1
SNMPv3
by
Behzad Akbari
Fall 2011
In the Name of the Most High
These slides are based in parts upon slides of Prof. Dssouli (Concordia university)
2
Key Features of SNMPv3
Modularization of documentation and architecture Enables the use of SNMPv1 and SNMPv2 with the newly
developed SNMPv3.
SNMP engine defined – A model for the processing of SNMP messages.
New Security features – Secure information to prevent tampering of data – Access control to determine proper access to MIB.
3
Documentation
SNMP Architecture
Distributed, interacting collection of SNMP entities SNMP entity implements a portion of the SNMP capability:
It acts either as an agent or manager or both A collection of modules interacting with each other to provide services
OTHERNOTIFICATIONORIGINATOR
COMMANDRESPONDER
COMMANDGENERATOR
NOTIFICATIONRECEIVER
PROXYFORWARDER
SNMP APPLICATIONS
SNMP ENGINE
MESSAGE PROCESSING
SUBSYSTEMDISPATCHERSECURITY
SUBSYSTEMACCESS CONTROL
SUBSYSTEM
SNMP ENTITY
OTHER
SNMP Architecture
Advantages:
The role of SNMP entity is determined by the modules implemented in that entityo Certain set of modules are required for agent, while
a different set is required for a manager
Security subsystem provides services such as authentication and privacy of messageso Multiple security models can coexist
Set of authorization services an application can use for checking access rightso Access Control
SNMP Architecture-Manager
NOTIFICATIONRECEIVER
COMMANDGENERATOR
PDUDISPATCHER
USER BASEDSECURITY MODEL
OTHERSECURITY MODEL
SECURITY SUBSYSTEM
SNMPv1
SNMPv2C
SNMPv3
OTHER
MESSAGE PROCESSINGSUBSYSTEM
MESSAGEDISPATCHER
TRANSPORTMAPPINGS
NOTIFICATIONORIGINATOR
SECURITY MODELCOMMUNITY BASED
SNMPv3 Architecture-Manager Command Generator Application
o Monitor and manipulate management data at remote agentso Make use of SNMPv1,v2 PDUs: Get, GetNext, GetBulk, etc.
Notification Originator Application Initiates messages, such as InformRequest PDU
Notification Receiver Applicationo Receive messages from other managers or agentso InformRequest, SNMPv1- and SNMPv2-Traps, etc…
These applications make use of the services provided by the SNMP engine:o Get Outgoing PDUs, process them and generates SNMP
messages for transmission over the transport layero Accept incoming SNMP messages, process them, and extracts
PDUs and passes them to appropriate SNMP application
SNMPv3 Architecture-Manager
One dispatcher in an SNMP engineo Accepts PDUs from applicationso Handles multiple version messages (SNMPv1, v2, v3)o Interfaces with application modules, network, and message processing
models Three components for three functions
Transport mapper delivers messages over the transport protocol Routes messages between network and appropriate module of
MPS PDU dispatcher handles messages between application and MPS
SNMP Engine (identified by snmpEngineID)
DispatcherMessage
ProcessingSubsystem
SecuritySubsystem
SNMPv3 Architecture-Manager
Accepts outgoing PDUs from Dispatcher, attach appropriate header, and return message to Dispatcher
Accepts incoming messages, process each message header, and return the enclosed PDU to the Dispatcher
Contains one or more Message Processing Models, each for each SNMP version
SNMP version identified in the header
SNMP Engine (identified by snmpEngineID)
MessageProcessingSubsystem
SecuritySubsystem
Dispatcher
SNMPv3 Architecture-Manager
Security subsystems perform authentication and encryption functions for each outgoing/incoming message
Outgoing PDUs may be encrypted and authentication codes generated and appended to the message headero The message is then returned to the MPS
Incoming messages are passed to the security subsystemo Message decryption o Messages authenticated
SNMP Engine (identified by snmpEngineID)
SecuritySubsystem
DispatcherMessage
ProcessingSubsystem
SNMPv3 Architecture-Agent
PDUDISPATCHER
SNMPv1
SNMPv2C
SNMPv3
OTHER
MESSAGE PROCESSINGSUBSYSTEM
MESSAGEDISPATCHER
TRANSPORTMAPPINGS
MANAGEMENT INFORMATION BASE
VIEW BASEDACCESS CONTROL
ACCESS CONTROL SUBSYSTEM
NOTIFICATIONORIGINATOR
COMMANDRESPONDER
USER BASEDSECURITY MODEL
OTHERSECURITY MODEL
SECURITY SUBSYSTEM
Proxy ForwarderApplications
COMMUNITY BASEDSECURITY MODEL
SNMPv3 Architecture-Agent
Command Responder Applicationo Provides access to management datao Responds to incoming requests by retrieving and/or setting
managed objects and issuing Response PDU
Notification Originator Applicationo e.g., SNMPv1, v2 Trap PDU
Proxy Forwarder Application o Forwards messages between entities
Access Control Subsystemo Provides authorization services to “control access” to the MIB
for reading and setting management objectso Who can accesso What can be accessed
Terminology
SNMP Engine ID snmpEngineID -- associated with each SNMP entity
Principal principal -- person or group or application requesting services
Security Name securityName -- human readable name
Context Engine ID contextEngineID -- each entity has a unique context ID (identical to snmpEngineID)
