/// <summary>Generate privacy key from authentication password and engine id</summary>
/// <returns>Privacy key on success or null on failure</returns>
public byte[] GeneratePrivacyKey()
{
if (userSecurityModel.Authentication == AuthenticationDigests.None)
{
return(null);
}
if (userSecurityModel.Privacy == EPrivacyProtocols.None)
{
return(null);
}
if (userSecurityModel.PrivacySecret == null || userSecurityModel.PrivacySecret.Length <= 0)
{
return(null);
}
IAuthenticationDigest authProto = Authentication.GetInstance(userSecurityModel.Authentication);
if (authProto != null)
{
IPrivacyProtocol privProto = PrivacyProtocol.GetInstance(userSecurityModel.Privacy);
if (privProto != null)
{
return(privProto.PasswordToKey(userSecurityModel.PrivacySecret, userSecurityModel.EngineId, authProto));
}
}
return(null);
}
/// <summary>Encode SNMP version 3 packet</summary>
/// <remarks>
/// Before encoding the packet into a byte array you need to ensure all required information is
/// set. Examples of required information is request type, Vbs (Oid + values pairs), USM settings including
/// SecretName, authentication method and secret (if needed), privacy method and secret (if needed), etc.
/// </remarks>
/// <returns>Byte array BER encoded SNMP packet.</returns>
public override byte[] Encode()
{
byte[] pkey = null;
byte[] akey = null;
if (messageFlags.Authentication && userSecurityModel.EngineId.Length > 0)
{
IAuthenticationDigest auth = Authentication.GetInstance(userSecurityModel.Authentication);
if (auth == null)
{
throw new SnmpException(SnmpException.EErrorCode.UnsupportedNoAuthPriv, "Invalid authentication protocol.");
}
akey = auth.PasswordToKey(userSecurityModel.AuthenticationSecret, userSecurityModel.EngineId);
if (messageFlags.Privacy && userSecurityModel.EngineId.Length > 0)
{
IPrivacyProtocol privacyProtocol = PrivacyProtocol.GetInstance(userSecurityModel.Privacy);
if (privacyProtocol == null)
{
throw new SnmpException(SnmpException.EErrorCode.UnsupportedPrivacyProtocol, "Specified privacy protocol is not supported.");
}
pkey = privacyProtocol.PasswordToKey(userSecurityModel.PrivacySecret, userSecurityModel.EngineId, auth);
}
}
return(Encode(akey, pkey));
}
/// <summary>Build cached authentication and privacy encryption keys if they are appropriate for the selected security mode.</summary>
/// <remarks>
/// This method should be called after discovery process has been completed and all security related values
/// have been set. For noAuthNoPriv, none of the keys are generated. authNoPriv will result in authentication
/// key cached. authPriv will generate authentication and privacy keys.
///
/// For successful key caching you need to set both relevant protocols and secret values.
/// </remarks>
public void BuildCachedSecurityKeys()
{
authenticationKey = privacyKey = null;
if (engineId == null || engineId.Length <= 0)
{
return;
}
if (authenticationSecret == null || authenticationSecret.Length <= 0)
{
return;
}
if (authenticationProtocol != AuthenticationDigests.None)
{
IAuthenticationDigest authProto = Security.Authentication.GetInstance(authenticationProtocol);
if (authProto != null)
{
authenticationKey = authProto.PasswordToKey(authenticationSecret, engineId);
if (privacyProtocol != EPrivacyProtocols.None && privacySecret != null && privacySecret.Length > 0)
{
IPrivacyProtocol privProto = PrivacyProtocol.GetInstance(privacyProtocol);
if (privProto != null)
{
privacyKey = privProto.PasswordToKey(privacySecret, engineId, authProto);
}
}
}
}
}
/// <summary>
/// Build cached authentication and privacy encryption keys if they are appropriate for the selected security mode.
