@vostro/net-snmp/index.js

JavaScript implementation of the Simple Network Management Protocol (SNMP)

// Copyright 2013 Stephen Vickers <stephen.vickers.sv@gmail.com>

var ber = require ("asn1-ber").Ber;
var smartbuffer = require ("smart-buffer");
var dgram = require ("dgram");
var net = require ("net");
var events = require ("events");
var util = require ("util");
var crypto = require ("crypto");
var mibparser = require ("./lib/mib");
var DEBUG = false;

var MAX_INT32 = 2147483647;

function debug (line) {
	if ( DEBUG ) {
		console.debug (line);
	}
}

/*****************************************************************************
 ** Constants
 **/


function _expandConstantObject (object) {
	var keys = [];
	for (var key in object)
		keys.push (key);
	for (var i = 0; i < keys.length; i++)
		object[object[keys[i]]] = parseInt (keys[i]);
}

var ErrorStatus = {
	0: "NoError",
	1: "TooBig",
	2: "NoSuchName",
	3: "BadValue",
	4: "ReadOnly",
	5: "GeneralError",
	6: "NoAccess",
	7: "WrongType",
	8: "WrongLength",
	9: "WrongEncoding",
	10: "WrongValue",
	11: "NoCreation",
	12: "InconsistentValue",
	13: "ResourceUnavailable",
	14: "CommitFailed",
	15: "UndoFailed",
	16: "AuthorizationError",
	17: "NotWritable",
	18: "InconsistentName"
};

_expandConstantObject (ErrorStatus);

var ObjectType = {
	1: "Boolean",
	2: "Integer",
	4: "OctetString",
	5: "Null",
	6: "OID",
	64: "IpAddress",
	65: "Counter",
	66: "Gauge",
	67: "TimeTicks",
	68: "Opaque",
	70: "Counter64",
	128: "NoSuchObject",
	129: "NoSuchInstance",
	130: "EndOfMibView"
};

_expandConstantObject (ObjectType);

// ASN.1
ObjectType.INTEGER = ObjectType.Integer;
ObjectType["OCTET STRING"] = ObjectType.OctetString;
ObjectType["OBJECT IDENTIFIER"] = ObjectType.OID;
// SNMPv2-SMI
ObjectType.Integer32 = ObjectType.Integer;
ObjectType.Counter32 = ObjectType.Counter;
ObjectType.Gauge32 = ObjectType.Gauge;
ObjectType.Unsigned32 = ObjectType.Gauge32;
// SNMPv2-TC
ObjectType.AutonomousType = ObjectType["OBJECT IDENTIFIER"];
ObjectType.DateAndTime = ObjectType["OCTET STRING"];
ObjectType.DisplayString = ObjectType["OCTET STRING"];
ObjectType.InstancePointer = ObjectType["OBJECT IDENTIFIER"];
ObjectType.MacAddress = ObjectType["OCTET STRING"];
ObjectType.PhysAddress = ObjectType["OCTET STRING"];
ObjectType.RowPointer = ObjectType["OBJECT IDENTIFIER"];
ObjectType.RowStatus = ObjectType.INTEGER;
ObjectType.StorageType = ObjectType.INTEGER;
ObjectType.TestAndIncr = ObjectType.INTEGER;
ObjectType.TimeStamp = ObjectType.TimeTicks;
ObjectType.TruthValue = ObjectType.INTEGER;
ObjectType.TAddress = ObjectType["OCTET STRING"];
ObjectType.TDomain = ObjectType["OBJECT IDENTIFIER"];
ObjectType.VariablePointer = ObjectType["OBJECT IDENTIFIER"];

var PduType = {
	160: "GetRequest",
	161: "GetNextRequest",
	162: "GetResponse",
	163: "SetRequest",
	164: "Trap",
	165: "GetBulkRequest",
	166: "InformRequest",
	167: "TrapV2",
	168: "Report"
};

_expandConstantObject (PduType);

var TrapType = {
	0: "ColdStart",
	1: "WarmStart",
	2: "LinkDown",
	3: "LinkUp",
	4: "AuthenticationFailure",
	5: "EgpNeighborLoss",
	6: "EnterpriseSpecific"
};

_expandConstantObject (TrapType);

var SecurityLevel = {
	1: "noAuthNoPriv",
	2: "authNoPriv",
	3: "authPriv"
};

_expandConstantObject (SecurityLevel);

var AuthProtocols = {
	"1": "none",
	"2": "md5",
	"3": "sha"
};

_expandConstantObject (AuthProtocols);

var PrivProtocols = {
	"1": "none",
	"2": "des",
	"4": "aes"
};

_expandConstantObject (PrivProtocols);

var UsmStatsBase = "1.3.6.1.6.3.15.1.1";

var UsmStats = {
	"1": "Unsupported Security Level",
	"2": "Not In Time Window",
	"3": "Unknown User Name",
	"4": "Unknown Engine ID",
	"5": "Wrong Digest (incorrect password, community or key)",
	"6": "Decryption Error"
};

_expandConstantObject (UsmStats);

var MibProviderType = {
	"1": "Scalar",
	"2": "Table"
};

_expandConstantObject (MibProviderType);

var Version1 = 0;
var Version2c = 1;
var Version3 = 3;

var Version = {
	"1": Version1,
	"2c": Version2c,
	"3": Version3
};

var AgentXPduType = {
	1: "Open",
	2: "Close",
	3: "Register",
	4: "Unregister",
	5: "Get",
	6: "GetNext",
	7: "GetBulk",
	8: "TestSet",
	9: "CommitSet",
	10: "UndoSet",
	11: "CleanupSet",
	12: "Notify",
	13: "Ping",
	14: "IndexAllocate",
	15: "IndexDeallocate",
	16: "AddAgentCaps",
	17: "RemoveAgentCaps",
	18: "Response"
};

_expandConstantObject (AgentXPduType);

/*****************************************************************************
 ** Exception class definitions
 **/

function ResponseInvalidError (message) {
	this.name = "ResponseInvalidError";
	this.message = message;
	Error.captureStackTrace(this, ResponseInvalidError);
}
util.inherits (ResponseInvalidError, Error);

function RequestInvalidError (message) {
	this.name = "RequestInvalidError";
	this.message = message;
	Error.captureStackTrace(this, RequestInvalidError);
}
util.inherits (RequestInvalidError, Error);

function RequestFailedError (message, status) {
	this.name = "RequestFailedError";
	this.message = message;
	this.status = status;
	Error.captureStackTrace(this, RequestFailedError);
}
util.inherits (RequestFailedError, Error);

function RequestTimedOutError (message) {
	this.name = "RequestTimedOutError";
	this.message = message;
	Error.captureStackTrace(this, RequestTimedOutError);
}
util.inherits (RequestTimedOutError, Error);