Context Name contextName --a context associated with a managed object (for access control)
An SNMP agent can monitor more than one network element (context)
Example: SNMP Engine ID IP address
Principal John Smith Security Name Administrator
snmpEngineID
O TH ER
SNMP ENGINE
SNMP ENTITY
snmpEngineID=4
O TH ER
SNMP ENGINE
SNMP ENTITY
snmpEngineID=2
O TH ER
SNMP ENGINE
SNMP ENTITY
snmpEngineID=3
OT HE R
SNMP ENGINE
SNMP ENTITY
snmpEngineID=1
Abstract Service Interfaces
Abstract service interface is a conceptual interface between modules, independent of implementation
Defines a set of primitives o A primitive specifies the function to be performed (e.g.,
procedural call)
Primitives associated with receiving entitieso An interface defined using primitive and parameters is referred
to as “abstract service interface”
e.g., Dispatcher primitives:o Handle messages to and from applicationso registering and un-registering of application moduleso transmitting to and receiving messages from network
IN and OUT parameters
Status information / result
Dispatcher Primitives
sendPdu
Used by a command generator to send SNMP request or notification PDU to another SNMP entity
When successfully preparing the message by the Dispatcher: a sendPduHandle (unique identifier) is returned (to track any response, if
any is expected)
The application also provides transport domain/address for the PDU as well as message processing model, security model, principal, level of security, the context for this PDU, and the PDU itself
CommandGenerator
Dispatcher
AbstractService
Interface
sendPdu
AbstractService
Interface
prep
areO
utgo
ingM
essa
ge
MessageProcessing
Model
sendPduHandle/Error Indication
Dispatcher Primitives
processResponsePdu Used by Dispatcher to pass an incoming response PDU to
an application The application checks whether it is matched with a
preceding request or notification PDU by checking the sendPduHandle: Success or failure
CommandGenerator
Dispatcher
sendPdu
AbstractService
Interface
prep
areO
utgo
ingM
essa
ge
MessageProcessing
Model
sendPduHandle/errorIndication
processResponsePdu
Dispatcher Primitives
processPdu Used by Dispatcher to pass an incoming request or
notification PDU to an application (command responder) Security related information is required to generate a matching
response message The security subsystem (access control) will check whether access
is allowed and a response will be generated accordingly
returnResponsePdu Used by command responder to return an SNMP response in
response to an incoming request or notification
CommandResponder
Dispatcher
returnResponsePdu
AbstractService
Interface
prep
areR
espo
nseM
essa
ge
MessageProcessing
ModelprocessPdu
Message Processing Subsystem Primitives
prepareOutgoingMessage Prepare a message for an outgoing SNMP request or notification
PDU The IN parameter is a PDU and OUT parameter is the message Success or failure is returned
CommandGenerator
Dispatcher
sendPdu
AbstractService
Interface
prep
areO
utgo
ingM
essa
ge
MessageProcessing
Model
sendPduHandle/errorIndication
Message Processing Subsystem Primitives
prepareResponseMessage Request the preparation of a message containing an
outgoing SNMP response PDU, in response to an incoming request or notification PDU
CommandResponder
Dispatcher
returnResponsePdu
AbstractService
Interface
prep
areR
espo
nseM
essa
ge
MessageProcessing
ModelprocessPdu
Security Subsystem Primitives
generateRequestMessage Generate a “message” containing an outgoing SNMP request or
notification PDU Returns to the MPS a message (with possibly authentication and
encryption) and associated security parameters
processIncomingMessage Provide security function for incoming messages Return success or failure indicating the result of the security check If successful, a PDU is returned to the MPS
generateResponseMessage Generate a message containing outgoing SNMP response PDU in
response to incoming request or notification Returns to the MPS a message (with some authentication and encryption
applied) and associated security parameters
22
Applications
Application(s)
CommandGenerator
NotificationReceiver
ProxyForwarderSubsystem
CommandResponder
NotificationOriginator
Other
Application Example • Command generator get-request• Command responder get-response• Notification originator trap generation• Notification receiver trap processing• Proxy Forwarder get-bulk to get-next (SNMP versions only)• Other Special application
Command Generator
Network
send get-request message
receive get-response message
CommandGenerator Dispatcher
MessageProcessing
ModelSecurityModel
sendPdu
PduHandle
prepareOutgoingMessage
generateRequestMsg
processResponsePdu
prepareDataElemetsprocessIncomingMsg
CommandGenerator
DispatcherMessage
ProcessingModel
SecurityModel
Command Generator:
1)-Examine parameters from the received PDU and match/compare them with a cached copy (security model/level/name, contextName, etc.). If no match, message is discarded
2)-Check the received PDU (check request-id, etc.)
