Network Working Group K. Grewal Internet Draft Intel Corporation Intended status: Standards Track G. Montenegro Expires: February 06, 2010 Microsoft Corporation M. Bhatia Alcatel-Lucent August 06, 2009 Wrapped ESP for Traffic Visibility draft-ietf-ipsecme-traffic-visibility-06.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on February 06, 2010. Copyright Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license- info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Grewal, et. al. Expires February 06, 2010 [Page 1] Internet-Draft WESP For Traffic Visibility August 2009 Abstract This document describes the Wrapped Encapsulating Security Payload (WESP) protocol, which builds on top of Encapsulating Security Payload (ESP) [RFC4303] and is designed to allow intermediate devices to ascertain if ESP-NULL [RFC2410] is being employed and hence inspect the IPsec packets for network monitoring and access control functions. Currently in the IPsec standard, there is no way to differentiate between ESP encryption and ESP NULL encryption by simply examining a packet. This poses certain challenges to the intermediate devices that need to deep inspect the packet before making a decision on what should be done with that packet (Inspect and/or Allow/Drop). The mechanism described in this document can be used to easily disambiguate ESP-NULL from ESP encrypted packets, without compromising on the security provided by ESP. Table of Contents 1. Introduction...................................................2 1.1. Requirements Language.....................................4 1.2. Applicability Statement...................................4 2. Wrapped ESP (WESP) Header format...............................4 2.1. UDP Encapsulation.........................................7 2.2. Transport and Tunnel Mode Considerations..................8 2.2.1. Transport Mode Processing............................8 2.2.2. Tunnel Mode Processing...............................9 2.3. IKE Considerations.......................................10 3. Security Considerations.......................................11 4. IANA Considerations...........................................12 5. Acknowledgments...............................................12 6. References....................................................12 6.1. Normative References.....................................12 6.2. Informative References...................................13 1. Introduction Use of ESP within IPsec [RFC4303] specifies how ESP packet encapsulation is performed. It also specifies that ESP can use NULL encryption while preserving data integrity and authenticity. The exact encapsulation and algorithms employed are negotiated out-of-band using, for example, IKEv2 [RFC4306] and based on policy. Enterprise environments typically employ numerous security policies (and tools for enforcing them), as related to access control, content screening, firewalls, network monitoring functions, deep packet inspection, Intrusion Detection and Grewal, et. al. Expires February 06 2010 [Page 2] Internet-Draft WESP For Traffic Visibility August 2009 Prevention Systems (IDS and IPS), scanning and detection of viruses and worms, etc. In order to enforce these policies, network tools and intermediate devices require visibility into packets, ranging from simple packet header inspection to deeper payload examination. Network security protocols which encrypt the data in transit prevent these network tools from performing the aforementioned functions. When employing IPsec within an enterprise environment, it is desirable to employ ESP instead of AH [RFC4302], as AH does not work in NAT environments. Furthermore, in order to preserve the above network monitoring functions, it is desirable to use ESP- NULL. In a mixed mode environment some packets containing sensitive data employ a given encryption cipher suite, while other packets employ ESP-NULL. For an intermediate device to unambiguously distinguish which packets are leveraging ESP-NULL, they would require knowledge of all the policies being employed for each protected session. This is clearly not practical. Heuristic-based methods can be employed to parse the packets, but these can be very expensive, containing numerous rules based on each different protocol and payload. Even then, the parsing may not be robust in cases where fields within a given encrypted packet happen to resemble the fields for a given protocol or heuristic rule. This is even more problematic when different length Initialization Vectors (IVs), Integrity Check Values (ICVs) and padding are used for different security associations, making it difficult to determine the start and end of the payload data, let alone attempting any further parsing. Furthermore, storage, lookup and cross-checking a set of comprehensive rules against every packet adds cost to hardware implementations and degrades performance. In cases where the packets may be encrypted, it is also wasteful to check against heuristics-based rules, when a simple exception policy (e.g., allow, drop or redirect) can be employed to handle the encrypted packets. Because of the non-deterministic nature of heuristics- based rules for disambiguating between encrypted and non- encrypted data, an alternative method for enabling intermediate devices to function in encrypted data environments needs to be defined. Additionally there are many types and classes of network devices employed within a given network and a deterministic approach would provide a simple solution for all these devices. Enterprise environments typically use both stateful and stateless packet inspection mechanisms. The previous considerations weigh particularly heavy on stateless mechanisms such as router ACLs and NetFlow exporters. Nevertheless, a deterministic approach provides a simple solution for the myriad types of devices employed within a network, regardless of their stateful or stateless nature. Grewal, et. al. Expires February 06 2010 [Page 3] Internet-Draft WESP For Traffic Visibility August 2009 This document defines a mechanism to provide additional information in relevant IPsec packets so intermediate devices can efficiently differentiate between encrypted ESP packets and ESP packets with NULL encryption. The document is consistent with the operation of ESP in NAT environments [RFC3947]. The design principles for this protocol are the following: o Allow easy identification and parsing of integrity-only IPsec traffic o Leverage the existing hardware IPsec parsing engines as much as possible to minimize additional hardware design costs o Minimize the packet overhead in the common case 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 1.2. Applicability Statement The document is applicable only to the wrapped ESP header defined below, and does not describe any changes to either ESP [RFC4303] nor IP Authentication Header (AH) [RFC4302]. 