/*****************************************************************************
 ** OID and varbind helper functions
 **/

function isVarbindError (varbind) {
	return !!(varbind.type == ObjectType.NoSuchObject
	|| varbind.type == ObjectType.NoSuchInstance
	|| varbind.type == ObjectType.EndOfMibView);
}

function varbindError (varbind) {
	return (ObjectType[varbind.type] || "NotAnError") + ": " + varbind.oid;
}

function oidFollowsOid (oidString, nextString) {
	var oid = {str: oidString, len: oidString.length, idx: 0};
	var next = {str: nextString, len: nextString.length, idx: 0};
	var dotCharCode = ".".charCodeAt (0);

	function getNumber (item) {
		var n = 0;
		if (item.idx >= item.len)
			return null;
		while (item.idx < item.len) {
			var charCode = item.str.charCodeAt (item.idx++);
			if (charCode == dotCharCode)
				return n;
			n = (n ? (n * 10) : n) + (charCode - 48);
		}
		return n;
	}

	while (1) {
		var oidNumber = getNumber (oid);
		var nextNumber = getNumber (next);

		if (oidNumber !== null) {
			if (nextNumber !== null) {
				if (nextNumber > oidNumber) {
					return true;
				} else if (nextNumber < oidNumber) {
					return false;
				}
			} else {
				return true;
			}
		} else {
			return true;
		}
	}
}

function oidInSubtree (oidString, nextString) {
	var oid = oidString.split (".");
	var next = nextString.split (".");

	if (oid.length > next.length)
		return false;

	for (var i = 0; i < oid.length; i++) {
		if (next[i] != oid[i])
			return false;
	}

	return true;
}

/**
 ** Some SNMP agents produce integers on the wire such as 00 ff ff ff ff.
 ** The ASN.1 BER parser we use throws an error when parsing this, which we
 ** believe is correct.  So, we decided not to bother the "asn1" developer(s)
 ** with this, instead opting to work around it here.
 **
 ** If an integer is 5 bytes in length we check if the first byte is 0, and if so
 ** simply drop it and parse it like it was a 4 byte integer, otherwise throw
 ** an error since the integer is too large.
 **/

function readInt (buffer) {
	return readUint (buffer, true);
}

function readIpAddress (buffer) {
	var bytes = buffer.readString (ObjectType.IpAddress, true);
	if (bytes.length != 4)
		throw new ResponseInvalidError ("Length '" + bytes.length
				+ "' of IP address '" + bytes.toString ("hex")
				+ "' is not 4");
	var value = bytes[0] + "." + bytes[1] + "." + bytes[2] + "." + bytes[3];
	return value;
}

function readUint (buffer, isSigned) {
	buffer.readByte ();
	var length = buffer.readByte ();
	var value = 0;
	var signedBitSet = false;

	if (length > 5) {
		 throw new RangeError ("Integer too long '" + length + "'");
	} else if (length == 5) {
		if (buffer.readByte () !== 0)
			throw new RangeError ("Integer too long '" + length + "'");
		length = 4;
	}

	for (var i = 0; i < length; i++) {
		value *= 256;
		value += buffer.readByte ();

		if (isSigned && i <= 0) {
			if ((value & 0x80) == 0x80)
				signedBitSet = true;
		}
	}
	
	if (signedBitSet)
		value -= (1 << (i * 8));

	return value;
}

function readUint64 (buffer) {
	var value = buffer.readString (ObjectType.Counter64, true);

	return value;
}

function readVarbindValue (buffer, type) {
	var value;
	if (type == ObjectType.Boolean) {
		value = buffer.readBoolean ();
	} else if (type == ObjectType.Integer) {
		value = readInt (buffer);
	} else if (type == ObjectType.OctetString) {
		value = buffer.readString (null, true);
	} else if (type == ObjectType.Null) {
		buffer.readByte ();
		buffer.readByte ();
		value = null;
	} else if (type == ObjectType.OID) {
		value = buffer.readOID ();
	} else if (type == ObjectType.IpAddress) {
		value = readIpAddress (buffer);
	} else if (type == ObjectType.Counter) {
		value = readUint (buffer);
	} else if (type == ObjectType.Gauge) {
		value = readUint (buffer);
	} else if (type == ObjectType.TimeTicks) {
		value = readUint (buffer);
	} else if (type == ObjectType.Opaque) {
		value = buffer.readString (ObjectType.Opaque, true);
	} else if (type == ObjectType.Counter64) {
		value = readUint64 (buffer);
	} else if (type == ObjectType.NoSuchObject) {
		buffer.readByte ();
		buffer.readByte ();
		value = null;
	} else if (type == ObjectType.NoSuchInstance) {
		buffer.readByte ();
		buffer.readByte ();
		value = null;
	} else if (type == ObjectType.EndOfMibView) {
		buffer.readByte ();
		buffer.readByte ();
		value = null;
	} else {
		throw new ResponseInvalidError ("Unknown type '" + type
				+ "' in response");
	}
	return value;
}

function readVarbinds (buffer, varbinds) {
	buffer.readSequence ();

	while (1) {
		buffer.readSequence ();
		if ( buffer.peek () != ObjectType.OID )
			break;
		var oid = buffer.readOID ();
		var type = buffer.peek ();

		if (type == null)
			break;

		var value = readVarbindValue (buffer, type);

		varbinds.push ({
			oid: oid,
			type: type,
			value: value
		});
	}
}

function writeUint (buffer, type, value) {
	var b = Buffer.alloc (4);
	b.writeUInt32BE (value, 0);
	buffer.writeBuffer (b, type);
}

function writeUint64 (buffer, value) {
	buffer.writeBuffer (value, ObjectType.Counter64);
}

function writeVarbinds (buffer, varbinds) {
	buffer.startSequence ();
	for (var i = 0; i < varbinds.length; i++) {
		buffer.startSequence ();
		buffer.writeOID (varbinds[i].oid);

		if (varbinds[i].type && varbinds[i].hasOwnProperty("value")) {
			var type = varbinds[i].type;
			var value = varbinds[i].value;

			switch ( type ) {
				case ObjectType.Boolean:
					buffer.writeBoolean (value ? true : false);
					break;
				case ObjectType.Integer: // also Integer32
					buffer.writeInt (value);
					break;
				case ObjectType.OctetString:
					if (typeof value == "string")
						buffer.writeString (value);
					else
						buffer.writeBuffer (value, ObjectType.OctetString);
					break;
				case ObjectType.Null:
					buffer.writeNull ();
					break;
				case ObjectType.OID:
					buffer.writeOID (value);
					break;
				case ObjectType.IpAddress:
					var bytes = value.split (".");
					if (bytes.length != 4)
						throw new RequestInvalidError ("Invalid IP address '"
								+ value + "'");
					buffer.writeBuffer (Buffer.from (bytes), 64);
					break;
				case ObjectType.Counter: // also Counter32
					writeUint (buffer, ObjectType.Counter, value);
					break;
				case ObjectType.Gauge: // also Gauge32 & Unsigned32
					writeUint (buffer, ObjectType.Gauge, value);
					break;
				case ObjectType.TimeTicks:
					writeUint (buffer, ObjectType.TimeTicks, value);
					break;
				case ObjectType.Opaque:
					buffer.writeBuffer (value, ObjectType.Opaque);
					break;
				case ObjectType.Counter64:
					writeUint64 (buffer, value);
					break;
				case ObjectType.NoSuchObject:
				case ObjectType.NoSuchInstance:
				case ObjectType.EndOfMibView:
					buffer.writeByte (type);
					buffer.writeByte (0);
					break;
				default:
					throw new RequestInvalidError ("Unknown type '" + type
						+ "' in request");
			}
		} else {
			buffer.writeNull ();
		}

		buffer.endSequence ();
	}
	buffer.endSequence ();
}

/*****************************************************************************
 ** PDU class definitions
 **/

var SimplePdu = function () {
};

SimplePdu.prototype.toBuffer = function (buffer) {
	buffer.startSequence (this.type);

	buffer.writeInt (this.id);
	buffer.writeInt ((this.type == PduType.GetBulkRequest)
			? (this.options.nonRepeaters || 0)
			: 0);
	buffer.writeInt ((this.type == PduType.GetBulkRequest)
			? (this.options.maxRepetitions || 0)
			: 0);

	writeVarbinds (buffer, this.varbinds);

	buffer.endSequence ();
};

