Class: NETSNMP::Message

Inherits:
Object
  • Object
show all
Includes:
Loggable
Defined in:
lib/netsnmp/message.rb

Overview

Factory for the SNMP v3 Message format

Constant Summary collapse

PRIVNONE = 
OpenSSL::ASN1::OctetString.new("")
MSG_MAX_SIZE = 
OpenSSL::ASN1::Integer.new(65507).with_label(:max_message_size)
MSG_SECURITY_MODEL =

usmSecurityModel

OpenSSL::ASN1::Integer.new(3).with_label(:security_model)
MSG_VERSION = 
OpenSSL::ASN1::Integer.new(3).with_label(:message_version)
MSG_REPORTABLE = 
4

Constants included from Loggable

Loggable::DEBUG, Loggable::DEBUG_LEVEL

Instance Method Summary collapse

Methods included from Loggable

#initialize_logger

Constructor Details

#initialize(**args) ⇒ Message

Returns a new instance of Message.



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# File 'lib/netsnmp/message.rb', line 16

def initialize(**args)
  initialize_logger(**args)
end

Instance Method Details

#decode(stream, security_parameters:) ⇒ NETSNMP::ScopedPDU

Returns the decoded PDU.

Parameters:

  • payload (String) —

    of an snmp v3 message which can be decoded

  • security_parameters (NETSMP::SecurityParameters, #decode) —

    knowns how to decode the stream

Returns:



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# File 'lib/netsnmp/message.rb', line 29

def decode(stream, security_parameters:)
  log { "received encoded V3 message" }
  log { Hexdump.dump(stream) }
  asn_tree = OpenSSL::ASN1.decode(stream).with_label(:v3_message)

  version, headers, sec_params, pdu_payload = asn_tree.value
  version.with_label(:message_version)
  headers.with_label(:headers)
  sec_params.with_label(:security_params)
  pdu_payload.with_label(:pdu)

  _, _, message_flags, = headers.value

  # get last byte
  # discard the left-outermost bits and keep the remaining two
  security_level = message_flags.with_label(:message_flags).value.unpack("C*").last & 3

  sec_params_asn = OpenSSL::ASN1.decode(sec_params.value).with_label(:security_params)

  engine_id, engine_boots, engine_time, username, auth_param, priv_param = sec_params_asn.value
  engine_id.with_label(:engine_id)
  engine_boots.with_label(:engine_boots)
  engine_time.with_label(:engine_time)
  username.with_label(:username)
  auth_param.with_label(:auth_param)
  priv_param.with_label(:priv_param)

  log(level: 2) { asn_tree.to_hex }
  log(level: 2) { sec_params_asn.to_hex }

  auth_param = auth_param.value

  engine_boots = engine_boots.value.to_i
  engine_time = engine_time.value.to_i

  encoded_pdu = security_parameters.decode(pdu_payload, salt: priv_param.value,
                                                        engine_boots: engine_boots,
                                                        engine_time: engine_time,
                                                        security_level: security_level)

  log { "received response PDU" }
  pdu = ScopedPDU.decode(encoded_pdu, auth_param: auth_param, security_level: security_level)

  log(level: 2) { pdu.to_hex }
  [pdu, engine_id.value.to_s, engine_boots, engine_time]
end

#encode(pdu, security_parameters:, engine_boots: 0, engine_time: 0) ⇒ String

Returns the byte representation of an SNMP v3 Message.

Parameters:

  • the (NETSNMP::ScopedPDU) —

    PDU to encode in the message

  • security_parameters (NETSMP::SecurityParameters, #decode) —

    knowns how to decode the stream

Returns:

  • (String) —

    the byte representation of an SNMP v3 Message



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# File 'lib/netsnmp/message.rb', line 81

def encode(pdu, security_parameters:, engine_boots: 0, engine_time: 0)
  log(level: 2) { pdu.to_hex }
  log { "encoding PDU in V3 message..." }
  scoped_pdu, salt_param = security_parameters.encode(pdu, salt: PRIVNONE,
                                                           engine_boots: engine_boots,
                                                           engine_time: engine_time)

  sec_params = OpenSSL::ASN1::Sequence.new([
                                             OpenSSL::ASN1::OctetString.new(security_parameters.engine_id).with_label(:engine_id),
                                             OpenSSL::ASN1::Integer.new(engine_boots).with_label(:engine_boots),
                                             OpenSSL::ASN1::Integer.new(engine_time).with_label(:engine_time),
                                             OpenSSL::ASN1::OctetString.new(security_parameters.username).with_label(:username),
                                             authnone(security_parameters.auth_protocol),
                                             salt_param
                                           ]).with_label(:security_params)
  log(level: 2) { sec_params.to_hex }

  message_flags = MSG_REPORTABLE | security_parameters.security_level
  message_id    = OpenSSL::ASN1::Integer.new(SecureRandom.random_number(2147483647)).with_label(:message_id)
  headers = OpenSSL::ASN1::Sequence.new([
                                          message_id,
                                          MSG_MAX_SIZE,
                                          OpenSSL::ASN1::OctetString.new([String(message_flags)].pack("h*")).with_label(:message_flags),
                                          MSG_SECURITY_MODEL
                                        ]).with_label(:headers)

  encoded = OpenSSL::ASN1::Sequence([
                                      MSG_VERSION,
                                      headers,
                                      OpenSSL::ASN1::OctetString.new(sec_params.to_der).with_label(:security_params),
                                      scoped_pdu
                                    ]).with_label(:v3_message)
  log(level: 2) { encoded.to_hex }

  encoded = encoded.to_der
  log { Hexdump.dump(encoded) }
  signature = security_parameters.sign(encoded)
  if signature
    log { "signing V3 message..." }
    auth_salt = OpenSSL::ASN1::OctetString.new(signature).with_label(:auth)
    log(level: 2) { auth_salt.to_hex }
    none_der = authnone(security_parameters.auth_protocol).to_der
    encoded[encoded.index(none_der), none_der.size] = auth_salt.to_der
    log { Hexdump.dump(encoded) }
  end
  encoded
end

#verify(stream, auth_param, security_level, security_parameters:) ⇒ Object 



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# File 'lib/netsnmp/message.rb', line 20

def verify(stream, auth_param, security_level, security_parameters:)
  security_parameters.verify(stream.sub(auth_param, authnone(security_parameters.auth_protocol).value), auth_param, security_level: security_level)
end