/// </summary>
/// <remarks>
/// This method should be called after discovery process has been completed and all security related values
/// have been set. For noAuthNoPriv, none of the keys are generated. authNoPriv will result in authentication
/// key cached. authPriv will generate authentication and privacy keys.
///
/// For successful key caching you need to set both relevant protocols and secret values.
/// </remarks>
public void BuildCachedSecurityKeys()
{
_authenticationKey = _privacyKey = null;
if (_engineId == null || _engineId.Length <= 0)
{
return;
}
if (_authenticationSecret == null || _authenticationSecret.Length <= 0)
{
return;
}
if (_authenticationProtocol != AuthenticationDigests.None)
{
IAuthenticationDigest authProto = SnmpSharpNet.Authentication.GetInstance(_authenticationProtocol);
if (authProto != null)
{
_authenticationKey = authProto.PasswordToKey(_authenticationSecret, _engineId);
if (_privacyProtocol != PrivacyProtocols.None && _privacySecret != null && _privacySecret.Length > 0)
{
IPrivacyProtocol privProto = PrivacyProtocol.GetInstance(_privacyProtocol);
if (privProto != null)
{
_privacyKey = privProto.PasswordToKey(_privacySecret, _engineId, authProto);
}
}
}
}
}
/// <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)
{
byte[] pkey = null;
byte[] akey = null;
if (MsgFlags.Authentication && USM.EngineId.Length > 0)
{
IAuthenticationDigest auth = Authentication.GetInstance(USM.Authentication);
if (auth == null)
{
throw new SnmpException(SnmpException.UnsupportedNoAuthPriv, "Invalid authentication protocol.");
}
akey = auth.PasswordToKey(USM.AuthenticationSecret, USM.EngineId);
if (MsgFlags.Privacy && USM.EngineId.Length > 0)
{
IPrivacyProtocol privacyProtocol = PrivacyProtocol.GetInstance(USM.Privacy);
if (privacyProtocol == null)
{
throw new SnmpException(SnmpException.UnsupportedPrivacyProtocol, "Specified privacy protocol is not supported.");
}
pkey = privacyProtocol.PasswordToKey(USM.PrivacySecret, USM.EngineId, auth);
}
}
return(Decode(berBuffer, length, akey, pkey));
}
/// <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);
}
/// <summary>Encode SNMP version 3 packet</summary>
/// <param name="authKey">Authentication key (not password)</param>
/// <param name="privKey">Privacy key (not password)</param>
/// <remarks>
/// Before encoding the packet into a byte array you need to ensure all required information is
/// set. Examples of required information is request type, Vbs (Oid + values pairs), USM settings including
/// SecretName, authentication method and secret (if needed), privacy method and secret (if needed), etc.
/// </remarks>
/// <returns>Byte array BER encoded SNMP packet.</returns>
public byte[] Encode(byte[] authKey, byte[] privKey)
{
MutableByte buffer = new MutableByte();
// encode the global message data sequence header information
MutableByte globalMessageData = new MutableByte();
// if message id is 0 then generate a new, random message id
if (messageId.Value == 0)
{
Random rand = new Random();
messageId.Value = rand.Next(1, int.MaxValue);
}
// encode message id
messageId.Encode(globalMessageData);
// encode max message size
maxMessageSize.Encode(globalMessageData);
// message flags
messageFlags.Encode(globalMessageData);
// security model code
securityModel.Value = userSecurityModel.Type;
securityModel.Encode(globalMessageData);
// add global message data to the main buffer
// encode sequence header and add data