3)- if all OK, then take action
Command Responder
Network
receive get-request message
send get-response message
CommandResponder
Dispatcher
MessageProcessing
ModelSecurityModel
processPdu
processIncomingMsg
prepareDataElements
Figure 7.6 Command Responder Application
returnResponsePdu
prepareResponseMsg
generateResponseMsg
DispatcherMessage
ProcessingModel
SecurityModel
registerContextEngineID
Command Responder:
1)-examines content of request PDU. Check whether object has already registered with the responder
2)- isAccessAllowed primitive is invoked (to determine whether object can be accessed by the principal making the request)
check the security level
3)- if access permitted, prepare a response.
Scenario Diagrams
DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
Parameters
transportDomaintransportAddress
messageProcessingModel
securityModelsecurityName
securityLevel
contextEngineIDcontextName
pduVersion
PDU
expectResponse
maxSizeResponseScopedPDU
stateReferencestatusInformation
sendPduHandle
destTransportDomaindestTransportAddress
outgoingMessageoutgoingMessageLength
wholeMsgwholeMsgLength
pduType
viewTypevariableName
globalDatamaxMessageSize
securityEngineID
scopedPDU
securityParameterssecurityStateReference
Scenario Diagrams
DISPATCHER
ACCESSCONTROL
SUBSYSTEM
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
Parameters
transportDomaintransportAddress
messageProcessingModel
securityModelsecurityName
securityLevel
contextEngineIDcontextName
pduVersion
PDU
expectResponse
maxSizeResponseScopedPDU
stateReferencestatusInformation
sendPduHandle
destTransportDomaindestTransportAddress
outgoingMessageoutgoingMessageLength
wholeMsgwholeMsgLength
pduType
viewTypevariableName
globalDatamaxMessageSize
securityEngineID
scopedPDU
securityParameterssecurityStateReference
sendPdu
APPLICATIONS
Scenario Diagrams
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
Parameters
transportDomaintransportAddress
messageProcessingModel
securityModelsecurityName
securityLevel
contextEngineIDcontextName
pduVersion
PDU
expectResponse
maxSizeResponseScopedPDU
stateReferencestatusInformation
sendPduHandle
destTransportDomaindestTransportAddress
outgoingMessageoutgoingMessageLength
wholeMsgwholeMsgLength
pduType
viewTypevariableName
globalDatamaxMessageSize
securityEngineID
scopedPDU
securityParameterssecurityStateReference
prepareOutgoingMessage
DISPATCHER
Scenario Diagrams
DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
SECURITYSUBSYSTEM DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
Parameters
transportDomaintransportAddress
messageProcessingModel
securityModelsecurityName
securityLevel
contextEngineIDcontextName
pduVersion
PDU
expectResponse
maxSizeResponseScopedPDU
stateReferencestatusInformation
sendPduHandle
destTransportDomaindestTransportAddress
outgoingMessageoutgoingMessageLength
wholeMsgwholeMsgLength
pduType
viewTypevariableName
globalDatamaxMessageSize
securityEngineID
scopedPDU
securityParameterssecurityStateReference
generateRequestMsg
MESSAGEPROCESSINGSUBSYSTEM
Scenario Diagrams
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
Parameters
transportDomaintransportAddress
messageProcessingModel
securityModelsecurityName
securityLevel
contextEngineIDcontextName
pduVersion
PDU
expectResponse
maxSizeResponseScopedPDU
stateReferencestatusInformation
sendPduHandle
destTransportDomaindestTransportAddress
outgoingMessageoutgoingMessageLength
wholeMsgwholeMsgLength
pduType
viewTypevariableName
globalDatamaxMessageSize
securityEngineID
scopedPDU
securityParameterssecurityStateReference
send and receive
DISPATCHER
Scenario Diagrams
DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
Parameters
transportDomaintransportAddress
messageProcessingModel
securityModelsecurityName
securityLevel
contextEngineIDcontextName
pduVersion
PDU
expectResponse
maxSizeResponseScopedPDU
stateReferencestatusInformation
sendPduHandle
destTransportDomaindestTransportAddress
outgoingMessageoutgoingMessageLength
wholeMsgwholeMsgLength
pduType
viewTypevariableName
globalDatamaxMessageSize
securityEngineID
scopedPDU
securityParameterssecurityStateReference
prepareDataElements
DISPATCHER
Scenario Diagrams
DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
SECURITYSUBSYSTEM
Parameters
transportDomaintransportAddress
messageProcessingModel
securityModelsecurityName
securityLevel
contextEngineIDcontextName
pduVersion
PDU
expectResponse
maxSizeResponseScopedPDU
stateReferencestatusInformation
sendPduHandle
destTransportDomaindestTransportAddress
outgoingMessageoutgoingMessageLength