SimplePdu.prototype.initializeFromVariables = function (id, varbinds, options) {
	this.id = id;
	this.varbinds = varbinds;
	this.options = options || {};
	this.contextName = (options && options.context) ? options.context : "";
}

SimplePdu.prototype.initializeFromBuffer = function (reader) {
	this.type = reader.peek ();
	reader.readSequence ();

	this.id = reader.readInt ();
	this.nonRepeaters = reader.readInt ();
	this.maxRepetitions = reader.readInt ();

	this.varbinds = [];
	readVarbinds (reader, this.varbinds);
};

SimplePdu.prototype.getResponsePduForRequest = function () {
	var responsePdu = GetResponsePdu.createFromVariables(this.id, [], {});
	if ( this.contextEngineID ) {
		responsePdu.contextEngineID = this.contextEngineID;
		responsePdu.contextName = this.contextName;
	}
	return responsePdu;
};

SimplePdu.createFromVariables = function (pduClass, id, varbinds, options) {
	var pdu = new pduClass (id, varbinds, options);
	pdu.id = id;
	pdu.varbinds = varbinds;
	pdu.options = options || {};
	pdu.contextName = (options && options.context) ? options.context : "";
	return pdu;
};

var GetBulkRequestPdu = function () {
	this.type = PduType.GetBulkRequest;
	GetBulkRequestPdu.super_.apply (this, arguments);
};

util.inherits (GetBulkRequestPdu, SimplePdu);

GetBulkRequestPdu.createFromBuffer = function (reader) {
	var pdu = new GetBulkRequestPdu ();
	pdu.initializeFromBuffer (reader);
	return pdu;
};

var GetNextRequestPdu = function () {
	this.type = PduType.GetNextRequest;
	GetNextRequestPdu.super_.apply (this, arguments);
};

util.inherits (GetNextRequestPdu, SimplePdu);

GetNextRequestPdu.createFromBuffer = function (reader) {
	var pdu = new GetNextRequestPdu ();
	pdu.initializeFromBuffer (reader);
	return pdu;
};

var GetRequestPdu = function () {
	this.type = PduType.GetRequest;
	GetRequestPdu.super_.apply (this, arguments);
};

util.inherits (GetRequestPdu, SimplePdu);

GetRequestPdu.createFromBuffer = function (reader) {
	var pdu = new GetRequestPdu();
	pdu.initializeFromBuffer (reader);
	return pdu;
};

GetRequestPdu.createFromVariables = function (id, varbinds, options) {
	var pdu = new GetRequestPdu();
	pdu.initializeFromVariables (id, varbinds, options);
	return pdu;
};

var InformRequestPdu = function () {
	this.type = PduType.InformRequest;
	InformRequestPdu.super_.apply (this, arguments);
};

util.inherits (InformRequestPdu, SimplePdu);

InformRequestPdu.createFromBuffer = function (reader) {
	var pdu = new InformRequestPdu();
	pdu.initializeFromBuffer (reader);
	return pdu;
};

var SetRequestPdu = function () {
	this.type = PduType.SetRequest;
	SetRequestPdu.super_.apply (this, arguments);
};

util.inherits (SetRequestPdu, SimplePdu);

SetRequestPdu.createFromBuffer = function (reader) {
	var pdu = new SetRequestPdu ();
	pdu.initializeFromBuffer (reader);
	return pdu;
};

var TrapPdu = function () {
	this.type = PduType.Trap;
};

TrapPdu.prototype.toBuffer = function (buffer) {
	buffer.startSequence (this.type);

	buffer.writeOID (this.enterprise);
	buffer.writeBuffer (Buffer.from (this.agentAddr.split (".")),
			ObjectType.IpAddress);
	buffer.writeInt (this.generic);
	buffer.writeInt (this.specific);
	writeUint (buffer, ObjectType.TimeTicks,
			this.upTime || Math.floor (process.uptime () * 100));

	writeVarbinds (buffer, this.varbinds);

	buffer.endSequence ();
};

TrapPdu.createFromBuffer = function (reader) {
	var pdu = new TrapPdu();
	reader.readSequence ();

	pdu.enterprise = reader.readOID ();
	pdu.agentAddr = readIpAddress (reader);
	pdu.generic = reader.readInt ();
	pdu.specific = reader.readInt ();
	pdu.upTime = readUint (reader)

	pdu.varbinds = [];
	readVarbinds (reader, pdu.varbinds);

	return pdu;
};

TrapPdu.createFromVariables = function (typeOrOid, varbinds, options) {
	var pdu = new TrapPdu ();
	pdu.agentAddr = options.agentAddr || "127.0.0.1";
	pdu.upTime = options.upTime;

	if (typeof typeOrOid == "string") {
		pdu.generic = TrapType.EnterpriseSpecific;
		pdu.specific = parseInt (typeOrOid.match (/\.(\d+)$/)[1]);
		pdu.enterprise = typeOrOid.replace (/\.(\d+)$/, "");
	} else {
		pdu.generic = typeOrOid;
		pdu.specific = 0;
		pdu.enterprise = "1.3.6.1.4.1";
	}

	pdu.varbinds = varbinds;

	return pdu;
};

var TrapV2Pdu = function () {
	this.type = PduType.TrapV2;
	TrapV2Pdu.super_.apply (this, arguments);
};

util.inherits (TrapV2Pdu, SimplePdu);

TrapV2Pdu.createFromBuffer = function (reader) {
	var pdu = new TrapV2Pdu();
	pdu.initializeFromBuffer (reader);
	return pdu;
};

TrapV2Pdu.createFromVariables = function (id, varbinds, options) {
	var pdu = new TrapV2Pdu();
	pdu.initializeFromVariables (id, varbinds, options);
	return pdu;
};

var SimpleResponsePdu = function() {
};

SimpleResponsePdu.prototype.toBuffer = function (writer) {
	writer.startSequence (this.type);

	writer.writeInt (this.id);
	writer.writeInt (this.errorStatus || 0);
	writer.writeInt (this.errorIndex || 0);
	writeVarbinds (writer, this.varbinds);
	writer.endSequence ();

};

SimpleResponsePdu.prototype.initializeFromBuffer = function (reader) {
	reader.readSequence (this.type);

	this.id = reader.readInt ();
	this.errorStatus = reader.readInt ();
	this.errorIndex = reader.readInt ();

	this.varbinds = [];
	readVarbinds (reader, this.varbinds);
};

SimpleResponsePdu.prototype.initializeFromVariables = function (id, varbinds, options) {
	this.id = id;
	this.varbinds = varbinds;
	this.options = options || {};
};

var GetResponsePdu = function () {
	this.type = PduType.GetResponse;
	GetResponsePdu.super_.apply (this, arguments);
};

util.inherits (GetResponsePdu, SimpleResponsePdu);

GetResponsePdu.createFromBuffer = function (reader) {
	var pdu = new GetResponsePdu ();
	pdu.initializeFromBuffer (reader);
	return pdu;
};

GetResponsePdu.createFromVariables = function (id, varbinds, options) {
	var pdu = new GetResponsePdu();
	pdu.initializeFromVariables (id, varbinds, options);
	return pdu;
};

var ReportPdu = function () {
	this.type = PduType.Report;
	ReportPdu.super_.apply (this, arguments);
};

util.inherits (ReportPdu, SimpleResponsePdu);