AsnType.BuildHeader(buffer, SnmpConstants.SmiSequence, globalMessageData.Length);
buffer.Append(globalMessageData);
MutableByte packetHeader = new MutableByte(buffer);
// before going down this road, check if this is a discovery packet
OctetString savedUserName = new OctetString();
bool privacy = messageFlags.Privacy;
bool authentication = messageFlags.Authentication;
bool reportable = messageFlags.Reportable;
if (userSecurityModel.EngineId.Length <= 0)
{
// save USM settings prior to encoding a Discovery packet
savedUserName.Set(userSecurityModel.SecurityName);
userSecurityModel.SecurityName.Reset(); // delete security name for discovery packets
messageFlags.Authentication = false;
messageFlags.Privacy = false;
messageFlags.Reportable = true;
}
userSecurityModel.Encode(buffer);
if (userSecurityModel.EngineId.Length <= 0)
{
// restore saved USM values
userSecurityModel.SecurityName.Set(savedUserName);
messageFlags.Authentication = authentication;
messageFlags.Privacy = privacy;
messageFlags.Reportable = reportable;
}
// Check if privacy encryption is required
MutableByte encodedPdu = new MutableByte();
if (messageFlags.Privacy && userSecurityModel.EngineId.Length > 0)
{
IPrivacyProtocol privacyProtocol = PrivacyProtocol.GetInstance(userSecurityModel.Privacy);
if (privacyProtocol == null)
{
throw new SnmpException(SnmpException.EErrorCode.UnsupportedPrivacyProtocol, "Specified privacy protocol is not supported.");
}
// Get BER encoded ScopedPdu
MutableByte unencryptedPdu = new MutableByte();
scopedPdu.Encode(unencryptedPdu);
// we have to expand the key
IAuthenticationDigest auth = Authentication.GetInstance(userSecurityModel.Authentication);
if (auth == null)
{
throw new SnmpException(SnmpException.EErrorCode.UnsupportedNoAuthPriv, "Invalid authentication protocol. noAuthPriv mode not supported.");
}
byte[] encryptedBuffer = privacyProtocol.Encrypt(unencryptedPdu, 0, unencryptedPdu.Length, privKey, userSecurityModel.EngineBoots, userSecurityModel.EngineTime, out byte[] privacyParameters, auth);
userSecurityModel.PrivacyParameters.Set(privacyParameters);
OctetString encryptedOctetString = new OctetString(encryptedBuffer);
encryptedOctetString.Encode(encodedPdu);
// now redo packet encoding
buffer.Reset();
buffer.Set(packetHeader);
userSecurityModel.Encode(buffer);
int preEncodedLength = encodedPdu.Length;
buffer.Append(encodedPdu);
if (maxMessageSize.Value != 0)
{
// verify compliance with maximum message size
if ((encodedPdu.Length - preEncodedLength) > maxMessageSize)
{
throw new SnmpException(SnmpException.EErrorCode.MaximumMessageSizeExceeded, "ScopedPdu exceeds maximum message size.");
}
}
}
else
{
scopedPdu.Encode(encodedPdu);
buffer.Append(encodedPdu);
}
Encode(buffer);
if (messageFlags.Authentication && userSecurityModel.EngineId.Length > 0)
{
userSecurityModel.Authenticate(authKey, ref buffer);
// Now re-encode the packet with the authentication information
userSecurityModel.Encode(packetHeader);
packetHeader.Append(encodedPdu);
Encode(packetHeader);
buffer = packetHeader;
}
return(buffer);
}
/// <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>
/// Encode SNMP version 3 packet
/// </summary>
/// <remarks>
/// Before encoding the packet into a byte array you need to ensure all required information is
/// set. Examples of required information is request type, Vbs (Oid + values pairs), USM settings including
/// SecretName, authentication method and secret (if needed), privacy method and secret (if needed), etc.