wholeMsgwholeMsgLength
pduType
viewTypevariableName
globalDatamaxMessageSize
securityEngineID
scopedPDU
securityParameterssecurityStateReference
processIncomingMsg
MESSAGEPROCESSINGSUBSYSTEM
Scenario Diagrams
DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
Parameters
transportDomaintransportAddress
messageProcessingModel
securityModelsecurityName
securityLevel
contextEngineIDcontextName
pduVersion
PDU
expectResponse
maxSizeResponseScopedPDU
stateReferencestatusInformation
sendPduHandle
destTransportDomaindestTransportAddress
outgoingMessageoutgoingMessageLength
wholeMsgwholeMsgLength
pduType
viewTypevariableName
globalDatamaxMessageSize
securityEngineID
scopedPDU
securityParameterssecurityStateReference
processPdu
DISPATCHER
Scenario Diagrams
DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM DISPATCHER
ACCESSCONTROL
SUBSYSTEM
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
Parameters
transportDomaintransportAddress
messageProcessingModel
securityModelsecurityName
securityLevel
contextEngineIDcontextName
pduVersion
PDU
expectResponse
maxSizeResponseScopedPDU
stateReferencestatusInformation
sendPduHandle
destTransportDomaindestTransportAddress
outgoingMessageoutgoingMessageLength
wholeMsgwholeMsgLength
pduType
viewTypevariableName
globalDatamaxMessageSize
securityEngineID
scopedPDU
securityParameterssecurityStateReference
isAccessAllowed
APPLICATIONS
Scenario Diagrams
DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM DISPATCHER
ACCESSCONTROL
SUBSYSTEM
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
Parameters
transportDomaintransportAddress
messageProcessingModel
securityModelsecurityName
securityLevel
contextEngineIDcontextName
pduVersion
PDU
expectResponse
maxSizeResponseScopedPDU
stateReferencestatusInformation
sendPduHandle
destTransportDomaindestTransportAddress
outgoingMessageoutgoingMessageLength
wholeMsgwholeMsgLength
pduType
viewTypevariableName
globalDatamaxMessageSize
securityEngineID
scopedPDU
securityParameterssecurityStateReference
returnResponsePdu
APPLICATIONS
Scenario Diagrams
DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
Parameters
transportDomaintransportAddress
messageProcessingModel
securityModelsecurityName
securityLevel
contextEngineIDcontextName
pduVersion
PDU
expectResponse
maxSizeResponseScopedPDU
stateReferencestatusInformation
sendPduHandle
destTransportDomaindestTransportAddress
outgoingMessageoutgoingMessageLength
wholeMsgwholeMsgLength
pduType
viewTypevariableName
globalDatamaxMessageSize
securityEngineID
scopedPDU
securityParameterssecurityStateReference
prepareResponseMessage
DISPATCHER
Scenario Diagrams
DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
SECURITYSUBSYSTEM
Parameters
transportDomaintransportAddress
messageProcessingModel
securityModelsecurityName
securityLevel
contextEngineIDcontextName
pduVersion
PDU
expectResponse
maxSizeResponseScopedPDU
stateReferencestatusInformation
sendPduHandle
destTransportDomaindestTransportAddress
outgoingMessageoutgoingMessageLength
wholeMsgwholeMsgLength
pduType
viewTypevariableName
globalDatamaxMessageSize
securityEngineID
scopedPDU
securityParameterssecurityStateReference
generateResponseMsg
MESSAGEPROCESSINGSUBSYSTEM
Scenario Diagrams
DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
Parameters
transportDomaintransportAddress
messageProcessingModel
securityModelsecurityName
securityLevel
contextEngineIDcontextName
pduVersion
PDU
expectResponse
maxSizeResponseScopedPDU
stateReferencestatusInformation
sendPduHandle
destTransportDomaindestTransportAddress
outgoingMessageoutgoingMessageLength
wholeMsgwholeMsgLength
pduType
viewTypevariableName
globalDatamaxMessageSize
securityEngineID
scopedPDU
securityParameterssecurityStateReference
send and receive
DISPATCHER
Scenario Diagrams
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
Parameters
transportDomaintransportAddress
messageProcessingModel
securityModelsecurityName
securityLevel
contextEngineIDcontextName
pduVersion
PDU
expectResponse
maxSizeResponseScopedPDU
stateReferencestatusInformation
sendPduHandle
destTransportDomaindestTransportAddress
outgoingMessageoutgoingMessageLength
wholeMsgwholeMsgLength
pduType
viewTypevariableName
globalDatamaxMessageSize
securityEngineID
scopedPDU
securityParameterssecurityStateReference
prepareDataElements
DISPATCHER
Scenario Diagrams
DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
SECURITYSUBSYSTEM DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
Parameters
transportDomaintransportAddress
messageProcessingModel