ReportPdu.createFromBuffer = function (reader) {
	var pdu = new ReportPdu ();
	pdu.initializeFromBuffer (reader);
	return pdu;
};

ReportPdu.createFromVariables = function (id, varbinds, options) {
	var pdu = new ReportPdu();
	pdu.initializeFromVariables (id, varbinds, options);
	return pdu;
};

var readPdu = function (reader, scoped) {
	var pdu;
	var contextEngineID;
	var contextName;
	if ( scoped ) {
		reader.readSequence ();
		contextEngineID = reader.readString (ber.OctetString, true);
		contextName = reader.readString ();
	}
	var type = reader.peek ();

	if (type == PduType.GetResponse) {
		pdu = GetResponsePdu.createFromBuffer (reader);
	} else if (type == PduType.Report ) {
		pdu = ReportPdu.createFromBuffer (reader);
	} else if (type == PduType.Trap ) {
		pdu = TrapPdu.createFromBuffer (reader);
	} else if (type == PduType.TrapV2 ) {
		pdu = TrapV2Pdu.createFromBuffer (reader);
	} else if (type == PduType.InformRequest ) {
		pdu = InformRequestPdu.createFromBuffer (reader);
	} else if (type == PduType.GetRequest ) {
		pdu = GetRequestPdu.createFromBuffer (reader);
	} else if (type == PduType.SetRequest ) {
		pdu = SetRequestPdu.createFromBuffer (reader);
	} else if (type == PduType.GetNextRequest ) {
		pdu = GetNextRequestPdu.createFromBuffer (reader);
	} else if (type == PduType.GetBulkRequest ) {
		pdu = GetBulkRequestPdu.createFromBuffer (reader);
	} else {
		throw new ResponseInvalidError ("Unknown PDU type '" + type
				+ "' in response");
	}
	if ( scoped ) {
		pdu.contextEngineID = contextEngineID;
		pdu.contextName = contextName;
	}
	pdu.scoped = scoped;
	return pdu;
};

var createDiscoveryPdu = function (context) {
	return GetRequestPdu.createFromVariables(_generateId(), [], {context: context});
};

var Authentication = {};

Authentication.HMAC_BUFFER_SIZE = 1024*1024;
Authentication.HMAC_BLOCK_SIZE = 64;
Authentication.AUTHENTICATION_CODE_LENGTH = 12;
Authentication.AUTH_PARAMETERS_PLACEHOLDER = Buffer.from('8182838485868788898a8b8c', 'hex');

Authentication.algorithms = {};

Authentication.algorithms[AuthProtocols.md5] = {
	// KEY_LENGTH: 16,
	CRYPTO_ALGORITHM: 'md5'
};

Authentication.algorithms[AuthProtocols.sha] = {
	// KEY_LENGTH: 20,
	CRYPTO_ALGORITHM: 'sha1'
};

// Adapted from RFC3414 Appendix A.2.1. Password to Key Sample Code for MD5
Authentication.passwordToKey = function (authProtocol, authPasswordString, engineID) {
	var hashAlgorithm;
	var firstDigest;
	var finalDigest;
	var buf = Buffer.alloc (Authentication.HMAC_BUFFER_SIZE);
	var bufOffset = 0;
	var passwordIndex = 0;
	var count = 0;
	var password = Buffer.from (authPasswordString);
	var cryptoAlgorithm = Authentication.algorithms[authProtocol].CRYPTO_ALGORITHM;
	
	while (count < Authentication.HMAC_BUFFER_SIZE) {
		for (var i = 0; i < Authentication.HMAC_BLOCK_SIZE; i++) {
			buf.writeUInt8(password[passwordIndex++ % password.length], bufOffset++);
		}
		count += Authentication.HMAC_BLOCK_SIZE;
	}
	hashAlgorithm = crypto.createHash(cryptoAlgorithm);
	hashAlgorithm.update(buf);
	firstDigest = hashAlgorithm.digest();
	// debug ("First digest:  " + firstDigest.toString('hex'));

	hashAlgorithm = crypto.createHash(cryptoAlgorithm);
	hashAlgorithm.update(firstDigest);
	hashAlgorithm.update(engineID);
	hashAlgorithm.update(firstDigest);
	finalDigest = hashAlgorithm.digest();
	debug ("Localized key: " + finalDigest.toString('hex'));

	return finalDigest;
};

Authentication.addParametersToMessageBuffer = function (messageBuffer, authProtocol, authPassword, engineID) {
	var authenticationParametersOffset;
	var digestToAdd;

	// clear the authenticationParameters field in message
	authenticationParametersOffset = messageBuffer.indexOf (Authentication.AUTH_PARAMETERS_PLACEHOLDER);
	messageBuffer.fill (0, authenticationParametersOffset, authenticationParametersOffset + Authentication.AUTHENTICATION_CODE_LENGTH);

	digestToAdd = Authentication.calculateDigest (messageBuffer, authProtocol, authPassword, engineID);
	digestToAdd.copy (messageBuffer, authenticationParametersOffset, 0, Authentication.AUTHENTICATION_CODE_LENGTH);
	debug ("Added Auth Parameters: " + digestToAdd.toString('hex'));
};

Authentication.isAuthentic = function (messageBuffer, authProtocol, authPassword, engineID, digestInMessage) {
	var authenticationParametersOffset;
	var calculatedDigest;

	// clear the authenticationParameters field in message
	authenticationParametersOffset = messageBuffer.indexOf (digestInMessage);
	messageBuffer.fill (0, authenticationParametersOffset, authenticationParametersOffset + Authentication.AUTHENTICATION_CODE_LENGTH);

	calculatedDigest = Authentication.calculateDigest (messageBuffer, authProtocol, authPassword, engineID);

	// replace previously cleared authenticationParameters field in message
	digestInMessage.copy (messageBuffer, authenticationParametersOffset, 0, Authentication.AUTHENTICATION_CODE_LENGTH);

	debug ("Digest in message: " + digestInMessage.toString('hex'));
	debug ("Calculated digest: " + calculatedDigest.toString('hex'));
	return calculatedDigest.equals (digestInMessage, Authentication.AUTHENTICATION_CODE_LENGTH);
};

Authentication.calculateDigest = function (messageBuffer, authProtocol, authPassword, engineID) {
	var authKey = Authentication.passwordToKey (authProtocol, authPassword, engineID);

	// Adapted from RFC3147 Section 6.3.1. Processing an Outgoing Message
	var hashAlgorithm;
	var kIpad;
	var kOpad;
	var firstDigest;
	var finalDigest;
	var truncatedDigest;
	var i;
	var cryptoAlgorithm = Authentication.algorithms[authProtocol].CRYPTO_ALGORITHM;

	if (authKey.length > Authentication.HMAC_BLOCK_SIZE) {
		hashAlgorithm = crypto.createHash (cryptoAlgorithm);
		hashAlgorithm.update (authKey);
		authKey = hashAlgorithm.digest ();
	}

	// MD(K XOR opad, MD(K XOR ipad, msg))
	kIpad = Buffer.alloc (Authentication.HMAC_BLOCK_SIZE);
	kOpad = Buffer.alloc (Authentication.HMAC_BLOCK_SIZE);
	for (i = 0; i < authKey.length; i++) {
		kIpad[i] = authKey[i] ^ 0x36;
		kOpad[i] = authKey[i] ^ 0x5c;
	}
	kIpad.fill (0x36, authKey.length);
	kOpad.fill (0x5c, authKey.length);

