Wrapped Encapsulating Security Payload (ESP) for Traffic Visibility
draft-ietf-ipsecme-traffic-visibility-12

quot; 
   field looses this name and semantics and becomes an empty field 
   which MUST be initialized to all zeros. The receiver MUST do 
   some sanity checks before the WESP packet is accepted. The 
   receiver MUST ensure that the Next Header field in the WESP 
   header and the Next Header field in the ESP trailer match when 
   using ESP in the Integrity only mode. The packet MUST be dropped 
   if the two do not match. Similarly, the receiver MUST ensure 
   that the Next Header field in the WESP header is an empty field 
   initialized to zero if using WESP with encryption. The WESP 
   flags dictate if the packet is encrypted.  
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   HdrLen, 8 bits: Offset from the beginning of the WESP header to 
   the beginning of the Rest of Payload Data (i.e., past the IV, if 
   present and any other WESP options defined in future) within the 
   encapsulated ESP header, in octets. HdrLen MUST be set to zero 
   when using ESP with encryption. When using integrity-only ESP, 
   the following HdrLen values are invalid: any value less than 12; 
   any value that is not a multiple of 4; any value that is not a 
   multiple of 8 when using IPv6. The receiver MUST ensure that 
   this field matches with the header offset computed from using 
   the negotiated SA and MUST drop the packet in case it does not 
   match.  

   TrailerLen, 8 bits: TrailerLen contains the size of the ICV 
   being used by the negotiated algorithms within the IPsec SA, in 
   octets. TrailerLen MUST be set to zero when using ESP with 
   encryption. The receiver MUST only accept the packet if this 
   field matches with the value computed from using the negotiated 
   SA. This insures that sender is not deliberately setting this 
   value to obfuscate a part of the payload from examination by a 
   trusted intermediary device. 

   Flags, 8 bits: The bits are defined most-significant-bit (MSB) 
   first, so bit 0 is the most significant bit of the flags octet. 

   0 1 2 3 4 5 6 7 
  +-+-+-+-+-+-+-+-+ 
  |V V|E|P| Rsvd  | 
  +-+-+-+-+-+-+-+-+ 
   
   Figure 3 Flags format 

       Version (V), 2 bits: MUST be sent as 0 and checked by the 
   receiver. If the version is different than an expected version 
   number (e.g. negotiated via the control channel), then the 
   packet MUST be dropped by the receiver. Future modifications to 
   the WESP header require a new version number. In particular, the 
   version of WESP defined in this document does not allow for any 
   extensions. However, old implementations will still be able to 
   find the encapsulated cleartext packet using the HdrLen field 
   from the WESP header, when the 'E' bit is not set. Intermediate 
   nodes dealing with unknown versions are not necessarily able to 
   parse the packet correctly. Intermediate treatment of such 
   packets is policy-dependent (e.g., it may dictate dropping such 
   packets).  

       Encrypted Payload (E), 1 bit: Setting the Encrypted Payload 
   bit to 1 indicates that the WESP (and therefore ESP) payload is 
   protected with encryption. If this bit is set to 0, then the 
   payload is using integrity-only ESP. Setting or clearing this 
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   bit also impacts the value in the WESP Next Header field, as 
   described above. The recipient MUST ensure consistency of this 
   flag with the negotiated policy and MUST drop the incoming 
   packet otherwise.    

      Padding header (P), 1 bit: If set (value 1), the 4 octet 
   padding is present. If not set (value 0), the 4 octet padding 
   is absent. This padding MUST be used with IPv6 in order to 
   preserve IPv6 8-octet alignment. If WESP is being used with UDP 
   encapsulation (see 2.1 below) and IPv6, the Protocol Identifier 
   (0x00000002) occupies four octets so the IPv6 padding is not 
   needed, as the header is already on an 8-octet boundary. This 
   padding MUST NOT be used with IPv4, as it is not needed to 
   guarantee 4-octet IPv4 alignment.  

       Rsvd, 4 bits: Reserved for future use.  The reserved bits 
   MUST be sent as 0, and ignored by the receiver. Future documents 
   defining any of these bits MUST NOT affect the distinction 
   between encrypted and unencrypted packets or the semantics of 
   HdrLen. In other words, even if new bits are defined, old 
   implementations will be able to find the encapsulated packet 
   correctly. Intermediate nodes dealing with unknown reserved bits 
   are not necessarily able to parse the packet correctly. 
   Intermediate treatment of such packets is policy-dependent 
   (e.g., it may dictate dropping such packets).  

