TCP Increased Security
charter-ietf-tcpinc-00-03

The TCPINC WG will develop the TCP extensions to provide unauthenticated
encryption and integrity protection of TCP streams. The WG will define an
unauthenticated key exchange mechanism. In addition, the WG will define the TCP
extensions to utilize unauthenticated keys, resulting in encryption and
integrity protection without authentication. This is better than plain-text
because it thwarts passive eavesdropping, but is weaker than using authenticated
keys, because it is vulnerable to man-in-the-middle attacks during the initial
unathenticated key exchange. This work is part of the IETF effort to harness the
Internet architecture given the latest events of pervasive monitoring (see BCP
188).

The goal of this WG is to provide an additional security tool that complements
existing protocols at other layers in the stack. The WG will be looking for the
designs that find the right tradeoff spot between conflicting requirements: to
provide reasonable security for the majority of connections. Because we are
dealing with unprotected connections, we are more focussed on improving from
baseline of no security than achieving the high standard of security that is
already available to users of TLS. Providing unauthenticated encryption and
integrity protection at the TCP layer will provide a set of features that cannot
be achieved with existing tools, namely, encryption and integrity protection
without modifications to the upper ayers (no API changes), encryption and
integrity protection with forward secrecy with a per-connection granularity,
simple NAT and firewall traversal capabilities, key rollover without significant
impact to the TCP connection, lower overhead compared to solutions relying in
stacking multiple protocols to achieve different features, no manual
configuration required. A more detailed description of the motivations for
TCP-based solutions can be found in draft-bellovin-tcpsec-01 and in RFC5925.

The working group is looking to produce experimental documents specifying the
required TCP extensions and any additional documents needed.

The high-level requirements for the protocol for providing TCP unauthenticated
encryption and integrity protection are:

• It should work over the vast majority of paths that unmodified TCP works over,
  in particular it must be compatible with NATs (at the very minimum with the
  NATs that comply with BEHAVE requirements as documented in RFC4787, RFC5382 and
  RFC5508);

• The protocol must be usable by unmodified applications. This effort is
  complementary to other security protocols developed in the IETF (such as TLS)
  as it protects those applications and protocols that are difficult to change or
  may even not be changed in a backward compatible way. It also provides some
  protection in scenarios where people are unwilling to do any change just for the
  sake of security (e.g., like configure encryption in an application).

• The protocol must provide cryptographic algorithm agility.

• Must gracefully fall-back to TCP if the remote peer does not support the
  proposed extensions

• When encryption is enabled, it must at least provide protection against
  passive eavesdropping by default,

• Should attempt to use the least amount of TCP option space, especially in SYN
  segments.

• Must not require any authentication or configuration from applications or
  users. However, hooks for external authentication must be made available.
  The WG will not work on new authentication mechanisms.

• The protocol must have acceptable performance, including acceptable latency
  and processing overheads. For example, the protocol may try to re-use
  existing cryptographic material for future communication between the same
  endpoints to avoid expensive public key operations on connection set up.

When encryption is enabled, then the protocol:

• must always provide forward secrecy.

• must always provide integrity protection of the payload data (it is open for
  discussion for the WG if the TCP header should or not be protected)

• must always provide payload encryption.

• must not provide extra linkability. When encryption is enabled the TCP traffic
  should not give a third party observer any extra way to associate those
  packets with the specific peers beyond information that would have been present
  in a cleartext session.

• must allow the initiator of the connection to avoid fingerprinting: some
  initiators may want to avoid appearing as the same endpoint when connecting to
  a remote peer on subsequent occasions. This should either be the default or some
  mechanism should be available for initiators to drop or ignore shared state to
  avoid being fingerprintable any more than would be present for a cleartext
  session.

Security features at the TCP-level can benefit other TCP extensions. For
example, both Multipath TCP and TCP Fast Open require proof that some
connections are related. Session resumption and Message Authentication Codes
(MACs) can provide this evidence. The working group should identify synergies
and design the security protocol in such a way that other TCP efforts can
benefit from it. Of course, TCP extensions that break must be identified too,
and kept to a minimum.

The working group will produce the following documents:

• A framework for unauthenticated encryption and integrity protection of TCP
  connections. This document will describe basic design considerations,
  including the motivation and the applicability of the proposed mechanism, the
  interaction with other security mechanisms in different layers of the stack, the
  interaction with external authentication mechanisms, the expected protection,
  privacy considerations and residual threats.

• Definition of the unauthenticated key exchange mechanism and the extensions to
  current TCP to utilize unauthenticated key to provide encryption and integrity
  protection. This covers all the protocol changes required. This will be an
  experimental document.

• An extended API describing how applications can obtain further benefits of
  the proposed extensions. In particular, the hooks for supporting external
  authentication will be defined in this document. This will be an informational
  document.