/// <summary>
/// Decode BER encoded <see cref="ScopedPdu"/> values. This method does not perform SNMP v3 privacy operations
/// and is not aware of privacy requirements.
///
/// To decode a privacy protected SNMP v3 packet, you will need to a) extract <see cref="OctetString"/> value
/// holding encrypted <see cref="ScopedPdu"/> data, b) decrypt the encrypted ScopedPdu data into an unecrypted
/// byte array, c) pass unencrypted <see cref="ScopedPdu"/> and BER encoded byte array to this method for
/// final data conversion from BER into individual sequences and variables.
/// </summary>
/// <param name="buffer">Buffer holding BER encoded <see cref="ScopedPdu"/> data</param>
/// <param name="offset">Offset within the buffer BER encoded <see cref="ScopedPdu"/> data begins.</param>
/// <returns>Offset position after parsed ScopedPdu</returns>
/// <exception cref="SnmpDecodingException">Error was encountered when decoding the PDU</exception>
/// <exception cref="OverflowException">Thrown when buffer is too short to contain the PDU</exception>
public override int decode(byte[] buffer, int offset)
{
int length;
byte sequenceType = ParseHeader(buffer, ref offset, out length);
if (sequenceType != SnmpConstants.SMI_SEQUENCE)
{
throw new SnmpDecodingException("Invalid ScopedPdu sequence detected. Invalid ScopedPdu encoding.");
}
// verify packet can match parsed length
if (length > (buffer.Length - offset))
{
throw new OverflowException("SNMP packet too short.");
}
// Reset scoped pdu specific variables
_contextEngineId.Reset();
_contextName.Reset();
// parse scoped pdu specific variables
offset = _contextEngineId.decode(buffer, offset);
offset = _contextName.decode(buffer, offset);
// decode base pdu
offset = base.decode(buffer, offset);
return(offset);
}
/// <summary>BER encode security model field.</summary>
/// <remarks>
/// USM security model is a SEQUENCE encoded inside a OCTETSTRING. To encode it, first encode the sequence
/// of class values then "wrap" it inside a OCTETSTRING field
/// </remarks>
/// <param name="buffer">Buffer to store encoded USM security model header</param>
public override void encode(MutableByte buffer)
{
MutableByte tmp = new MutableByte();
// First encode all the values that will form the sequence
_engineId.encode(tmp);
// Encode engine boots
_engineBoots.encode(tmp);
// encode engine time
_engineTime.encode(tmp);
_securityName.encode(tmp);
if (_authentication != AuthenticationDigests.None)
{
if (_authenticationParameters.Length <= 0)
{
// If authentication is used, set authentication parameters field to 12 bytes set to 0x00
_authenticationParameters.Set(new byte[] { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 });
}
}
else
{
_authenticationParameters.Reset();
}
_authenticationParameters.encode(tmp);
if (_privacy != PrivacyProtocols.None)
{
if (_privacyParameters.Length <= 0)
{
IPrivacyProtocol privProto = PrivacyProtocol.GetInstance(_privacy);
if (privProto != null)
{
byte[] parameter = new byte[privProto.PrivacyParametersLength];
for (int i = 0; i < privProto.PrivacyParametersLength; i++)
{
parameter[i] = 0x00; // This is not necessary since all array members are, by default, initialized to 0
}
_privacyParameters.Set(parameter);
}
else
{
throw new SnmpException(SnmpException.UnsupportedPrivacyProtocol, "Unrecognized privacy protocol specified.");
}
}
}
else
{
_privacyParameters.Reset();
}
_privacyParameters.encode(tmp);
MutableByte tmp1 = new MutableByte();
BuildHeader(tmp1, SnmpConstants.SMI_SEQUENCE, tmp.Length);
tmp1.Append(tmp);
BuildHeader(buffer, OCTETSTRING, tmp1.Length);
buffer.Append(tmp1);
}