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);
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 != _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;
}