2. Wrapped ESP (WESP) Header format Wrapped ESP encapsulation (WESP) uses protocol number (TBD via IANA) different from AH and ESP. Accordingly, the (outer) protocol header (IPv4, IPv6, or Extension) that immediately precedes the WESP header SHALL contain the value (TBD via IANA) in its Protocol (IPv4) or Next Header (IPv6, Extension) field. WESP provides additional attributes in each packet to assist in differentiating between encrypted and non-encrypted data, and to aid parsing of the packet. WESP follows RFC 4303 for all IPv6 and IPv4 considerations (e.g., alignment considerations). This extension essentially acts as a wrapper to the existing ESP protocol and provides an additional 4 octets at the front of the existing ESP packet. This may be depicted as follows: Grewal, et. al. Expires February 06 2010 [Page 4] Internet-Draft WESP For Traffic Visibility August 2009 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Wrapped ESP Header | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Existing ESP Encapsulation | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1 WESP Packet Format By preserving the body of the existing ESP packet format, a compliant implementation can simply add in the new header, without needing to change the body of the packet. The value of the new protocol used to identify this new header is TBD via IANA. Further details are shown below: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | HdrLen | TrailerLen | Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Existing ESP Encapsulation | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2 Detailed WESP Packet Format Where: Next Header, 8 bits: This field MUST be the same as the Next Header field in the ESP trailer when using ESP in the Integrity only mode, and MUST be set to zero when using ESP with Encryption. The receiver MUST do some sanity checks before the WESP packet is accepted. 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 zero if using WESP with encryption. The WESP flags dictate if the packet is encrypted and/or integrity protected. 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) within the encapsulated ESP header, in octets. The Grewal, et. al. Expires February 06 2010 [Page 5] Internet-Draft WESP For Traffic Visibility August 2009 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 doesn't match. TrailerLen, 8 bits: Offset from the end of the packet to the last byte of the payload data 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 2 bits: Version. MUST be sent as 0 and checked by the receiver. Future modifications to the WESP header may require a new version number. 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). 1 bit: Encrypted Payload. 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 ESP-NULL cipher. Setting or clearing this 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. 5 bits: Flags, reserved for future use. The flags MUST be sent as 0, and ignored by the receiver. Future documents defining any of these flags MUST NOT affect the distinction between encrypted and unencrypted packets. Intermediate nodes dealing with unknown flags 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 Flag bits sent, possibly by negotiating them over the control channel. The receiver MUST drop packets for which the integrity check is invalid. As can be seen, the WESP format extends the standard ESP header by the first 4 octets. The WESP header is integrity protected, along with all the fields specified for ESP in RFC 4303. Grewal, et. al. Expires February 06 2010 [Page 6] Internet-Draft WESP For Traffic Visibility August 2009 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. 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 3 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. Grewal, et. al. Expires February 06 2010 [Page 7] Internet-Draft WESP For Traffic Visibility August 2009 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. In the diagrams below, "WESP ICV" refers to the ICV computation as modified by this specification. Namely, the ESP ICV computation is augmented to include the four octets that constitute the WESP header. Otherwise, the ICV computation is as specified by ESP [RFC4303]. 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 -------->| Grewal, et. al. Expires February 06 2010 [Page 8] Internet-Draft WESP For Traffic Visibility August 2009 AFTER APPLYING WESP - IPv4 -------------------------------------------------------- |orig IP hdr | WESP | ESP | | | ESP |WESP| |(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 |WESP| |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. 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. Grewal, et. al. Expires February 06 2010 [Page 9] Internet-Draft WESP For Traffic Visibility August 2009 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 |WESP| |(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 |WESP| |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. 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 Grewal, et. al. Expires February 06 2010 [Page 10] Internet-Draft WESP For Traffic Visibility August 2009 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) MAY be included in a request message that also includes an SA payload requesting a CHILD_SA using ESP. It 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. 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 to in determining appropriate security policy for the given traffic streams and data over which it is being employed. 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. Grewal, et. al. Expires February 06 2010 [Page 11] Internet-Draft WESP For Traffic Visibility August 2009 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. 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]. The final 6 bits of the WESP Flags are the "Non-version Flags". This specification defines no values, and future assignment is to be managed via the IANA Policy of "Specification Required". 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, Men Long, David Durham, Prashant Dewan, Marc Millier among others. This document was prepared using 2-Word-v2.0.template.doc. 6. References 6.1. Normative References [RFC2410] Glenn, R. and S. Kent, "The NULL Encryption Algorithm and Its Use With IPsec", RFC 2410, November 1998. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, December 2005. Grewal, et. al. Expires February 06 2010 [Page 12] Internet-Draft WESP For Traffic Visibility August 2009 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. [RFC3948] Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M. Stenberg, "UDP Encapsulation of IPsec ESP Packets", RFC 3948, January 2005. [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, December 2005. [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC 4306, December 2005. [RFC5226] Narten, T., Alverstrand, H., "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 5226, May 2008. Author's Addresses Ken Grewal Intel Corporation 2111 NE 25th Avenue, JF3-232 Hillsboro, OR 97124 USA Phone: Email: ken.grewal@intel.com Grewal, et. al. Expires February 06 2010 [Page 13] Internet-Draft WESP For Traffic Visibility August 2009 Gabriel Montenegro Microsoft Corporation One Microsoft Way Redmond, WA 98052 USA Phone: Email: gabriel.montenegro@microsoft.com Manav Bhatia Alcatel-Lucent Bangalore India Phone: Email: manav@alcatel-lucent.com Grewal, et. al. Expires February 06 2010 [Page 14]