One document matched: draft-ietf-bfd-hmac-sha-04.xml
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<rfc category="std" docName="draft-ietf-bfd-hmac-sha-04" ipr="trust200902">
<front>
<title abbrev="BFD HMAC-SHA">Authenticating BFD using HMAC-SHA-2
procedures</title>
<author fullname="Dacheng Zhang" initials="D." surname="Zhang">
<organization>Huawei</organization>
<address>
<postal>
<street/>
<city>Beijing</city>
<region/>
<code/>
<country>China</country>
</postal>
<email>zhangdacheng@huawei.com</email>
</address>
</author>
<author fullname="Manav Bhatia " initials="M." surname="Bhatia ">
<organization>Alcatel-Lucent</organization>
<address>
<postal>
<street/>
<city>Bangalore</city>
<code>560045</code>
<country>India</country>
</postal>
<email>manav.bhatia@alcatel-lucent.com</email>
</address>
</author>
<author fullname="Vishwas Manral " initials="V. " surname="Manral ">
<organization>Hewlett-Packard Co.</organization>
<address>
<postal>
<street>19111 Pruneridge Ave.</street>
<city>Cupertino</city>
<region>CA</region>
<code>95014</code>
<country>USA</country>
</postal>
<email>vishwas.manral@hp.com</email>
</address>
</author>
<date day="15" month="October" year="2013"/>
<abstract>
<t>This document describes the mechanism to authenticate Bidirectional
Forwarding Detection (BFD) protocol packets using Hashed Message
Authentication Mode (HMAC) with the SHA-256, SHA-384, and SHA-512
algorithms. The described mechanism uses the Generic Cryptographic
Authentication and Generic Meticulous Cryptographic Authentication
sections to carry the authentication data. This document updates, but
does not supercede, the cryptographic authentication mechanism specified
in RFC 5880.</t>
</abstract>
<note title="Requirements Language">
<t>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 <xref
target="RFC2119">RFC 2119</xref>.</t>
</note>
</front>
<middle>
<section title="Introduction">
<t>The cryptographic authentication mechanisms specified in <xref
target="RFC5880"/> defines MD5 <xref target="RFC1321"/> and Secure Hash
Algorithm (SHA-1) algorithms to authenticate BFD packets. The recent
escalating series of attacks on MD5 and SHA-1 <xref
target="SHA-1-attack1"/> <xref target="SHA-1-attack2"/> raise concerns
about their remaining useful lifetime <xref target="RFC6151"/> <xref
target="RFC6194"/>.</t>
<t>These attacks may not necessarily result in direct vulnerabilities
for Keyed-MD5 and Keyed-SHA-1 digests as message authentication codes
because the colliding message may not correspond to a syntactically
correct BFD protocol packet. Regardless, there is a need felt to
deprecate MD5 and SHA-1 as the basis for the HMAC algorithm in favor of
stronger digest algorithms.</t>
<t>This document adds support for Secure Hash Algorithms (SHA) defined
in the US NIST Secure Hash Standard (SHS), which is defined by NIST FIPS
180-2 <xref target="FIPS-180-2"/>. <xref target="FIPS-180-2"/> includes
SHA-1, SHA-224, SHA-256, SHA-384, and SHA-512. The HMAC authentication
mode defined in NIST FIPS 198 is used <xref target="FIPS-198"/>.</t>
<t>It is believed that the HMAC algorithms defined in <xref
target="RFC2104"/> is mathematically identical to their counterparts in
<xref target="FIPS-198"/> and it is also believed that algorithms in
<xref target="RFC6234"/> are mathematically identical to those defined
in <xref target="FIPS-180-2"/>.</t>
<t>It should be noted that the collision attacks currently known against
SHA-1 do not apply when SHA-1 is used in the HMAC construction. NIST
will be supporting HMAC-SHA-1 even after 2010 <xref
target="NIST-HMAC-SHA"/> , whereas it would be dropping support for
SHA-1 in digital signatures.</t>
<t><xref target="I-D.ietf-bfd-generic-crypto-auth"/> defines new
authentication types - Generic Cryptographic Authentication and Generic
Meticulous Cryptographic Authentication that can be used for carrying
the authentication digests defined in this document.</t>
<t>Implementations of this specification must include support for at
least HMAC-SHA-256 and may include support for either of HMAC-SHA-384 or
HMAC-SHA-512.</t>
</section>
<section title="Cryptographic Aspects ">
<t>In the algorithm description below, the following nomenclature, which
is consistent with <xref target="FIPS-198"/>, is used:</t>
<t>H is the specific hashing algorithm (e.g. SHA-256).</t>
<t>K is the password for the BFD packet.</t>
<t>Ko is the cryptographic key used with the hash algorithm.</t>
<t>B is the block size of H, measured in octets rather than bits. Note
that B is the internal block size, not the hash size. For SHA-1 and
SHA-256: B == 64 For SHA-384 and SHA-512: B == 128 L is the length of
the hash, measured in octets rather than bits.</t>
<t>XOR is the exclusive-or operation.</t>
<t>Opad is the hexadecimal value 0x5c repeated B times.</t>
<t>Ipad is the hexadecimal value 0x36 repeated B times.</t>
<t>Apad is the hexadecimal value 0x878FE1F3 repeated (L/4) times.</t>
<t>(1) Preparation of the Key</t>
<t>In this application, Ko is always L octets long.</t>
<t>If the Authentication Key (K) is L octets long, then Ko is equal to
K. If the Authentication Key (K) is more than L octets long, then Ko is
set to H(K). If the Authentication Key (K) is less than L octets long,
then Ko is set to the Authentication Key (K) with zeros appended to the
end of the Authentication Key (K) such that Ko is L octets long.</t>
<t>(2) First Hash</t>
<t>First, the Authentication Data field in the Generic Authentication
Section is filled with the value of Apad and the Authentication Type
field is set to 6 or 7 depending upon which Authentication Type is being
used. The Sequence Number field MUST be set to bfd.XmitAuthSeq.</t>
<t>Then, a first hash, also known as the inner hash, is computed as
follows:</t>
<t>First-Hash = H(Ko XOR Ipad || (BFD Packet))</t>
<t>(3) Second Hash T</t>
<t>Then a second hash, also known as the outer hash, is computed as
follows:</t>
<t>Second-Hash = H(Ko XOR Opad || First-Hash)</t>
<t>(4) Result</t>
<t>The resultant Second-Hash becomes the Authentication Data that is
sent in the Authentication Data field of the BFD Authentication Section.
