/// <summary>
/// "Look-ahead" decode of SNMP packet header including USM information
/// </summary>
/// <remarks>
/// Decode first component of the SNMP version 3 packet allowing the caller to retrieve USM SecureName needed to retrieve
/// client security parameters that will allow authentication and privacy decryption to take place.
///
/// This method is used to support Agent like behavior or to handle unsolicited packets like TRAP and INFORMs. In all of
/// these cases, sender of packets will forward a packet without a request being sent by you. In turn, you will need
/// to parse enough of the packet to retrieve SecureName which you can use to retrieve security parameters associated with
/// that user and attempt to authorize and privacy decrypt the received packet.
///
/// Only use this method when your application is acting as an Agent or if you need to process TRAP and INFORM packets.
/// </remarks>
/// <param name="berBuffer">Raw SNMP version 3 packet</param>
/// <param name="length">SNMP version 3 packet length</param>
/// <returns>UserSecurityModel class parsed from the parameter SNMP version 3 packet</returns>
public UserSecurityModel GetUSM(byte[] berBuffer, int length)
{
MutableByte buffer = new MutableByte(berBuffer, length);
int offset = 0;
// let base class parse first sequence and SNMP version number
offset = base.decode(buffer, length);
// check for correct SNMP protocol version
if (_protocolVersion != (int)SnmpVersion.Ver3)
{
throw new SnmpInvalidVersionException("Expecting SNMP version 3.");
}
// now grab the global message data sequence header information
int len = 0;
byte asnType = AsnType.ParseHeader(buffer, ref offset, out len);
// check that packet size can accommodate the length specified in the header
if (len > (buffer.Length - offset))
{
throw new OverflowException("Packet is too small to contain the data described in the header.");
}
// retrieve message id
offset = _messageId.decode(buffer, offset);
// max message size
offset = _maxMessageSize.decode(buffer, offset);
// message flags
offset = _msgFlags.decode(buffer, offset);
// verify that a valid authentication/privacy configuration is present in the packet
if (_msgFlags.Authentication == false && _msgFlags.Privacy == true)
{
throw new SnmpException(SnmpException.UnsupportedNoAuthPriv,
"SNMP version 3 noAuthPriv security combination is not supported.");
}
// security model code
offset = _securityModel.decode(buffer, offset);
// we only support USM. code = 0x03
if (_securityModel.Value != _userSecurityModel.Type)
{
throw new SnmpException(SnmpException.UnsupportedSecurityModel,
"Class only support SNMP Version 3 User Security Model.");
}
// parse user security model
offset = _userSecurityModel.decode(buffer, offset);
return(_userSecurityModel);
}
/// <summary>Decode BER encoded SNMP version 1 trap packet</summary>
/// <param name="buffer">BER encoded buffer</param>
/// <param name="offset">Offset in the packet to start decoding from</param>
/// <returns>Buffer position after the decoded value.</returns>
/// <exception cref="SnmpException">Invalid SNMP Pdu type received. Not an SNMP version 1 Trap PDU.</exception>
/// <exception cref="SnmpException">Invalid Variable Binding list encoding.</exception>
public override int decode(byte[] buffer, int offset)
{
int headerLength;
byte asnType = ParseHeader(buffer, ref offset, out headerLength);
if (asnType != (byte)PduType.Trap)
{
throw new SnmpException("Invalid PDU type.");
}
if (headerLength > buffer.Length - offset)
{
throw new OverflowException("Packet is too short.");
}
offset = _enterprise.decode(buffer, offset);
offset = _agentAddr.decode(buffer, offset);
offset = _generic.decode(buffer, offset);
offset = _specific.decode(buffer, offset);
offset = _timeStamp.decode(buffer, offset);
// clean out the current variables
_variables.Clear();
offset = _variables.decode(buffer, offset);
return(offset);
}
/// <summary>
/// Decode USM portion of the SNMP version 3 packet.
