Optimizing BFD AuthenticationCisco Systems170 W. Tasman DriveSan JoseCA95134USA+1 (408) 526-8763mjethanandani@gmail.comCiena Corporation3939 North 1st StreetSan JoseCA95134USAmishra.ashesh@gmail.comCiena Corporation3939 N 1st StreetSan JoseCA95134USAankurpsaxena@gmail.comIonos NetworksBangaloreIndiamanavbhatia@gmail.comThis document describes an optimization to BFD Authentication as
described in Section 6.7 of BFD [RFC5880].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.Authenticating every BFD packet with a
Simple Password, or with a MD5 Message-Digest
Algorithm , or Secure Hash Algorithm (SHA-1) algorithms is
computationally intensive process, making it difficult if not impossible
to authenticate every packet - particularly at faster rates. Also, the
recent escalating series of attacks on MD5 and SHA-1 raise concerns
about their remaining useful lifetime as outlined in Updated Security Considerations for the MD5
Message-Digest and the HMAC-MD5 Algorithm and Security Considerations for the SHA-0 and SHA-1
Message-Digest Algorithm . If replaced by stronger algorithms,
the computational overhead, will make the task of authenticating every
packet even more difficult to achieve.This document proposes that only BFD frames that signal a state
change in BFD be authenticated. Rest of the frames can be transmitted
and received without authentication enabled. Most frames that are
transmitted and received have no state change associated with them.
Limiting authentication to frames that affect a BFD session state allows
more sessions to be supported for authentication. Moreover, most BFD
frames that signal a state change are generally transmitted at a slower
interval of 1s leaving enough time to compute the hash.Section 2 talks about the changes to authentication mode as described
in BFD.The cryptographic authentication mechanisms specified in BFD describes enabling and disabling of
authentication as a one time operation. As a security precaution, it
mentions that authentication state be allowed to change at most once.
Once enabled, every packet must have Authentication Bit set and the
associated Authentication TLV appended. In addition, it states that an
implementation SHOULD NOT allow the authentication state to be changed
based on the receipt of a BFD Control packet.This document proposes that the authentication mode be modified to be
enabled on demand. Instead of authenticating every packet, BFD peers
decide which frames need to be authenticated, and authenticate only
those frames. For example, the two ends can decide that BFD frames that
indicate a state change should be authenticated and enable
authentication on those frames only. If the two ends have not previously
negotiated which frames they will transmit or receive with
authentication enabled, then the BFD session will fail to come up,
because at least one end will expect every frame to be authenticated.
The state changes for which authentication is being suggested
include:All frames already carry the sequence number. The NULL AUTH frames
MUST contain the TLV specified in Section 3. This enables a
monotonically increasing sequence number to be carried in each frame,
and prevents man-in-the-middle from capturing and replaying the same
frame again. Since all frames still carry a sequence number, the logic
for sequence number maintenance remains unchanged from . If at a later time, a different scheme is adopted
for changing sequence number, this method can use the updated scheme
without any impact.Most frames transmitted on a BFD session are BFD CC UP frames.
Authenticating a small subset of these frames (one per configured
period) significantly reduces the computational demand for the system
while maintaining security of the session across the configured
authentication periods. The configuration of the periodic authentication
interval for BFD CC UP frames is an open issue.This section describes a new Authentication TLV as: where:Auth Type: The Authentication Type, which in this case is 0 (NULL
Auth TL)Auth Len: The length of the NULL Auth TLV, in bytes i.e. 8 bytesAuth Key ID: The authentication key ID in use for this packet. Must
be set to zero.Reserved: The authentication key ID in use for this packet. This
allows multiple keys to be active simultaneously.Sequence Number: The sequence number for this packet. This value is
incremented for each successive packet transmitted for a session. This
provides protection against replay attacks. Must use the same sequence
number counter as the authenticated frames. The NULL Auth TLV must be used for all frames that are not
authenticated. This protects against replay-attacks by allowing the
session to maintain an incrementing sequence number for all frames
(authenticated and un-authenticated).In the future, if a new scheme is adopted for changing the sequence
number, this method can adopt the new scheme without any impact.This document requests an update to the registry titled "BFD
Authentication Types". IANA is requested to update the Value of 0 which
is currently named as Reserved to NULL (see Section 3).Note to RFC Editor: this section may be removed on publication as an
RFC.The approach described in this document enhances the ability to
authentication a BFD session by taking away the onerous requirement that
every frame be authenticated. By authenticating frames that affect the
state of the session, the security of the BFD session is maintained. As
such this document does not change the security considerations for
BFD.The Keyed-Hash Message Authentication Code (HMAC)National Institute of Standards and Technology, FIPS
PUB 180-2The Keyed-Hash Message Authentication Code (HMAC)National Institute of Standards and Technology, FIPS
PUB 198Collisions for Hash Functions MD4, MD5, HAVAL-128 and
RIPEMDCryptanalysis of MD5 CompressNIST's Policy on Hash FunctionsNational Institute of Standards and Technology,
Available online at
http://csrc.nist.gov/groups/ST/hash/policy.htmlThe Status of MD5 After a Recent Attack", CryptoBytesFinding Collisions in the Full SHA-1New Collision Search for SHA-1