   Future versions of this protocol may change the version number 
   and/or the reserved bits sent, possibly by negotiating them over 
   the control channel.  

   As can be seen, the WESP format extends the standard ESP header 
   by the first 4 octets for IPv4 and optionally (see above) by 8 
   octets for IPv6.  

2.1. UDP Encapsulation 

   This section describes a mechanism for running the new packet 
   format over the existing UDP encapsulation of ESP as defined in 
   RFC 3948. This allows leveraging the existing IKE negotiation of 
   the UDP port for NAT-T discovery and usage [RFC3947, RFC4306], 
   as well as preserving the existing UDP ports for ESP (port 
   4500).  With UDP encapsulation, the packet format can be 
   depicted as follows.  

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   0                   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 
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
  |        Src Port (4500)        | Dest Port (4500)              | 
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
  |             Length            |          Checksum             | 
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
  |          Protocol Identifier (value = 0x00000002)             | 
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
  |  Next Header  |   HdrLen      |  TrailerLen   |    Flags      |  
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
  |                      Existing ESP Encapsulation               | 
  ~                                                               ~ 
  |                                                               | 
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
    
                Figure 4 UDP-Encapsulated WESP Header 

   Where: 

   Source/Destination port (4500) and checksum: describes the UDP 
   encapsulation header, per RFC3948. 

   Protocol Identifier: new field to demultiplex between UDP 
   encapsulation of IKE, UDP encapsulation of ESP per RFC 3948, and  
   the UDP encapsulation in this specification. 

   According to RFC 3948, clause 2.2, a 4 octet value of zero (0) 
   immediately following the UDP header indicates a Non-ESP marker, 
   which can be used to assume that the data following that value 
   is an IKE packet.  Similarly, a value greater then 255 indicates 
   that the packet is an ESP packet and the 4-octet value can be 
   treated as the ESP SPI. However, RFC 4303, clause 2.1 indicates 
   that the values 1-255 are reserved and cannot be used as the 
   SPI.  We leverage that knowledge and use one of these reserved 
   values to indicate that the UDP encapsulated ESP header contains 
   this new packet format for ESP encapsulation. 

   The remaining fields in the packet have the same meaning as per 
   section 2 above. 

2.2. Transport and Tunnel Mode Considerations 

   This extension is equally applicable to transport and tunnel mode 
   where the ESP Next Header field is used to differentiate between 
   these modes, as per the existing IPsec specifications.  

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2.2.1. Transport Mode Processing 

   In transport mode, ESP is inserted after the IP header and before a 
   next layer protocol, e.g., TCP, UDP, ICMP, etc. The following 
   diagrams illustrate how WESP is applied to the ESP transport mode for 
   a typical packet, on a "before and after" basis.  

  BEFORE APPLYING WESP -IPv4 
        -------------------------------------------------     
        |orig IP hdr  | ESP |     |      |   ESP   | ESP|                
        |(any options)| Hdr | TCP | Data | Trailer | ICV| 
        ------------------------------------------------- 
                            |<---- encryption ---->| 
                      |<------- integrity -------->| 
    

  AFTER APPLYING WESP - IPv4 
        --------------------------------------------------------     
        |orig IP hdr  | WESP | ESP |     |      |   ESP   | ESP|                
        |(any options)| Hdr  | Hdr | TCP | Data | Trailer | ICV| 
        -------------------------------------------------------- 
                                   |<---- encryption ---->| 
                             |<------- integrity -------->| 
   
   
  BEFORE APPLYING WESP - IPv6 
      -------------------------------------------------------------- 
      | orig |hop-by-hop,dest*,|   |dest|   |    | ESP   | ESP| 
      |IP hdr|routing,fragment.|ESP|opt*|TCP|Data|Trailer| ICV| 
      -------------------------------------------------------------- 
                                   |<---- encryption --->| 
                               |<----- integrity ------->| 
   
  AFTER APPLYING WESP - IPv6 
      -------------------------------------------------------------- 
      | orig |hop-by-hop,dest*,|    |   |dest|   |    | ESP   | ESP| 
      |IP hdr|routing,fragment.|WESP|ESP|opt*|TCP|Data|Trailer| ICV| 
      -------------------------------------------------------------- 
                                        |<---- encryption --->| 
                                    |<----- integrity ------->| 
   
                  
               * = if present, could be before WESP, after ESP, or both 
    

   All other considerations are as per RFC 4303. 

