ISAKMP Protocol

Requirement: Accept how many transforms should be included in the proposal and the values
for the transform IDs from the user. Include these into the formats given below and pass them
to the server. The server should choose one of the transforms and reply with only that transform
in the message. Repeat this for the number of times accepted as a command line argument.

Proposal Payload

   The Proposal Payload contains information used during Security
   Association negotiation.  The proposal consists of security
   mechanisms, or transforms, to be used to secure the communications
   channel.  Figure 6 shows the format of the Proposal Payload.  

                          1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ! Next Payload  !   RESERVED    !         Payload Length        !
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     !  Proposal #   !  Protocol-Id  !    SPI Size   !# of Transforms!
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     !                        SPI (variable)                         !
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                 Figure 6:  Proposal Payload Format

   The Proposal Payload fields are defined as follows:

    o  Next Payload (1 octet) - Identifier for the payload type of the
       next payload in the message.  This field MUST only contain the
       value "2" or "0".  If there are additional Proposal payloads in
       the message, then this field will be 2.  If the current Proposal
       payload is the last within the security association proposal,
       then this field will be 0.

    o  RESERVED (1 octet) - Unused, set to 0.

    o  Payload Length (2 octets) - Length in octets of the entire
       Proposal payload, including generic payload header, the Proposal
       payload, and all Transform payloads associated with this
       proposal.

    o  Proposal # (1 octet) - Identifies the Proposal number for the
       current payload.

    o  Protocol-Id (1 octet) - Specifies the protocol identifier for the
       current negotiation.  Examples might include IPSEC ESP, IPSEC AH,
       OSPF, TLS, etc.

    o  SPI Size (1 octet) - Length in octets of the SPI as defined by
       the Protocol-Id. This value should be 4.

    o  # of Transforms (1 octet) - Specifies the number of transforms
       for the Proposal.  Each of these is contained in a Transform
       payload.

    o  SPI (variable) - The sending entity's SPI. This is a user input
       - an unsigned long.

   The payload type for the Proposal Payload is two (2).

Transform Payload

   The Transform Payload contains information used during Security
   Association negotiation.  The Transform payload consists of a
   specific security mechanism, or transforms, to be used to secure the
   communications channel.  The Transform payload also contains the
   security association attributes associated with the specific
   transform.  These SA attributes are DOI-specific.  Figure 7 shows the
   format of the Transform Payload.

                          1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ! Next Payload  !   RESERVED    !         Payload Length        !
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     !  Transform #  !  Transform-Id !           RESERVED2           !
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 7:  Transform Payload Format

   The Transform Payload fields are defined as follows:

    o  Next Payload (1 octet) - Identifier for the payload type of the
       next payload in the message.  This field MUST only contain the
       value "3" or "0".  If there are additional Transform payloads in
       the proposal, then this field will be 3.  If the current
       Transform payload is the last within the proposal, then this
       field will be 0.

    o  RESERVED (1 octet) - Unused, set to 0.

    o  Payload Length (2 octets) - Length in octets of the current
       payload, including the generic payload header, Transform values,
       and all SA Attributes.

    o  Transform # (1 octet) - Identifies the Transform number for the
       current payload.  If there is more than one transform proposed
       for a specific protocol within the Proposal payload, then each
       Transform payload has a unique Transform number.

    o  Transform-Id (1 octet) - Specifies the Transform identifier for
       the protocol within the current proposal.  These transforms are
       defined by the DOI and are dependent on the protocol being
       negotiated. Transform ID can be either 1, 2 or 3.

    o  RESERVED2 (2 octets) - Unused, set to 0.

Group 11 :
Implement it as a TCP iterative server with select

Group 12 :
Implement it as a TCP concurrent server with threads