/// </summary>
/// <param name="buffer">Received SNMP packet BER encoded</param>
/// <param name="offset">Offset within the buffer to start decoding USM information</param>
/// <returns>Buffer position after the decoded value</returns>
/// <exception cref="SnmpDecodingException">Thrown when decoding enountered invalid data type in USM information</exception>
/// <exception cref="OverflowException">Thrown when packet is too small to contain information length specified in header</exception>
public override int decode(byte[] buffer, int offset)
{
// Grab the octet string header
int len;
byte type = ParseHeader(buffer, ref offset, out len);
if (type != OCTETSTRING)
{
throw new SnmpDecodingException("Invalid value type found while looking for USM header.");
}
if (len > (buffer.Length - offset))
{
throw new OverflowException("Packet too small");
}
// Now grab the sequence header
type = ParseHeader(buffer, ref offset, out len);
if (type != SnmpConstants.SMI_SEQUENCE)
{
throw new SnmpDecodingException("Sequence missing from USM header.");
}
if (len > (buffer.Length - offset))
{
throw new OverflowException("Packet too small");
}
// now grab values one at the time
offset = _engineId.decode(buffer, offset);
offset = _engineBoots.decode(buffer, offset);
offset = _engineTime.decode(buffer, offset);
offset = _securityName.decode(buffer, offset);
int saveOffset = offset;
offset = _authenticationParameters.decode(buffer, offset);
if (_authenticationParameters.Length > 0)
{
// walk through and set the authentication parameters to 0x00 in the packet
saveOffset += 2; // Skip BER encoded variable type and length
for (int i = 0; i < _authenticationParameters.Length; i++)
{
buffer[saveOffset + i] = 0x00;
}
}
offset = _privacyParameters.decode(buffer, offset);
return(offset);
}
/// <summary>
/// Decode BER encoded Pdu
/// </summary>
/// <remarks>
/// Decodes the protocol data unit from the passed buffer. If an error
/// occurs during the decoding sequence then an AsnDecodingException is
/// thrown by the method. The value is decoded using the AsnEncoder
/// passed to the object.
/// </remarks>
/// <param name="buffer">BER encoded buffer</param>
/// <param name="offset">The offset byte to begin decoding</param>
/// <returns>Buffer position after the decoded value</returns>
/// <exception cref="OverflowException">Thrown when header points to more data then is available.</exception>
public override int decode(byte[] buffer, int offset)
{
int headerLength;
byte asnType = ParseHeader(buffer, ref offset, out headerLength);
if (offset + headerLength > buffer.Length)
{
throw new OverflowException("Insufficient data in packet");
}
_asnType = asnType;
// request id
offset = _requestId.decode(buffer, offset);
// error status
offset = _errorStatus.decode(buffer, offset);
// error index
offset = _errorIndex.decode(buffer, offset);
// clean out the current variables
_vbs.Clear();
// decode the Variable binding collection
offset = _vbs.decode(buffer, offset);
// if Pdu is an SNMP version 2 TRAP, remove sysUpTime and trapObjectID from the VarBinds array
if (Type == PduType.V2Trap || Type == PduType.Inform)
{
if (_vbs.Count > 0)
{
if (_vbs[0].Oid.Equals(SnmpConstants.SysUpTime))
{
_trapTimeStamp.Set(_vbs[0].Value);
_vbs.RemoveAt(0); // remove sysUpTime
}
}
if (_vbs.Count > 0)
{
if (_vbs[0].Oid.Equals(SnmpConstants.TrapObjectId))
{
_trapObjectID.Set((Oid)_vbs[0].Value);
_vbs.RemoveAt(0); // remove sysUpTime
}
}
}
return(offset);
}
/// <summary>
/// Get SNMP protocol version from the packet. This routine does not verify if version number is valid. Caller
/// should verify that returned value represents a valid SNMP protocol version number.