securityModelsecurityName
securityLevel
contextEngineIDcontextName
pduVersion
PDU
expectResponse
maxSizeResponseScopedPDU
stateReferencestatusInformation
sendPduHandle
destTransportDomaindestTransportAddress
outgoingMessageoutgoingMessageLength
wholeMsgwholeMsgLength
pduType
viewTypevariableName
globalDatamaxMessageSize
securityEngineID
scopedPDU
securityParameterssecurityStateReference
processIncomingMsg
MESSAGEPROCESSINGSUBSYSTEM
Scenario Diagrams
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM DISPATCHER
ACCESSCONTROL
SUBSYSTEM
APPLICATIONS
MESSAGEPROCESSINGSUBSYSTEM
SECURITYSUBSYSTEM
Parameters
transportDomaintransportAddress
messageProcessingModel
securityModelsecurityName
securityLevel
contextEngineIDcontextName
pduVersion
PDU
expectResponse
maxSizeResponseScopedPDU
stateReferencestatusInformation
sendPduHandle
destTransportDomaindestTransportAddress
outgoingMessageoutgoingMessageLength
wholeMsgwholeMsgLength
pduType
viewTypevariableName
globalDatamaxMessageSize
securityEngineID
scopedPDU
securityParameterssecurityStateReference
processResponsePdu
DISPATCHER
Message Format
VersionGlobal/Header
Data
SecurityParameters
Plaintext / EncryptedscopedPDU Data
MessageID
MessageMax. Size
MessageFlag
MessageSecurityModel
Header Data
ContextEngine ID
ContextName
Data
scopedPDU
AuthoritativeEngine ID
AuthoritativeEngine Boots
AuthoritativeEngine Time
User Name
AuthenticationParameters
PrivacyParameters
Security Parameters
Whole Message
1 SNMPv12 SNMPv23 SNMPv3
reportableFlagprivFlagauthFlag
Time synch. between entities to avoid message replay and achieve timeliness
Message FormatField Object name Description
Version msgVersion SNMP version number of the message format
Message ID msgID Administrative ID associated with the message
Message Max. Size msgMaxSize Maximum size supported by the sender
Message flags msgFlags Bit fields identifying report, authentication, and privacy of the
message
Message Security Model
msgSecurityModel Security model used for the message; concurrent multiple models allowed
Security Parameters (See Table 7.8)
msgSecurityParameters Security parameters used for communication between sending and
receiving security modules
Plaintext/Encrypted scopedPDU Data
scopedPduData Choice of plaintext or encrypted scopedPDU; scopedPDU uniquely
identifies context and PDU
Context Engine ID contextEngineID Unique ID of a context (managed entity) with a context name realized by
an SNMP entity
Context Name contextName Name of the context (managed entity)
PDU data Contains unencrypted PDU
43See p. 304
Security Threats
Modification of Information an entity may alter in-transit SNMP
messages generated on behalf of an authorized principal in such a way as to effect unauthorized management operations, including falsifying the value of an object
Masquerade management operations not
authorized for some entity may be attempted by assuming the identity of another entity that has the appropriate authorizations
ManagementEntity A
ManagementEntity B
Modification of informationMasquerade
Message stream modification
Disclosure
Security Threats
Message Stream Modification SNMP is typically based upon a
connectionless transport service. Messages may be maliciously re-ordered, delayed or replayed, in order to effect unauthorized management operations. o For example, a message to reboot
a system could be copied and replayed later
Disclosure Eavesdropping or intercepting on
the exchanges between SNMP engines
ManagementEntity A
ManagementEntity B
Modification of informationMasquerade
Message stream modification
Disclosure
Security Threats
SNMPv3 is not intended to secure against these two threats:
Denial of Service: An attacker may prevent
exchanges between manager and agent DOS are indistinguishable from
network element failures DOS may disrupt all services (not
just those pertaining to NM)
Traffic Analysis: An attacker may observe the
general pattern of traffic between managers and agents
ManagementEntity A
ManagementEntity B
Modification of informationMasquerade
Message stream modification
Disclosure
Security Model Goals
o Data Integrity (Authentication)
o Authentication
o Message redirection/re-ordering/delay/replay
o Data encryption/decryption
Security Model
The Security model authenticates and forwards incoming and outgoing messages to the MPM
3 different moduleso Authentication moduleo Privacy moduleo Timeliness module
Security Subsystem
MessageProcessing
Model
AuthenticationModule
PrivacyModule
TimelinessModule
Data Integrity
Data Origin Authentication
