generation and Verification
Adjudicator
Service
Req./Rep.
Evidence Storage and Retrieval
Delivery Authority
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Security Service
 Security Domains
 Security Policies:
 Hierarchy
 Overlap
 Conflict
 Finding the Security Features of an ORB
Get_service_information()
 Authentication of a User Principal
 Selecting Privileges
Credentials: get_credentials(); set_privileges()
 Making a Security Invocation
Access_Decision object, access_allowed();
AuditDecision object, audit_needed(); audit_channel()
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Security Service
 Non-repudiation
 Generate_token(): generate an unforgeable token to be used in the evidence
 Verify_evidence(): check if evidence is valid
 Form_complete_evidence(): use original token to generate further evidence,
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Security Service
 Application Security Interfaces
 Common Security Types
 Security Level 1 (for security-unaware applications)
Interface Current:CORBA:Current{//PIDL
Security::AttributeList get_attributes(in Security::AttributeTypeList attributes);
};
For level 1, only allow the client to know what attributes are available
 Security Level 2 (for security-aware applications)
Current interface inherits the one form SecurityLevel1, extends functionality with
references to the following objects: RequiredRights, AccessDecision,
AuditDecision, and PrincipalAuthenticator, and Credentials objects.
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Security Service
 RequiredRights
 Get_required_rights()
 Set_required_rights()
 PrincipalAuthenticator
 Get_supported_authen_methods();
 Authenticate();
 Continue_authentication();
 Credentials
 Copy()
 Destroy()
 Get_security_feature()
 Get_attributes()
 Set_privileges();
 Is_valid();
 Refresh();
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Security Service
 Object
 Get_policy()
 Get_domain_managers()
 Set_policy_overrides()
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