///
/// <code>
/// int protocolVersion = Packet.GetProtocolVersion(inPacket, inLength);
/// if( protocolVersion != -1 )
/// {
/// if( protocolVersion == SnmpConstants.SNMPV1 || protocolVersion == SnmpConstants.SNMPV2 || protocolVersion == SnmpConstants.SNMPV3 )
/// {
/// // do something
/// }
/// else
/// {
/// Console.WriteLine("Invalid SNMP protocol version.");
/// }
/// }
/// else
/// {
/// Console.WriteLine("Invalid SNMP packet.");
/// }
/// </code>
/// </summary>
/// <param name="buffer">BER encoded SNMP packet</param>
/// <param name="bufferLength">Length of the BER encoded packet</param>
/// <returns>Returns SNMP protocol version, if packet is not valid returned value is -1.</returns>
public static int GetProtocolVersion(byte[] buffer, int bufferLength)
{
int offset = 0;
int length = 0;
byte asnType = AsnType.ParseHeader(buffer, ref offset, out length);
if ((offset + length) > bufferLength)
{
return(-1); // This is not a valid packet
}
Integer32 version = new Integer32();
offset = version.decode(buffer, offset);
return(version.Value);
}
/// <summary>
/// Decode SNMP packet header. This class decodes the initial sequence and SNMP protocol version
/// number.
/// </summary>
/// <param name="buffer">BER encoded SNMP packet</param>
/// <param name="length">Packet length</param>
/// <returns>Offset position after the initial sequence header and protocol version value</returns>
public virtual int decode(byte[] buffer, int length)
{
int offset = 0;
if (length < 2)
{
// we need at least 2 bytes
throw new OverflowException("Packet too small.");
}
// make sure you get the right length buffer to be able to check for over/under flow errors
MutableByte buf = new MutableByte(buffer, length);
Sequence seq = new Sequence();
offset = seq.decode(buf, offset);
offset = _protocolVersion.decode(buf, offset);
return(offset);
}
/// <summary>
/// Get SNMP protocol version from the packet. This routine does not verify if version number is valid. Caller
/// should verify that returned value represents a valid SNMP protocol version number.
///
/// <code>
/// int protocolVersion = Packet.GetProtocolVersion(inPacket, inLength);
/// if( protocolVersion != -1 )
/// {
/// if( protocolVersion == SnmpConstants.SNMPV1 || protocolVersion == SnmpConstants.SNMPV2 || protocolVersion == SnmpConstants.SNMPV3 )
/// {
/// // do something
/// }
/// else
/// {
/// Console.WriteLine("Invalid SNMP protocol version.");
/// }
/// }
/// else
/// {
/// Console.WriteLine("Invalid SNMP packet.");
/// }
/// </code>
/// </summary>
/// <param name="buffer">BER encoded SNMP packet</param>
/// <param name="bufferLength">Length of the BER encoded packet</param>
/// <returns>Returns SNMP protocol version, if packet is not valid returned value is -1.</returns>
/// <exception cref="SnmpDecodingException">Thrown when invalid sequence type is found at the start of the SNMP packet being decoded</exception>
public static int GetProtocolVersion(byte[] buffer, int bufferLength)
{
int offset = 0;
byte asnType = AsnType.ParseHeader(buffer, ref offset, out int length);
if ((offset + length) > bufferLength)
{
return(-1); // This is not a valid packet
}
if (asnType != SnmpConstants.SMI_SEQUENCE)
{
throw new SnmpDecodingException("Invalid sequence type at the start of the SNMP packet.");
}
Integer32 version = new Integer32();
_ = version.decode(buffer, offset);
return(version.Value);
}
/// <summary>
/// Decode SNMP packet header. This class decodes the initial sequence and SNMP protocol version
/// number.
/// </summary>
/// <param name="buffer">BER encoded SNMP packet</param>
/// <param name="length">Packet length</param>
/// <returns>Offset position after the initial sequence header and protocol version value</returns>
/// <exception cref="SnmpDecodingException">
/// Thrown when invalid sequence type is found at the start of the SNMP packet
/// being decoded
/// </exception>
public virtual int decode(byte[] buffer, int length)
{
var offset = 0;
if (length < 2)
{
throw new OverflowException("Packet too small.");
}
// make sure you get the right length buffer to be able to check for over/under flow errors
var buf = new MutableByte(buffer, length);
var seq = new Sequence();
offset = seq.decode(buf, offset);
if (seq.Type != SnmpConstants.SMI_SEQUENCE)
{
throw new SnmpDecodingException("Invalid sequence type at the start of the SNMP packet.");
}
offset = _protocolVersion.decode(buf, offset);
return(offset);
}
/// <summary>
/// Decode SNMP version 3 packet. This method will perform authentication check and decode privacy protected <see cref="ScopedPdu"/>. This method will
/// not check for the timeliness of the packet, correct engine boot value or engine id because it does not have a reference to the engine time prior to this call.