	// inner MD
	hashAlgorithm = crypto.createHash (cryptoAlgorithm);
	hashAlgorithm.update (kIpad);
	hashAlgorithm.update (messageBuffer);
	firstDigest = hashAlgorithm.digest ();
	// outer MD
	hashAlgorithm = crypto.createHash (cryptoAlgorithm);
	hashAlgorithm.update (kOpad);
	hashAlgorithm.update (firstDigest);
	finalDigest = hashAlgorithm.digest ();

	truncatedDigest = Buffer.alloc (Authentication.AUTHENTICATION_CODE_LENGTH);
	finalDigest.copy (truncatedDigest, 0, 0, Authentication.AUTHENTICATION_CODE_LENGTH);
	return truncatedDigest;
};

var Encryption = {};

Encryption.PRIV_PARAMETERS_PLACEHOLDER = Buffer.from ('9192939495969798', 'hex');

Encryption.encryptPdu = function (privProtocol, scopedPdu, privPassword, authProtocol, engine) {
	var encryptFunction = Encryption.algorithms[privProtocol].encryptPdu;
	return encryptFunction (scopedPdu, privPassword, authProtocol, engine);
};

Encryption.decryptPdu = function (privProtocol, encryptedPdu, privParameters, privPassword, authProtocol, engine, forceAutoPaddingDisable) {
	var decryptFunction = Encryption.algorithms[privProtocol].decryptPdu;
	return decryptFunction (encryptedPdu, privParameters, privPassword, authProtocol, engine, forceAutoPaddingDisable);
};

Encryption.debugEncrypt = function (encryptionKey, iv, plainPdu, encryptedPdu) {
	debug ("Key: " + encryptionKey.toString ('hex'));
	debug ("IV:  " + iv.toString ('hex'));
	debug ("Plain:     " + plainPdu.toString ('hex'));
	debug ("Encrypted: " + encryptedPdu.toString ('hex'));
};

Encryption.debugDecrypt = function (decryptionKey, iv, encryptedPdu, plainPdu) {
	debug ("Key: " + decryptionKey.toString ('hex'));
	debug ("IV:  " + iv.toString ('hex'));
	debug ("Encrypted: " + encryptedPdu.toString ('hex'));
	debug ("Plain:     " + plainPdu.toString ('hex'));
};

Encryption.generateLocalizedKey = function (algorithm, authProtocol, privPassword, engineID) {
	var privLocalizedKey;
	var encryptionKey;

	privLocalizedKey = Authentication.passwordToKey (authProtocol, privPassword, engineID);
	encryptionKey = Buffer.alloc (algorithm.KEY_LENGTH);
	privLocalizedKey.copy (encryptionKey, 0, 0, algorithm.KEY_LENGTH);

	return encryptionKey;
};

Encryption.encryptPduDes = function (scopedPdu, privPassword, authProtocol, engine) {
	var des = Encryption.algorithms[PrivProtocols.des];
	var privLocalizedKey;
	var encryptionKey;
	var preIv;
	var salt;
	var iv;
	var i;
	var paddedScopedPduLength;
	var paddedScopedPdu;
	var encryptedPdu;

	encryptionKey = Encryption.generateLocalizedKey (des, authProtocol, privPassword, engine.engineID);
	privLocalizedKey = Authentication.passwordToKey (authProtocol, privPassword, engine.engineID);
	encryptionKey = Buffer.alloc (des.KEY_LENGTH);
	privLocalizedKey.copy (encryptionKey, 0, 0, des.KEY_LENGTH);
	preIv = Buffer.alloc (des.BLOCK_LENGTH);
	privLocalizedKey.copy (preIv, 0, des.KEY_LENGTH, des.KEY_LENGTH + des.BLOCK_LENGTH);

	salt = Buffer.alloc (des.BLOCK_LENGTH);
	// set local SNMP engine boots part of salt to 1, as we have no persistent engine state
	salt.fill ('00000001', 0, 4, 'hex');
	// set local integer part of salt to random
	salt.fill (crypto.randomBytes (4), 4, 8);
	iv = Buffer.alloc (des.BLOCK_LENGTH);
	for (i = 0; i < iv.length; i++) {
		iv[i] = preIv[i] ^ salt[i];
	}
	
	if (scopedPdu.length % des.BLOCK_LENGTH == 0) {
		paddedScopedPdu = scopedPdu;
	} else {
		paddedScopedPduLength = des.BLOCK_LENGTH * (Math.floor (scopedPdu.length / des.BLOCK_LENGTH) + 1);
		paddedScopedPdu = Buffer.alloc (paddedScopedPduLength);
		scopedPdu.copy (paddedScopedPdu, 0, 0, scopedPdu.length);
	}
	cipher = crypto.createCipheriv (des.CRYPTO_ALGORITHM, encryptionKey, iv);
	encryptedPdu = cipher.update (paddedScopedPdu);
	encryptedPdu = Buffer.concat ([encryptedPdu, cipher.final()]);
	// Encryption.debugEncrypt (encryptionKey, iv, paddedScopedPdu, encryptedPdu);

	return {
		encryptedPdu: encryptedPdu,
		msgPrivacyParameters: salt
	};
};

Encryption.decryptPduDes = function (encryptedPdu, privParameters, privPassword, authProtocol, engine, forceAutoPaddingDisable) {
	var des = Encryption.algorithms[PrivProtocols.des];
	var privLocalizedKey;
	var decryptionKey;
	var preIv;
	var salt;
	var iv;
	var i;
	var decryptedPdu;

	privLocalizedKey = Authentication.passwordToKey (authProtocol, privPassword, engine.engineID);
	decryptionKey = Buffer.alloc (des.KEY_LENGTH);
	privLocalizedKey.copy (decryptionKey, 0, 0, des.KEY_LENGTH);
	preIv = Buffer.alloc (des.BLOCK_LENGTH);
	privLocalizedKey.copy (preIv, 0, des.KEY_LENGTH, des.KEY_LENGTH + des.BLOCK_LENGTH);

	salt = privParameters;
	iv = Buffer.alloc (des.BLOCK_LENGTH);
	for (i = 0; i < iv.length; i++) {
		iv[i] = preIv[i] ^ salt[i];
	}
	
	decipher = crypto.createDecipheriv (des.CRYPTO_ALGORITHM, decryptionKey, iv);
	if ( forceAutoPaddingDisable ) {
		decipher.setAutoPadding(false);
	}
	decryptedPdu = decipher.update (encryptedPdu);
	// This try-catch is a workaround for a seemingly incorrect error condition
	// - where sometimes a decrypt error is thrown with decipher.final()
	// It replaces this line which should have been sufficient:
	// decryptedPdu = Buffer.concat ([decryptedPdu, decipher.final()]);
	try {
		decryptedPdu = Buffer.concat ([decryptedPdu, decipher.final()]);
	} catch (error) {
		// debug("Decrypt error: " + error);
		decipher = crypto.createDecipheriv (des.CRYPTO_ALGORITHM, decryptionKey, iv);
		decipher.setAutoPadding(false);
		decryptedPdu = decipher.update (encryptedPdu);
		decryptedPdu = Buffer.concat ([decryptedPdu, decipher.final()]);
	}
	// Encryption.debugDecrypt (decryptionKey, iv, encryptedPdu, decryptedPdu);

	return decryptedPdu;
};

Encryption.generateIvAes = function (aes, engineBoots, engineTime, salt) {
	var iv;