/// </remarks>
/// <returns>Byte array BER encoded SNMP packet.</returns>
public override byte[] encode()
{
MutableByte buffer = new MutableByte();
// encode the global message data sequence header information
MutableByte globalMessageData = new MutableByte();
// if message id is 0 then generate a new, random message id
if (_messageId.Value == 0)
{
Random rand = new Random();
_messageId.Value = rand.Next(1, Int32.MaxValue);
}
// encode message id
_messageId.encode(globalMessageData);
// encode max message size
_maxMessageSize.encode(globalMessageData);
// message flags
_msgFlags.encode(globalMessageData);
// security model code
_securityModel.Value = _userSecurityModel.Type;
_securityModel.encode(globalMessageData);
// add global message data to the main buffer
// encode sequence header and add data
AsnType.BuildHeader(buffer, SnmpConstants.SMI_SEQUENCE, globalMessageData.Length);
buffer.Append(globalMessageData);
MutableByte packetHeader = new MutableByte(buffer);
// before going down this road, check if this is a discovery packet
OctetString savedUserName = new OctetString();
bool privacy = _msgFlags.Privacy;
bool authentication = _msgFlags.Authentication;
bool reportable = _msgFlags.Reportable;
if (_userSecurityModel.EngineId.Length <= 0)
{
// save USM settings prior to encoding a Discovery packet
savedUserName.Set(_userSecurityModel.SecurityName);
_userSecurityModel.SecurityName.Reset(); // delete security name for discovery packets
_msgFlags.Authentication = false;
_msgFlags.Privacy = false;
_msgFlags.Reportable = true;
}
_userSecurityModel.encode(buffer);
if (_userSecurityModel.EngineId.Length <= 0)
{
// restore saved USM values
_userSecurityModel.SecurityName.Set(savedUserName);
_msgFlags.Authentication = authentication;
_msgFlags.Privacy = privacy;
_msgFlags.Reportable = reportable;
}
// Check if privacy encryption is required
MutableByte encodedPdu = new MutableByte();
if (_msgFlags.Privacy && _userSecurityModel.EngineId.Length > 0)
{
IPrivacyProtocol privacyProtocol = PrivacyProtocol.GetInstance(_userSecurityModel.Privacy);
if (privacyProtocol == null)
{
throw new SnmpException(SnmpException.UnsupportedPrivacyProtocol, "Specified privacy protocol is not supported.");
}
// Get BER encoded ScopedPdu
MutableByte unencryptedPdu = new MutableByte();
_scopedPdu.encode(unencryptedPdu);
byte[] privacyParameters = null;
// we have to expand the key
IAuthenticationDigest auth = Authentication.GetInstance(_userSecurityModel.Authentication);
if (auth == null)
{
throw new SnmpException(SnmpException.UnsupportedNoAuthPriv, "Invalid authentication protocol. noAuthPriv mode not supported.");
}
byte[] pkey = privacyProtocol.PasswordToKey(_userSecurityModel.PrivacySecret, _userSecurityModel.EngineId, auth);
byte[] encryptedBuffer = privacyProtocol.Encrypt(unencryptedPdu, 0, unencryptedPdu.Length, pkey, _userSecurityModel.EngineBoots, _userSecurityModel.EngineTime, out privacyParameters, auth);
_userSecurityModel.PrivacyParameters.Set(privacyParameters);
OctetString encryptedOctetString = new OctetString(encryptedBuffer);
encryptedOctetString.encode(encodedPdu);
// now redo packet encoding
buffer.Reset();
buffer.Set(packetHeader);
_userSecurityModel.encode(buffer);
int preEncodedLength = encodedPdu.Length;
buffer.Append(encodedPdu);
if (_maxMessageSize.Value != 0)
{
// verify compliance with maximum message size
if ((encodedPdu.Length - preEncodedLength) > _maxMessageSize)
{
throw new SnmpException(SnmpException.MaximumMessageSizeExceeded, "ScopedPdu exceeds maximum message size.");
}
}
}
else
{
_scopedPdu.encode(encodedPdu);
buffer.Append(encodedPdu);
}
int preVersionLength = buffer.Length;
base.encode(buffer);
int versionHeaderLength = buffer.Length - preVersionLength;
if (_msgFlags.Authentication && _userSecurityModel.EngineId.Length > 0)
{
_userSecurityModel.Authenticate(ref buffer);
// Now re-encode the packet with the authentication information
_userSecurityModel.encode(packetHeader);
packetHeader.Append(encodedPdu);
base.encode(packetHeader);
buffer = packetHeader;
}
return(buffer);
}
/// <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);
}