/// </summary>
/// <param name="berBuffer">BER encoded SNMP version 3 packet buffer</param>
/// <param name="length">Buffer length</param>
/// <param name="authKey">Authentication key (not password)</param>
/// <param name="privKey">Privacy key (not password)</param>
public int decode(byte[] berBuffer, int length, byte[] authKey, byte[] privKey)
{
MutableByte buffer = new MutableByte(berBuffer, length);
int offset = 0;
// let base class parse first sequence and SNMP version number
offset = base.decode(buffer, length);
// check for correct SNMP protocol version
if (_protocolVersion != (int)SnmpVersion.Ver3)
throw new SnmpInvalidVersionException("Expecting SNMP version 3.");
// now grab the global message data sequence header information
byte asnType = AsnType.ParseHeader(buffer, ref offset, out int len);
if (asnType != SnmpConstants.SMI_SEQUENCE)
throw new SnmpDecodingException("Invalid sequence type in global message data sequence.");
// check that packet size can accommodate the length specified in the header
if (len > (buffer.Length - offset))
throw new OverflowException("Packet is too small to contain the data described in the header.");
// retrieve message id
offset = _messageId.decode(buffer, offset);
// max message size
offset = _maxMessageSize.decode(buffer, offset);
// message flags
offset = _msgFlags.decode(buffer, offset);
// verify that a valid authentication/privacy configuration is present in the packet
if (_msgFlags.Authentication == false && _msgFlags.Privacy == true)
throw new SnmpException(SnmpException.UnsupportedNoAuthPriv, "SNMP version 3 noAuthPriv security combination is not supported.");
// security model code
offset = _securityModel.decode(buffer, offset);
// we only support USM. code = 0x03
if (_securityModel.Value != _userSecurityModel.Type)
throw new SnmpException(SnmpException.UnsupportedSecurityModel, "Class only support SNMP Version 3 User Security Model.");
// parse user security model
offset = _userSecurityModel.decode(buffer, offset);
// Authenticate message if authentication flag is set and packet is not a discovery packet
if (_msgFlags.Authentication && _userSecurityModel.EngineId.Length > 0)
{
// Authenticate packet
if (_userSecurityModel.AuthenticationParameters.Length != 12)
throw new SnmpAuthenticationException("Invalid authentication parameter field length.");
if (!_userSecurityModel.IsAuthentic(authKey, buffer))
throw new SnmpAuthenticationException("Authentication of the incoming packet failed.");
}
// Decode ScopedPdu if it is privacy protected and packet is not a discovery packet
if (_msgFlags.Privacy && _userSecurityModel.EngineId.Length > 0)
{
IPrivacyProtocol privacyProtocol = PrivacyProtocol.GetInstance(_userSecurityModel.Privacy);
if (privacyProtocol == null)
{
throw new SnmpException(SnmpException.UnsupportedPrivacyProtocol, "Privacy protocol requested is not supported.");
}
if (_userSecurityModel.PrivacyParameters.Length != privacyProtocol.PrivacyParametersLength)
throw new SnmpException(SnmpException.InvalidPrivacyParameterLength, "Invalid privacy parameters field length.");
// Initialize a temporary OctetString class to hold encrypted ScopedPdu
OctetString encryptedScopedPdu = new OctetString();
_ = encryptedScopedPdu.decode(buffer, offset);
// decode encrypted packet
byte[] decryptedScopedPdu = privacyProtocol.Decrypt(encryptedScopedPdu, 0, encryptedScopedPdu.Length, privKey, _userSecurityModel.EngineBoots, _userSecurityModel.EngineTime, _userSecurityModel.PrivacyParameters);
int tempOffset = 0;
offset = _scopedPdu.decode(decryptedScopedPdu, tempOffset);
}
else
offset = _scopedPdu.decode(buffer, offset);
return offset;
}