	// iv = engineBoots(4) | engineTime(4) | salt(8)
	iv = Buffer.alloc (aes.BLOCK_LENGTH);
	engineBootsBuffer = Buffer.alloc (4);
	engineBootsBuffer.writeUInt32BE (engineBoots);
	engineTimeBuffer = Buffer.alloc (4);
	engineTimeBuffer.writeUInt32BE (engineTime);
	engineBootsBuffer.copy (iv, 0, 0, 4);
	engineTimeBuffer.copy (iv, 4, 0, 4);
	salt.copy (iv, 8, 0, 8);

	return iv;
}

Encryption.encryptPduAes = function (scopedPdu, privPassword, authProtocol, engine) {
	var aes = Encryption.algorithms[PrivProtocols.aes];
	var encryptionKey;
	var salt;
	var iv;
	var cipher;
	var encryptedPdu;

	encryptionKey = Encryption.generateLocalizedKey (aes, authProtocol, privPassword, engine.engineID);
	salt = Buffer.alloc (8).fill (crypto.randomBytes (8), 0, 8);
	iv = Encryption.generateIvAes (aes, engine.engineBoots, engine.engineTime, salt);
	cipher = crypto.createCipheriv (aes.CRYPTO_ALGORITHM, encryptionKey, iv);
	encryptedPdu = cipher.update (scopedPdu);
	encryptedPdu = Buffer.concat ([encryptedPdu, cipher.final()]);
	// Encryption.debugEncrypt (encryptionKey, iv, scopedPdu, encryptedPdu);

	return {
		encryptedPdu: encryptedPdu,
		msgPrivacyParameters: salt
	};
};

Encryption.decryptPduAes = function (encryptedPdu, privParameters, privPassword, authProtocol, engine) {
	var aes = Encryption.algorithms[PrivProtocols.aes];
	var decryptionKey;
	var iv;
	var decipher;
	var decryptedPdu;

	decryptionKey = Encryption.generateLocalizedKey (aes, authProtocol, privPassword, engine.engineID);
	iv = Encryption.generateIvAes (aes, engine.engineBoots, engine.engineTime, privParameters);
	decipher = crypto.createDecipheriv (aes.CRYPTO_ALGORITHM, decryptionKey, iv);
	decryptedPdu = decipher.update (encryptedPdu);
	decryptedPdu = Buffer.concat ([decryptedPdu, decipher.final()]);
	// Encryption.debugDecrypt (decryptionKey, iv, encryptedPdu, decryptedPdu);

	return decryptedPdu;
};

Encryption.addParametersToMessageBuffer = function (messageBuffer, msgPrivacyParameters) {
	privacyParametersOffset = messageBuffer.indexOf (Encryption.PRIV_PARAMETERS_PLACEHOLDER);
	msgPrivacyParameters.copy (messageBuffer, privacyParametersOffset, 0, Encryption.DES_IV_LENGTH);
};

Encryption.algorithms = {};

Encryption.algorithms[PrivProtocols.des] = {
	CRYPTO_ALGORITHM: 'des-cbc',
	KEY_LENGTH: 8,
	BLOCK_LENGTH: 8,
	encryptPdu: Encryption.encryptPduDes,
	decryptPdu: Encryption.decryptPduDes
};

Encryption.algorithms[PrivProtocols.aes] = {
	CRYPTO_ALGORITHM: 'aes-128-cfb',
	KEY_LENGTH: 16,
	BLOCK_LENGTH: 16,
	encryptPdu: Encryption.encryptPduAes,
	decryptPdu: Encryption.decryptPduAes
};

/*****************************************************************************
 ** Message class definition
 **/

var Message = function () {
}

Message.prototype.getReqId = function () {
	return this.version == Version3 ? this.msgGlobalData.msgID : this.pdu.id;
};

Message.prototype.toBuffer = function () {
	if ( this.version == Version3 ) {
		return this.toBufferV3();
	} else {
		return this.toBufferCommunity();
	}
}

Message.prototype.toBufferCommunity = function () {
	if (this.buffer)
		return this.buffer;

	var writer = new ber.Writer ();

	writer.startSequence ();

	writer.writeInt (this.version);
	writer.writeString (this.community);

	this.pdu.toBuffer (writer);

	writer.endSequence ();

	this.buffer = writer.buffer;

	return this.buffer;
};

Message.prototype.toBufferV3 = function () {
	var encryptionResult;

	if (this.buffer)
		return this.buffer;

	var writer = new ber.Writer ();

	writer.startSequence ();

	writer.writeInt (this.version);

	// HeaderData
	writer.startSequence ();
	writer.writeInt (this.msgGlobalData.msgID);
	writer.writeInt (this.msgGlobalData.msgMaxSize);
	writer.writeByte (ber.OctetString);
	writer.writeByte (1);
	writer.writeByte (this.msgGlobalData.msgFlags);
	writer.writeInt (this.msgGlobalData.msgSecurityModel);
	writer.endSequence ();

	// msgSecurityParameters
	var msgSecurityParametersWriter = new ber.Writer ();
	msgSecurityParametersWriter.startSequence ();
	//msgSecurityParametersWriter.writeString (this.msgSecurityParameters.msgAuthoritativeEngineID);
	// writing a zero-length buffer fails - should fix asn1-ber for this condition
	if ( this.msgSecurityParameters.msgAuthoritativeEngineID.length == 0 ) {
		msgSecurityParametersWriter.writeString ("");
	} else {
		msgSecurityParametersWriter.writeBuffer (this.msgSecurityParameters.msgAuthoritativeEngineID, ber.OctetString);
	}
	msgSecurityParametersWriter.writeInt (this.msgSecurityParameters.msgAuthoritativeEngineBoots);
	msgSecurityParametersWriter.writeInt (this.msgSecurityParameters.msgAuthoritativeEngineTime);
	msgSecurityParametersWriter.writeString (this.msgSecurityParameters.msgUserName);

	if ( this.hasAuthentication() ) {
		msgSecurityParametersWriter.writeBuffer (Authentication.AUTH_PARAMETERS_PLACEHOLDER, ber.OctetString);
	// should never happen where msgFlags has no authentication but authentication parameters still present
	} else if ( this.msgSecurityParameters.msgAuthenticationParameters.length > 0 ) {
		msgSecurityParametersWriter.writeBuffer (this.msgSecurityParameters.msgAuthenticationParameters, ber.OctetString);
	} else {
		msgSecurityParametersWriter.writeString ("");
	}

	if ( this.hasPrivacy() ) {
		msgSecurityParametersWriter.writeBuffer (Encryption.PRIV_PARAMETERS_PLACEHOLDER, ber.OctetString);
	// should never happen where msgFlags has no privacy but privacy parameters still present
	} else if ( this.msgSecurityParameters.msgPrivacyParameters.length > 0 ) {
		msgSecurityParametersWriter.writeBuffer (this.msgSecurityParameters.msgPrivacyParameters, ber.OctetString);
	} else {
		 msgSecurityParametersWriter.writeString ("");
	}
	msgSecurityParametersWriter.endSequence ();

	writer.writeBuffer (msgSecurityParametersWriter.buffer, ber.OctetString);

