Module: NETSNMP::Message

Defined in:
lib/netsnmp/message.rb

Overview

Factory for the SNMP v3 Message format

Constant Summary collapse

AUTHNONE = 
OpenSSL::ASN1::OctetString.new("\x00" * 12)
PRIVNONE = 
OpenSSL::ASN1::OctetString.new("")
MSG_MAX_SIZE = 
OpenSSL::ASN1::Integer.new(65507)
MSG_SECURITY_MODEL =

usmSecurityModel

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

Class Method Summary collapse

Class 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 20

def decode(stream, security_parameters:)
  asn_tree = OpenSSL::ASN1.decode(stream)
  _version, _headers, sec_params, pdu_payload = asn_tree.value

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

  engine_id, engine_boots, engine_time, _username, auth_param, priv_param = sec_params_asn.map(&:value)

  # validate_authentication
  security_parameters.verify(stream.sub(auth_param, AUTHNONE.value), auth_param)

  engine_boots = engine_boots.to_i
  engine_time = engine_time.to_i

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

  pdu = ScopedPDU.decode(encoded_pdu)
  [pdu, engine_id, 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 47

def encode(pdu, security_parameters:, engine_boots: 0, engine_time: 0)
  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),
                                             OpenSSL::ASN1::Integer.new(engine_boots),
                                             OpenSSL::ASN1::Integer.new(engine_time),
                                             OpenSSL::ASN1::OctetString.new(security_parameters.username),
                                             AUTHNONE,
                                             salt_param
                                           ])
  message_flags = MSG_REPORTABLE | security_parameters.security_level
  message_id    = OpenSSL::ASN1::Integer.new(SecureRandom.random_number(2147483647))
  headers = OpenSSL::ASN1::Sequence.new([
                                          message_id, MSG_MAX_SIZE,
                                          OpenSSL::ASN1::OctetString.new([String(message_flags)].pack("h*")),
                                          MSG_SECURITY_MODEL
                                        ])

  encoded = OpenSSL::ASN1::Sequence([
                                      MSG_VERSION,
                                      headers,
                                      OpenSSL::ASN1::OctetString.new(sec_params.to_der),
                                      scoped_pdu
                                    ]).to_der
  signature = security_parameters.sign(encoded)
  if signature
    auth_salt = OpenSSL::ASN1::OctetString.new(signature)
    encoded.sub!(AUTHNONE.to_der, auth_salt.to_der)
  end
  encoded
end