| static private ParseHeader ( byte mb, int &offset, int &length ) : byte | ||
| mb | byte | BER encoded data |
| offset | int | Offset in the packet to start parsing the header from |
| length | int | Length of the data in the section starting with parsed header |
| return | byte | |
/// <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>
/// <exception cref="SnmpInvalidVersionException">Thrown when attempting to parse an SNMP packet that is not version 3</exception>
/// <exception cref="OverflowException">Thrown when header specifies packet length that is longer then the amount of data received.</exception>
/// <exception cref="SnmpDecodingException">Thrown when invalid sequence is enountered while decoding global message data sequence</exception>
/// <exception cref="SnmpException">Thrown with SnmpException.UnsupportedNoAuthPriv when packet is using privacy without authentication (not allowed)</exception>
/// <exception cref="SnmpException">Thrown with SnmpException.UnsupportedSecurityModel when packet is sent with security model other then USM (only USM is defined in SNMPv3 standard)</exception>
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
byte asnType = AsnType.ParseHeader(buffer, ref offset, out int len);
if (asnType != SnmpConstants.SMI_SEQUENCE)
{
throw new SnmpDecodingException("Invalid sequence type when decoding 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 != USM.Type)
{
throw new SnmpException(SnmpException.UnsupportedSecurityModel,
"Class only support SNMP Version 3 User Security Model.");
}
// parse user security model
offset = USM.Decode(buffer, offset);
return(USM);
}
/// <summary>
/// Decode received SNMP packet.
/// </summary>
/// <param name="buffer">BER encoded packet buffer</param>
/// <param name="length">BER encoded packet buffer length</param>
/// <exception cref="SnmpException">Thrown when invalid encoding has been found in the packet</exception>
/// <exception cref="OverflowException">Thrown when parsed header points to more data then is available in the packet</exception>
/// <exception cref="SnmpInvalidVersionException">Thrown when parsed packet is not SNMP version 1</exception>
/// <exception cref="SnmpInvalidPduTypeException">Thrown when received PDU is of a type not supported by SNMP version 1</exception>
public override int Decode(byte[] buffer, int length)
{
MutableByte buf = new MutableByte(buffer, length);
int offset = 0;
offset = base.Decode(buffer, buffer.Length);
if (Version != SnmpVersion.Ver2)
{
throw new SnmpInvalidVersionException("Invalid protocol version");
}
offset = _snmpCommunity.Decode(buf, offset);
int tmpOffset = offset;
byte asnType = AsnType.ParseHeader(buf, ref tmpOffset, out int headerLength);
// Check packet length
if (headerLength + offset > buf.Length)
{
throw new OverflowException("Insufficient data in packet");
}
if (asnType != (byte)PduType.Get && asnType != (byte)PduType.GetNext && asnType != (byte)PduType.Set &&
asnType != (byte)PduType.GetBulk && asnType != (byte)PduType.Response && asnType != (byte)PduType.V2Trap &&
asnType != (byte)PduType.Inform)
{
throw new SnmpInvalidPduTypeException("Invalid SNMP operation received: " + string.Format("0x{0:x2}", asnType));
}
// Now process the Protocol Data Unit
offset = Pdu.Decode(buf, offset);
return(length);
}
/// <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>
/// 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>
/// 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 ESnmpVersion GetProtocolVersion(byte[] buffer, int bufferLength)
{
int offset = 0;
byte asnType = AsnType.ParseHeader(buffer, ref offset, out int length);
if ((offset + length) > bufferLength)
{
throw new SnmpDecodingException("Cannot parse SNMP version from packet, input past end");
}
if (asnType != SnmpConstants.SmiSequence)
{
throw new SnmpDecodingException("Invalid sequence type at the start of the SNMP packet.");
}
Integer32 version = new Integer32();
offset = version.Decode(buffer, offset);
return((ESnmpVersion)version.Value);
}
/// <summary>
/// Decode received packet. This method overrides the base implementation that cannot be used with this type of the packet.
/// </summary>
/// <param name="buffer">Packet buffer</param>
/// <param name="length">Buffer length</param>
public override int decode(byte[] buffer, int length)
{
int offset = 0;
MutableByte buf = new MutableByte(buffer, length);
offset = base.decode(buffer, length);
// parse community
offset = _snmpCommunity.decode(buf, offset);
// look ahead to make sure this is a TRAP packet
int tmpOffset = offset;
byte tmpAsnType = AsnType.ParseHeader(buffer, ref tmpOffset, out _);
if (tmpAsnType != (byte)PduType.Trap)
{
throw new SnmpException(string.Format("Invalid SNMP ASN.1 type. Received: {0:x2}", tmpAsnType));
}
// decode protocol data unit
offset = this.Pdu.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>
/// <returns>The length of the decoded segment</returns>
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)ESnmpVersion.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.SmiSequence)
{
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 = messageFlags.Decode(buffer, offset);
// verify that a valid authentication/privacy configuration is present in the packet
if (messageFlags.Authentication == false && messageFlags.Privacy == true)
{
throw new SnmpException(SnmpException.EErrorCode.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.EErrorCode.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 (messageFlags.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 (messageFlags.Privacy && userSecurityModel.EngineId.Length > 0)
{
IPrivacyProtocol privacyProtocol = PrivacyProtocol.GetInstance(userSecurityModel.Privacy);
if (privacyProtocol == null)
{
throw new SnmpException(SnmpException.EErrorCode.UnsupportedPrivacyProtocol, "Privacy protocol requested is not supported.");
}
if (userSecurityModel.PrivacyParameters.Length != privacyProtocol.PrivacyParametersLength)
{
throw new SnmpException(SnmpException.EErrorCode.InvalidPrivacyParameterLength, "Invalid privacy parameters field length.");
}
// Initialize a temporary OctetString class to hold encrypted ScopedPdu
OctetString encryptedScopedPdu = new OctetString();
offset = 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);
}
/// <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>
public override int decode(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);
// 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(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.");
}
// build privacy key
IAuthenticationDigest auth = Authentication.GetInstance(_userSecurityModel.Authentication);
if (auth == null)
{
throw new SnmpException(SnmpException.UnsupportedNoAuthPriv, "Invalid authentication protocol.");
}
byte[] pkey = auth.PasswordToKey(_userSecurityModel.PrivacySecret, _userSecurityModel.EngineId);
// extend key if it is too short
if (pkey.Length < privacyProtocol.MinimumKeyLength)
{
pkey = privacyProtocol.ExtendShortKey(pkey, new OctetString(_userSecurityModel.PrivacySecret), _userSecurityModel.EngineId, auth);
}
// Initialize a temporary OctetString class to hold encrypted ScopedPdu
OctetString encryptedScopedPdu = new OctetString();
offset = encryptedScopedPdu.decode(buffer, offset);
// decode encrypted packet
byte[] decryptedScopedPdu = privacyProtocol.Decrypt(encryptedScopedPdu, 0, encryptedScopedPdu.Length, pkey, _userSecurityModel.EngineBoots, _userSecurityModel.EngineTime, _userSecurityModel.PrivacyParameters);
int tempOffset = 0;
offset = _scopedPdu.decode(decryptedScopedPdu, tempOffset);
}
else
{
offset = _scopedPdu.decode(buffer, offset);
}
return(offset);
}