	// ScopedPDU
	var scopedPduWriter = new ber.Writer ();
	scopedPduWriter.startSequence ();
	var contextEngineID = this.pdu.contextEngineID ? this.pdu.contextEngineID : this.msgSecurityParameters.msgAuthoritativeEngineID;
	if ( contextEngineID.length == 0 ) {
		scopedPduWriter.writeString ("");
	} else {
		scopedPduWriter.writeBuffer (contextEngineID, ber.OctetString);
	}
	scopedPduWriter.writeString (this.pdu.contextName);
	this.pdu.toBuffer (scopedPduWriter);
	scopedPduWriter.endSequence ();

	if ( this.hasPrivacy() ) {
		var authoritativeEngine = {
			engineID: this.msgSecurityParameters.msgAuthoritativeEngineID,
			engineBoots: this.msgSecurityParameters.msgAuthoritativeEngineBoots,
			engineTime: this.msgSecurityParameters.msgAuthoritativeEngineTime,
		};
		encryptionResult = Encryption.encryptPdu (this.user.privProtocol, scopedPduWriter.buffer,
				this.user.privKey, this.user.authProtocol, authoritativeEngine);
		writer.writeBuffer (encryptionResult.encryptedPdu, ber.OctetString);
	} else {
		writer.writeBuffer (scopedPduWriter.buffer);
	}

	writer.endSequence ();

	this.buffer = writer.buffer;

	if ( this.hasPrivacy() ) {
		Encryption.addParametersToMessageBuffer(this.buffer, encryptionResult.msgPrivacyParameters);
	}

	if ( this.hasAuthentication() ) {
		Authentication.addParametersToMessageBuffer(this.buffer, this.user.authProtocol, this.user.authKey,
			this.msgSecurityParameters.msgAuthoritativeEngineID);
	}

	return this.buffer;
};

Message.prototype.processIncomingSecurity = function (user, responseCb) {
	if ( this.hasPrivacy() ) {
		if ( ! this.decryptPdu(user, responseCb) ) {
			return false;
		}
	}

	if ( this.hasAuthentication() && ! this.isAuthenticationDisabled() ) {
		return this.checkAuthentication(user, responseCb);
	} else {
		return true;
	}
};

Message.prototype.decryptPdu = function (user, responseCb) {
	var decryptedPdu;
	var decryptedPduReader;
	try {
		var authoratitiveEngine = {
			engineID: this.msgSecurityParameters.msgAuthoritativeEngineID,
			engineBoots: this.msgSecurityParameters.msgAuthoritativeEngineBoots,
			engineTime: this.msgSecurityParameters.msgAuthoritativeEngineTime
		};
		decryptedPdu = Encryption.decryptPdu(user.privProtocol, this.encryptedPdu,
				this.msgSecurityParameters.msgPrivacyParameters, user.privKey, user.authProtocol,
				authoratitiveEngine);
		decryptedPduReader = new ber.Reader (decryptedPdu);
		this.pdu = readPdu(decryptedPduReader, true);
		return true;
	// really really occasionally the decrypt truncates a single byte
	// causing an ASN read failure in readPdu()
	// in this case, disabling auto padding decrypts the PDU correctly
	// this try-catch provides the workaround for this condition
	} catch (possibleTruncationError) {
		try {
			decryptedPdu = Encryption.decryptPdu(user.privProtocol, this.encryptedPdu,
					this.msgSecurityParameters.msgPrivacyParameters, user.privKey, user.authProtocol,
					this.msgSecurityParameters.msgAuthoritativeEngineID, true);
			decryptedPduReader = new ber.Reader (decryptedPdu);
			this.pdu = readPdu(decryptedPduReader, true);
			return true;
		} catch (error) {
			responseCb (new ResponseInvalidError ("Failed to decrypt PDU: " + error));
			return false;
		}
	}

};

Message.prototype.checkAuthentication = function (user, responseCb) {
	if ( Authentication.isAuthentic(this.buffer, user.authProtocol, user.authKey,
			this.msgSecurityParameters.msgAuthoritativeEngineID, this.msgSecurityParameters.msgAuthenticationParameters) ) {
		return true;
	} else {
		responseCb (new ResponseInvalidError ("Authentication digest "
				+ this.msgSecurityParameters.msgAuthenticationParameters.toString ('hex')
				+ " received in message does not match digest "
				+ Authentication.calculateDigest (buffer, user.authProtocol, user.authKey,
					this.msgSecurityParameters.msgAuthoritativeEngineID).toString ('hex')
				+ " calculated for message") );
		return false;
	}

};

Message.prototype.setMsgFlags = function (bitPosition, flag) {
	if ( this.msgGlobalData && this.msgGlobalData !== undefined && this.msgGlobalData !== null ) {
		if ( flag ) {
			this.msgGlobalData.msgFlags = this.msgGlobalData.msgFlags | ( 2 ** bitPosition );
		} else {
			this.msgGlobalData.msgFlags = this.msgGlobalData.msgFlags & ( 255 - 2 ** bitPosition );
		}
	}
}

Message.prototype.hasAuthentication = function () {
	return this.msgGlobalData && this.msgGlobalData.msgFlags && this.msgGlobalData.msgFlags & 1;
};

Message.prototype.setAuthentication = function (flag) {
	this.setMsgFlags (0, flag);
};

Message.prototype.hasPrivacy = function () {
	return this.msgGlobalData && this.msgGlobalData.msgFlags && this.msgGlobalData.msgFlags & 2;
};

Message.prototype.setPrivacy = function (flag) {
	this.setMsgFlags (1, flag);
};

Message.prototype.isReportable = function () {
	return this.msgGlobalData && this.msgGlobalData.msgFlags && this.msgGlobalData.msgFlags & 4;
};

Message.prototype.setReportable = function (flag) {
	this.setMsgFlags (2, flag);
};

Message.prototype.isAuthenticationDisabled = function () {
	return this.disableAuthentication;
};

Message.prototype.hasAuthoritativeEngineID = function () {
	return this.msgSecurityParameters && this.msgSecurityParameters.msgAuthoritativeEngineID &&
		this.msgSecurityParameters.msgAuthoritativeEngineID != "";
};

Message.prototype.createReportResponseMessage = function (engine, context) {
	var user = {
		name: "",
		level: SecurityLevel.noAuthNoPriv
	};
	var responseSecurityParameters = {
		msgAuthoritativeEngineID: engine.engineID,
		msgAuthoritativeEngineBoots: engine.engineBoots,
		msgAuthoritativeEngineTime: engine.engineTime,
		msgUserName: user.name,
		msgAuthenticationParameters: "",
		msgPrivacyParameters: ""
	};
	var reportPdu = ReportPdu.createFromVariables (this.pdu.id, [], {});
	reportPdu.contextName = context;
	var responseMessage = Message.createRequestV3 (user, responseSecurityParameters, reportPdu);
	responseMessage.msgGlobalData.msgID = this.msgGlobalData.msgID;
	return responseMessage;
};

Message.prototype.createResponseForRequest = function (responsePdu) {
	if ( this.version == Version3 ) {
		return this.createV3ResponseFromRequest(responsePdu);
	} else {
		return this.createCommunityResponseFromRequest(responsePdu);
	}
};

Message.prototype.createCommunityResponseFromRequest = function (responsePdu) {
	return Message.createCommunity(this.version, this.community, responsePdu);
};