Data Confidentiality
Message Timeliness &Limited Replay Protection
Authentication Module
Data integrityo message authentication at sender and validation at receivero Ensure that a message is not modified by an unauthorized intrudero Authentication protocols: HMAC-MD5-96 / HMAC-SHA-96
Data origin authenticationo Check the identity of a user on whose behalf a message is sento Append to the message a unique Identifier associated with
authoritativeauthoritative SNMP engine
Security Subsystem
MessageProcessing
Model
AuthenticationModule
PrivacyModule
TimelinessModule
Data Integrity
Data Origin Authentication
Data Confidentiality
Message Timeliness &Limited Replay Protection
Privacy Module
Data confidentiality ensures that data is not made available to unauthorized users or entities
Encryption is applied at the sender and decryption at receiver (CBC-DES)
Security Subsystem
MessageProcessing
Model
AuthenticationModule
PrivacyModule
TimelinessModule
Data Integrity
Data Origin Authentication
Data Confidentiality
Message Timeliness &Limited Replay Protection
Timeliness Module
Prevent message redirection, delay and replay
Configure a receiver window for accepting message (e.g., 150 s for SNMPv3)
Three objects: snmpEngineIP, snmpEngineBoots, snmpEngineTime
Security Subsystem
MessageProcessing
Model
AuthenticationModule
PrivacyModule
TimelinessModule
Data Integrity
Data Origin Authentication
Data Confidentiality
Message Timeliness &Limited Replay Protection
Authoritative vs. non-authoritative engine
Responsibility of Authoritative engineo Unique SNMP engine IDo Time-stamp (a clock maintained
by the authoritative engine)
Non-authoritative engine should keep a table of the time-stamp and authoritative engine IDo Synchronize its clock with regard
to that of the authoritative engine
Non-Authoritative Engine(NMS)
Non-Authoritative Engine(NMS)
Authoritative Engine(Agent)
Authoritative Engine(Agent)
User-based Security Model (USM) USM primitives across abstract service
interfaceso Authentication service primitives
o authenticateOutgoingMsgo authenticateIncomingMsg
o Privacy Serviceso encryptData // outgoing PDUo decryptData // incoming PDU
User-based Security Model (USM)
Security Subsystem
PrivacyModule
scopedPDU
Encryption keyUser-based
SecurityModel
EncryptedscopedPDU
Privacyparameters
AuthenticationModule
Whole Message
Authentication key
AuthenticatedWhole Message
Privacy and Authentication Service for Outgoing Message
MessageProcessing
Model
MPM Information
Header data
Security data
scopedPDU
(Authenticated/encrypted)whole message
Whole message length
Security Parameters
User-based Security Model (USM)
USM invokes privacy module w/ encryption key and scopedPDU
Privacy module returns privacy parameters and encrypted scopedPDU
USM then invokes the authentication module w/authentication key and whole message and receives authenticated whole message
Security Subsystem
PrivacyModule
scopedPDU
Encryption keyUser-based
SecurityModel
EncryptedscopedPDU
Privacyparameters
AuthenticationModule
Whole Message
Authentication key
AuthenticatedWhole Message
MessageProcessing
Model
MPM Information
Header data
Security data
scopedPDU
(Authenticated/encrypted)whole message
Whole message length
Security Parameters
User-based Security Model (USM)
Processing secure incoming message reverse of secure outgoing message Authentication validation done first by the authentication module Decryption of the message done then by the privacy module
Security Subsystem
User-basedSecurityModel
MessageProcessing
Model
MPM Information
Header data
Security parameters
whole message
(Decrypted) scopedPDU PrivacyModule
Decrypt key
DecryptedscopedPDU
Privacyparameters
AuthenticationModule
Whole Message(as received from network)
Authentication key
AuthenticatedWhole Message
Authenticationparameters
Encrypted PDU
User-based Security Model (USM)
msgUserName: user or a principal on whose behalf the message is being exchanged
msgAuthenticationParameters: defined by authentication protocol
msgPrivacyParameters: type of privacy protocol used
Security Parameters and Corresponding MIB Objects
Security Parameters USM User Group Objects msgAuthoritativeEngineID snmpEngineID (under snmpEngine Group) msgAuthoritativeEngineBoots snmpEngineBoots (under snmpEngine
Group) msgAuthoritativeEngineTime snmpEngineTime (under snmpEngine Group) msgUserName usmUserName (in usmUserTable) msgAuthenticationParameters usmUserAuthProtocol (in usmUserTable) msgPrivacyParameters usmUserPrivProtocol (in usmUserTable)
SNMPv3-Next!
