| public decode ( byte buffer, int offset ) : int | ||
| buffer | byte | BER encoded buffer |
| offset | int | Offset within the buffer to start decoding process |
| return | int | |
/// <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 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;
}