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2.2.2. Tunnel Mode Processing 

   In tunnel mode, ESP is inserted after the new IP header and before 
   the original IP header, as per RFC 4303. The following diagram 
   illustrates how WESP is applied to the ESP tunnel mode for a typical 
   packet, on a "before and after" basis. 

  BEFORE APPLYING WESP - IPv4 
      --------------------------------------------------------- 
      |new IP hdr*  |   | orig IP hdr*  |   |    | ESP   | ESP| 
      |(any options)|ESP| (any options) |TCP|Data|Trailer| ICV| 
      --------------------------------------------------------- 
                        |<--------- encryption --------->| 
                    |<----------- integrity ------------>| 
                                         
  AFTER APPLYING WESP - IPv4 
      -------------------------------------------------------------- 
      |new IP hdr*  |    |   | orig IP hdr*  |   |    | ESP   | ESP| 
      |(any options)|WESP|ESP| (any options) |TCP|Data|Trailer| ICV| 
      -------------------------------------------------------------- 
                             |<--------- encryption --------->| 
                         |<----------- integrity ------------>| 
   
  BEFORE APPLYING WESP - IPv6 
  ----------------------------------------------------------------- 
  | new* |new ext |   | orig*|orig ext |   |    | ESP   | ESP| 
  |IP hdr| hdrs*  |ESP|IP hdr| hdrs *  |TCP|Data|Trailer| ICV| 
  ----------------------------------------------------------------- 
                      |<--------- encryption ---------->| 
                  |<------------- integrity ----------->| 
   
  AFTER APPLYING WESP - IPv6 
  ----------------------------------------------------------------- 
  | new* |new ext |    |   | orig*|orig ext |   |    | ESP   | ESP| 
  |IP hdr| hdrs*  |WESP|ESP|IP hdr| hdrs *  |TCP|Data|Trailer| ICV| 
  ----------------------------------------------------------------- 
                           |<--------- encryption ---------->| 
                       |<------------- integrity ----------->| 
   
                  
   * = if present, construction of outer IP hdr/extensions and 

   modification of inner IP hdr/extensions is discussed in 

   the Security Architecture document. 
    

   All other considerations are as per RFC 4303. 

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2.3. IKE Considerations 

   This document assumes that WESP negotiation is performed using 
   IKEv2. In order to negotiate the new format of ESP encapsulation 
   via IKEv2 [RFC4306], both parties need to agree to use the new 
   packet format. This can be achieved using a notification method 
   similar to USE_TRANSPORT_MODE defined in RFC 4306. 

   The notification, USE_WESP_MODE (value TBD) MUST be included in 
   a request message that also includes an SA payload requesting a 
   CHILD_SA using ESP.  It signals that the sender supports the 
   WESP version defined in the current document a requests that the 
   CHILD_SA use WESP mode rather than ESP for the SA created.  If 
   the request is accepted, the response MUST also include a 
   notification of type USE_WESP_MODE. If the responder declines 
   the request, the CHILD_SA will be established using ESP, as per 
   RFC 4303.  If this is unacceptable to the initiator, the 
   initiator MUST delete the SA.  Note: Except when using this 
   option to negotiate  WESP mode, all CHILD_SAs will use standard 
   ESP. 

   Negotiation of WESP in this manner preserves all other 
   negotiation parameters, including NAT-T [RFC3948]. NAT-T is 
   wholly compatible with this wrapped frame format and can be used 
   as-is, without any modifications, in environments where NAT is 
   present and needs to be taken into account. 

   WESP version negotiation is not introduced as part of this 
   specification. If the WESP version is updated in a future 
   specification, then that document MUST specify how the WESP 
   version is negotiated.  

3. Security Considerations 

   As this document augments the existing ESP encapsulation format, 
   UDP encapsulation definitions specified in RFC 3948 and IKE 
   negotiation of the new encapsulation, the security observations 
   made in those documents also apply here. In addition, as this 
   document allows intermediate device visibility into IPsec ESP 
   encapsulated frames for the purposes of network monitoring 
   functions, care should be taken not to send sensitive data over 
   connections using definitions from this document, based on 
   network domain/administrative policy. A strong key agreement 
   protocol, such as IKEv2, together with a strong policy engine 
   should be used in determining appropriate security policy for 
   the given traffic streams and data over which it is being 
   employed.  