Background and security threats SNMPv3 Architecture SNMPv3 Applications Message Format User-based Security Model (USM)
USM Timeliness Mechanism Cryptographic Functions USM Message Processing Discovery Key Management
USM Timeliness MechanismManagement of authoritative clocks
All authoritative engines must maintain two objects:o snmpEngineBootso snmpEngineTime
Initially, both are set to 0 snmpEngineTime is incremented once per second snmpEngineBoots is incremented if the system has
rebooted or if snmpEngineTime reaches its maximum value (231 -1)
USM Timeliness MechanismSynchronization
A non-authoritative engine must remain loosely synchronized with each authoritative engine with which it communicates
A non-authoritative engine keeps a local copy of 3 variables for each authoritative engine:o snmpEngineBoots:
o Most recent value of snmpEngineBoots for the remote authoritative engine
o snmpEngineTime: o Synchronized to the authoritative engine. Between synch
events, it is incremented once per second to maintain loose synch
o latestReceivedEngineTime:o Highest value of msgAuthoritativeEngineTime.
o It protects against a replay message attacko These values are stored in a cache indexed by
snmpEngineID
USM Timeliness MechanismSynchronization (cont’d)
If message is authentic non auth. updates its local variables according to this rule:
(msgAuthoritativeEngineBoots > snmpEngineBoots) OR
[(msgAuthoritativeEngineBoots = snmpEngineBoots) AND
(msgAuthoritativeEngineTime > latestReceivedEngineTime)]
authoritative non-authoritative
msgAuthoritativeEngineBoots, msgAthoritativeEngineTime,msgAthoritativeEngineID
If two messages arrive out of order or a replay attack is underway!
USM Timeliness MechanismSynchronization (cont’d)
If an update is called for, thensnmpEngineBoots := msgAuthoritativeEngineBoots
snmpEngineTime := msgAuthoritativeEngineTime
latestReceivedEngineTime := msgAuthoritativeEngineTime
If (msgAuthoritativeEngineBoots < snmpEngineBoots) then no update occurs [Message not authentic to be discarded]
If [(msgAuthoritativeEngineBoots = snmpEngineBoots) AND
(msgAuthoritativeEngineTime < latestReceivedEngineTime)] then no update occurs [Message may be authentic but may be misordered Update of snmpEngineTime is not warranted]
USM Timeliness MechanismTimeliness checking by authoritative receiver
Ensure that messages are received within a reasonable time window (avoid delays and replays) Too small time window authentic messages may be considered
as unauthentic Too large increase vulnerability for attacks
Incoming message is considered outside the time window if the following is true :snmpEngineBoots = (231 -1) OR
msgAuthoritativeEngineBoots snmpEngineBoots ORThe value of msgAuthoritativeEngineTime differs from that of
snmpEngineTime by more than ± 150 seconds.
message is considered not authentic (discarded and error message returned)
USM Timeliness MechanismTimeliness checking by non-authoritative receiver
Incoming message is considered outside the time window if the following is true:snmpEngineBoots = (231 -1) OR
msgAuthoritativeEngineBoots < snmpEngineBoots OR
[(msgAuthoritativeEngineBoots = snmpEngineBoots) AND msgAuthoritativeEngineTime < snmpEngineTime – 150]
NOTE:
msgAuthoritativeEngineBoots > snmpEngineBoots is allowed
Cryptographic Functions-Authentication2 functions defined by USM
authentication: authKey encryption: privKey authKey and privKey are derived from the password and are not
accessible via SNMP
1- Authentication Two authentication protocols
o HMAC-MD5-96 (Message Digest)o HMAC-SHA1-96 (Secure Hash Algorithm)
HMAC: message authentication code generation from authKey A 96-bit MAC code generated and inserted in msgAuthenticationParameters
field of the message MD-5 (16-octet) and SHA1 (20-octet) are the underlying hash functions
Cryptographic Functions-Authentication Procedure:
1. Derive extendedAuthKey: Supplement authKey with 0s to get 64-byte string
2. Define ipad, opad, K1, and K2: ipad = 0x36 (00110110) repeated 64 times opad = 0x5c (01011100) repeated 64 times K1 = extendedAuthKey XOR ipad K2 = extendedAuthKey XOR opad
3. Derive HMAC by hashing algorithm used HMAC = H (K2, H (K1, wholeMsg))
Depending on whether MD-5 or SHA-1 is used, the algorithm produces a 16 (MD-5) or 20 (SHA-1)-octet length output which is truncated to produce a 12-octet MAC
67
HMAC Structure
Cryptographic Functions-Authentication
HASH FUNCTION
DATAKEY
MAC
ADD THE MESSAGE AUTHENTICATION CODE (MAC) TO THE DATAAND SEND THE RESULT
To authenticate
HASH FUNCTION
KEY
MAC
DATAUSER MAC
DATA
HASH FUNCTION
KEY
MAC
DATAUSER MAC
DATA
=?
sender receiver
Cryptographic Functions-Encryption
2- Encryption and decryption of scoped PDU
(context engine ID, context name, and PDU)
CBC - DES (Cipher Block Chaining - Data Encryption Standard) symmetric protocolo 16 octet privKey (derived from password, similar to
authKey ) is used as input to encryption protocolo First 8 octets of privKey are used as DES key (only 56 bits
LSB of each octet is ignored)
Cryptographic Functions-Encryption
CBC Modeo Last 8-octet of privKey used as pre-
initialization vector (pre-IV)o Generate salt value (8 octets):
<snmpEgineBoots || local value>
Initialization vector:
IV = salt XOR pre-IV
o Transmit salt in msgPrivacyParameters so that receiver can recover the IV
Local value: 4-octet integer, implementation dependent, modified after each use.