Message.prototype.createV3ResponseFromRequest = function (responsePdu) {
	var responseUser = {
		name: this.user.name,
		level: this.user.name,
		authProtocol: this.user.authProtocol,
		authKey: this.user.authKey,
		privProtocol: this.user.privProtocol,
		privKey: this.user.privKey
	};
	var responseSecurityParameters = {
		msgAuthoritativeEngineID: this.msgSecurityParameters.msgAuthoritativeEngineID,
		msgAuthoritativeEngineBoots: this.msgSecurityParameters.msgAuthoritativeEngineBoots,
		msgAuthoritativeEngineTime: this.msgSecurityParameters.msgAuthoritativeEngineTime,
		msgUserName: this.msgSecurityParameters.msgUserName,
		msgAuthenticationParameters: "",
		msgPrivacyParameters: ""
	};
	var responseGlobalData = {
		msgID: this.msgGlobalData.msgID,
		msgMaxSize: 65507,
		msgFlags: this.msgGlobalData.msgFlags & (255 - 4),
		msgSecurityModel: 3
	};
	return Message.createV3 (responseUser, responseGlobalData, responseSecurityParameters, responsePdu);
};

Message.createCommunity = function (version, community, pdu) {
	var message = new Message ();

	message.version = version;
	message.community = community;
	message.pdu = pdu;

	return message;
};

Message.createRequestV3 = function (user, msgSecurityParameters, pdu) {
	var authFlag = user.level == SecurityLevel.authNoPriv || user.level == SecurityLevel.authPriv ? 1 : 0;
	var privFlag = user.level == SecurityLevel.authPriv ? 1 : 0;
	var reportableFlag = ( pdu.type == PduType.GetResponse || pdu.type == PduType.TrapV2 ) ? 0 : 1;
	var msgGlobalData = {
		msgID: _generateId(), // random ID
		msgMaxSize: 65507,
		msgFlags: reportableFlag * 4 | privFlag * 2 | authFlag * 1,
		msgSecurityModel: 3
	};
	return Message.createV3 (user, msgGlobalData, msgSecurityParameters, pdu);
};

Message.createV3 = function (user, msgGlobalData, msgSecurityParameters, pdu) {
	var message = new Message ();

	message.version = 3;
	message.user = user;
	message.msgGlobalData = msgGlobalData;
	message.msgSecurityParameters = {
		msgAuthoritativeEngineID: msgSecurityParameters.msgAuthoritativeEngineID || Buffer.from(""),
		msgAuthoritativeEngineBoots: msgSecurityParameters.msgAuthoritativeEngineBoots || 0,
		msgAuthoritativeEngineTime: msgSecurityParameters.msgAuthoritativeEngineTime || 0,
		msgUserName: user.name || "",
		msgAuthenticationParameters: "",
		msgPrivacyParameters: ""
	};
	message.pdu = pdu;

	return message;
};

Message.createDiscoveryV3 = function (pdu) {
	var msgSecurityParameters = {
		msgAuthoritativeEngineID: Buffer.from(""),
		msgAuthoritativeEngineBoots: 0,
		msgAuthoritativeEngineTime: 0
	};
	var emptyUser = {
		name: "",
		level: SecurityLevel.noAuthNoPriv
	};
	return Message.createRequestV3 (emptyUser, msgSecurityParameters, pdu);
}

Message.createFromBuffer = function (buffer, user) {
	var reader = new ber.Reader (buffer);
	var message = new Message();

	reader.readSequence ();

	message.version = reader.readInt ();

	if (message.version != 3) {
		message.community = reader.readString ();
		message.pdu = readPdu(reader, false);
	} else {
		// HeaderData
		message.msgGlobalData = {};
		reader.readSequence ();
		message.msgGlobalData.msgID = reader.readInt ();
		message.msgGlobalData.msgMaxSize = reader.readInt ();
		message.msgGlobalData.msgFlags = reader.readString (ber.OctetString, true)[0];
		message.msgGlobalData.msgSecurityModel = reader.readInt ();

		// msgSecurityParameters
		message.msgSecurityParameters = {};
		var msgSecurityParametersReader = new ber.Reader (reader.readString (ber.OctetString, true));
		msgSecurityParametersReader.readSequence ();
		message.msgSecurityParameters.msgAuthoritativeEngineID = msgSecurityParametersReader.readString (ber.OctetString, true);
		message.msgSecurityParameters.msgAuthoritativeEngineBoots = msgSecurityParametersReader.readInt ();
		message.msgSecurityParameters.msgAuthoritativeEngineTime = msgSecurityParametersReader.readInt ();
		message.msgSecurityParameters.msgUserName = msgSecurityParametersReader.readString ();
		message.msgSecurityParameters.msgAuthenticationParameters = Buffer.from(msgSecurityParametersReader.readString (ber.OctetString, true));
		message.msgSecurityParameters.msgPrivacyParameters = Buffer.from(msgSecurityParametersReader.readString (ber.OctetString, true));

		if ( message.hasPrivacy() ) {
			message.encryptedPdu = reader.readString (ber.OctetString, true);
			message.pdu = null;
		} else {
			message.pdu = readPdu(reader, true);
		}
	}

	message.buffer = buffer;

	return message;
};


var Req = function (session, message, feedCb, responseCb, options) {

	this.message = message;
	this.responseCb = responseCb;
	this.retries = session.retries;
	this.timeout = session.timeout;
	// Add timeout backoff
	this.backoff = session.backoff;
	this.onResponse = session.onSimpleGetResponse;
	this.feedCb = feedCb;
	this.port = (options && options.port) ? options.port : session.port;
	this.context = session.context;
};

Req.prototype.getId = function() {
	return this.message.getReqId ();
};


/*****************************************************************************
 ** Session class definition
 **/

var Session = function (target, authenticator, options) {
	this.target = target || "127.0.0.1";

	options = options || {};
	this.version = options.version
			? options.version
			: Version1;

	if ( this.version == Version3 ) {
		this.user = authenticator;
	} else {
		this.community = authenticator || "public";
	}

	this.transport = options.transport
			? options.transport
			: "udp4";
	this.port = options.port
			? options.port
			: 161;
	this.trapPort = options.trapPort
			? options.trapPort
			: 162;

	this.retries = (options.retries || options.retries == 0)
			? options.retries
			: 1;
	this.timeout = options.timeout
			? options.timeout
			: 5000;

	this.backoff = options.backoff >= 1.0
			? options.backoff
			: 1.0;

	this.sourceAddress = options.sourceAddress
			? options.sourceAddress
			: undefined;
	this.sourcePort = options.sourcePort
			? parseInt(options.sourcePort)
			: undefined;

	this.idBitsSize = options.idBitsSize
			? parseInt(options.idBitsSize)
			: 32;

	this.context = options.context
			? options.context
			: "";

	this.backwardsGetNexts = (typeof options.backwardsGetNexts !== 'undefined')
			? options.backwardsGetNexts
			: true;

	DEBUG = options.debug;

	this.engine = new Engine ();
	this.reqs = {};
	this.reqCount = 0;

	this.dgram = dgram.createSocket (this.transport);
	this.dgram.unref();
	
	var me = this;
	this.dgram.on ("message", me.onMsg.bind (me));
	this.dgram.on ("close", me.onClose.bind (me));
	this.dgram.on ("error", me.onError.bind (me));

	if (this.sourceAddress || this.sourcePort)
		this.dgram.bind (this.sourcePort, this.sourceAddress);
};

util.inherits (Session, events.EventEmitter);

Session.prototype.close = function () {
	this.dgram.close ();
	return this;
};

Session.prototype.cancelRequests = function (error) {
	var id;
	for (id in this.reqs) {
		var req = this.reqs[id];
		this.unregisterRequest (req.getId ());
		req.responseCb (error);
	}
};

function _generateId (bitSize) {
	if (bitSize === 16) {
		return Math.floor(Math.random() * 10000) % 65535;
	}
	return Math.floor(Math.random() * 1