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   ESP is end-to-end and it will be impossible for the intermediate 
   devices to verify that all the fields in the WESP header are 
   correct. It is thus possible to modify the WESP header so that 
   the packet sneaks past a firewall if the fields in the WESP 
   header are set to something that the firewall will allow. The 
   endpoint thus must verify the sanity of the WESP header before 
   accepting the packet. In an extreme case, someone colluding with 
   the attacker, could change the WESP fields back to the original 
   values so that the attack goes unnoticed. However, this is not a 
   new problem and it already exists IPsec. 

4. IANA Considerations 

   The WESP protocol number is assigned by IANA out of the IP 
   Protocol Number space (and as recorded at the IANA web page at 
   http://www.iana.org/assignments/protocol-numbers) is: TBD. 

   The USE_WESP_MODE notification number is assigned out of the 
   "IKEv2 Notify Message Types - Status Types" registry's 16384-
   40959 (Expert Review) range: TBD. 

   The SPI value of 2 is assigned by IANA out of the reserved SPI 
   range from the SPI values registry to indicate use of the WESP 
   protocol within a UDP encapsulated, NAT-T environment. 

   This specification requests that IANA create a new registry for 
   "WESP Flags" to be managed as follows: 

   The first 2 bits are the WESP Version Number. The value 0 is 
   assigned to the version defined in this specification. Further 
   assignments of the WESP Version Number are to be managed via the 
   IANA Policy of "Standards Action" [RFC5226]. For WESP version 
   numbers, the unassigned values are 1, 2 and 3. The Encrypted 
   Payload bit is used to indicate if the payload is encrypted or 
   using integrity-only ESP. The Padding Present bit is used to 
   signal the presence of padding. The remaining 4 bits of the WESP 
   Flags are undefined and future assignment is to be managed via 
   the IANA Policy of "IETF Review" [RFC5226]. 

    

5. Acknowledgments 

   The authors would like to acknowledge the following people for 
   their feedback on updating the definitions in this document. 

   David McGrew, Brian Weis, Philippe Joubert, Brian Swander, Yaron 
   Sheffer, Pasi Eronen, Men Long, David Durham, Prashant Dewan, 
   Marc Millier, Russ Housley, Jari Arkko among others. 
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   This document was prepared using 2-Word-v2.0.template.doc. 

6. References 

6.1. Normative References 

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate            
             Requirement Levels", BCP 14, RFC 2119, March 1997. 

   [RFC2410] Glenn, R. and Kent, S., "The NULL Encryption Algorithm 
             and Its Use With IPsec", RFC 2410, November 1998. 

   [RFC3948] Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and 
             M. Stenberg, "UDP Encapsulation of IPsec ESP Packets", 
             RFC 3948, January 2005. 

   [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",              
             RFC 4303, December 2005.  

   [RFC4543] McGrew, D. and Viega J., "The Use of Galois Message 
             Authentication Code (GMAC) in IPsec ESP and AH", RFC 
             4543, May 2006. 

   [RFC5226] Narten, T., Alverstrand, H., "Guidelines for Writing 
             an IANA Considerations Section in RFCs",  RFC 5226, 
             May 2008. 

6.2. Informative References 

   [RFC3947] Kivinen, T., Swander, B., Huttunen, A., and V. Volpe, 
             "Negotiation of NAT-Traversal in the IKE", RFC 3947, 
             January 2005. 

   [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, 
             December 2005. 

   [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",  
             RFC 4306, December 2005.  

    

   [Heuristics I-D] Kivinen, T., McDonald, D., "Heuristics for Detecting 
             ESP-NULL packets", Internet Draft, April 2009.  

     

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Author's Addresses 

   Ken Grewal 
   Intel Corporation 
   2111 NE 25th Avenue, JF3-232 
   Hillsboro, OR  97124 
   USA 
       
   Phone:  
   Email: ken.grewal@intel.com 
    

   Gabriel Montenegro 
   Microsoft Corporation 
   One Microsoft Way 
   Redmond, WA  98052 
   USA 
       
   Phone:  
   Email: gabriel.montenegro@microsoft.com 
    
   Manav Bhatia 
   Alcatel-Lucent 
   Manyata Embassy  
   Nagawara Bangalore 
    
   India 
    
   Phone: 
   Email: manav.bhatia@alcatel-lucent.com 

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