Cryptographic Functions-Encryption
k
IV
P1
C1
k
P2
C2
k
Pn
Cn
DES Encrypt
DES Encrypt
DES Encrypt
Cn-1
Data is divided into blocks of 64 bits each.K is shared between sender and receiver
Encryption
Cryptographic Functions-Encryption
k
IV
P1
C1
k
P2
C2
k
Pn
Cn
DES Decrypt
DES Decrypt
DES Decrypt
Cn-1
IV at the receiver is generated from the salt that is transmitted in the message
Decryption
USM Message Processing
Retrieve user information
Privacy Required?
msgPrivacyParamters NULL
Authent.Required?
msgAuthent.Paramters NULL
Encrypt scopedPDUset msgPrivacyParamters
YES
NO
Compute MACset msgAuthent.Paramters
YES
Message Transmission
Security name of principalAuth. snmpEngineIDDetermine security level …
NO
USM Message Processing
Retrieve msgparameters
Authent.Required?
PrivacyRequired?
Encrypt scopedPDUset msgPrivacyParamters
YES
NO
YES
Message reception
Compute MACmsgAuthent.Paramters
Determine if msg is within time window
Decrypt scopedPDU
NO
security level Security modelSecurity name….
Time synch.Timeliness check
Discovery
The non-authoritative engine sends a Request message:securityLevel = noAuthnoPrivmsgUserName = “initial”msgAuthoritativeEngineID = nullvarBindList = null
The authoritative engine responds with:msgAuthoritativeEngineID = snmpEngineID (its own)
If authenticated communication is requiredo The non-authoritative engine establishes time synchronization with the
authoritative engineo Authoritative engine sends an Report message with its current values:
msgAuthoritativeEngineBoots = snmpEngineBoots msgAuthoritativeEngineTime = snmpEngineTime
Key Management
Authentication and privacy keys are required
A principal (i.e., NMS) should deploy or use only one auth. key and one priv. key.
Keys are stored for the user’s password Password: human readable, not
easy guessed Keys are not accessible via
SNMP and are not stored in the MIB
Password to key generation
1)- Repeat the psswd to generate 220 bytes digest0
2)-
digest1 = Hash (digest0)
digest1 is 16-octet (MD-5) or 20-octet (SHA-1)
authKey is digest1
NOTE :: A single password can be used (authKey and privKey are the same) or 2 passwords for 2 different keys
Key Localization
A localized key is a secret key shared between a user and one authoritative SNMP Engine Hence, a user can communicate with many agents but maintains
only one key (i.e., only one password)
User 1
User 2
(authKey1_1, privKey1_1)
(authKey1_2, privKey1_2)
Agent 1
User 1
User 4
(authKey2_1, privKey2_1)
(authKey2_4, privKey2_4)
Agent 2
If compromised, other keys are not!If this agent compromised, only its keys are compromised. Other agents are safe.
Generating localized Keys
password Take Hashof expanded
password string
Take Hashof user key and
Remote Engine ID
Take Hashof user key and
Remote Engine ID
Take Hashof user key and
Remote Engine ID
User Key
(digest1)
Localized Key
digest2
Localized key
Localized key
Localized keys are initially configured in a secure way (could be manual!)
Key Update
To enhance security, Keys are to be updated from time to time: keyOld keyNew
Requestor:1)- Generate random2)- Compute: digest = Hash ( keyOld || random )3)- delta = digest XOR keyNew4)- protocolKeyChange = ( random || delta)Send a message setRequest ( protocolKeyChange )
Receiver:1)- compute digest = Hash( keyOld || random)2)- compute keyNew = digest XOR delta NOTE: digest XOR delta = digest XOR (digest XOR keyNew) = keyNew
Since an attacker does not know keyOld, the update of the key is safe
Access Control
Agent can validate sending sources and their access privilege for command requests.
Step following Authentication Maintain a local database contains access rights
and policies
MIB VIEW Allowed Operations
Allowed managers Required Level of Security
Interface Table
SET John Authentication, Encryption
Interface Table
GET/GETNEXT John, Paul Authentication
Systems Group
GET/GETNEXT Georges None
Access Control
(read, write, or send notification)
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