The length of the Authentication Data field is always identical to the
message digest size of the specific hash function H that is being
used.</t>
<t>This also means that the use of hash functions with larger output
sizes will also increase the size of BFD Packet as transmitted on the
wire.</t>
</section>
<section title="Procedures at the Sending Side ">
<t>Before a BFD device sends a BFD packet out, the device needs to
select an appropriate BFD SA from its local key table if a keyed digest
for the packet is required. If no appropriate SA is avaliable, the BFD
packet MUST be discarded.</t>
<t>If an appropriate SA is avaliable, the device then derives the key
and the associated authentication algorithm (HMAC-SHA-256, HMAC-SHA-384
or HMAC-SHA-512) from the SA.</t>
<t>The device then start performing the operations illustrated in
Section 2. Before the authentication data is computed, the device MUST
fill the Auth Type field and the Auth length field. The Sequence Number
field MUST be set to bfd.XmitAuthSeq.</t>
<t>The value of Auth Length in the generic authentication section is
various according to different authentication algorithms being used.
Specifically, the value is 40 for HMAC-SHA-256, 56 for HMAC-SHA-384, and
72 for HMAC- SHA-512.</t>
<t>The Key ID is then filled.</t>
<t>After that, the authentication data is computed as illustrated in
Section 2.</t>
<t>The result of the authentication algorithm is placed in the
Authentication data, following the Key ID.</t>
</section>
<section title="Procedure at the Receiving Side ">
<t>Upon receiving a BFD packet with an generic authentication section
appended, a device needs to find an appropriate BFD SA from its local
key table to verify the packet. The SA is located by the Key ID in the
authentication section of the packet.</t>
<t>If there is no SA is associated with the Key ID, the received packet
MUST be discarded.</t>
<t>If bfd.AuthSeqKnown is 1, the Sequence Number field is examined. For
Cryptographic Authentication, if the Sequence Number lies outside of the
range of bfd.RcvAuthSeq to bfd.RcvAuthSeq+(3*Detect Mult) inclusive
(when treated as an unsigned 32 bit circular number space), the received
packet MUST be discarded. For Meticulous Cryptographic Authentication,
if the Sequence Number lies outside of the range of bfd.RcvAuthSeq+1 to
bfd.RcvAuthSeq+(3*Detect Mult) inclusive (when treated as an unsigned 32
bit circular number space, the received packet MUST be discarded.</t>
<t>An authentication Algorithm dependent process then needs to be
performed by using the algorithm specified by the appropriate BFD SA for
the received packet.</t>
<t>Before the device performs any processing, it needs to save the
content of the Authentication Value field and set the Authentication
Value field with Apad.</t>
<t>The device then computes the authentication data as illustrated in
Section 2. The calculated data is compared with the received
authentication data in the packet.</t>
<t>The packet MUST be discarded if the calculated and the received
authentication data do not match. In this case, an error event SHOULD be
logged.</t>
<t>A BFD implementation MAY be in a transition mode where it includes
CRYPTO_AUTH or the MET_CRYPTO_AUTH information in packets but never
verifies it. This is provided as a transition aid for networks in the
process of migrating to the new CRYPTO_AUTH and MET_CRYPTO_AUTH based
authentication schemes.</t>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>This document makes no request of IANA.</t>
<t>Note to RFC Editor: this section may be removed on publication as an
RFC.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>The approach described in this document enhances the security of the
BFD protocol by adding, to the existing BFD cryptographic authentication
methods, support for the SHA-2 algorithms defined in the NIST Secure
Hash Standard (SHS) using the HMAC mode. However, the confidentiality
protection for BFD packets is out of scope of this work .</t>
<t>Because all of the currently specified algorithms use symmetric
cryptography, one cannot authenticate precisely which BFD device sent a
given packet. However, one can authenticate that the sender knew the BFD
Security Association (including the BFD SA's parameters) currently in
use.</t>
<t>To enhance system security, the applied keys should be changed
periodically and implementations SHOULD be able to store and use more
than one key at the same time. The quality of the security provided by
the cryptographic authentication option depends completely on the
strength of the cryptographic algorithm and cryptographic mode in use,
the strength of the key being used, and the correct implementation of
the security mechanism in all communicating BFD implementations.
Accordingly, the use of high assurance development methods is
recommended. It also requires that all parties maintain the secrecy of
the shared secret key. <xref target="RFC4086"/> provides guidance on
methods for generating cryptographically random bits.</t>
<t>The value Apad is used here primarily for consistency with IETF
specifications for HMAC-SHA authentication for RIPv2 <xref
target="RFC4822"/>, IS-IS <xref target="RFC5310"/> and OSPFv2 <xref
target="RFC5709"/>.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include='reference.RFC.6151'?>
<?rfc include='reference.RFC.6194'?>
<?rfc include='reference.RFC.6039'?>
<?rfc include='reference.I-D.ietf-bfd-generic-crypto-auth'?>
<reference anchor="FIPS-180-2">
<front>
<title>The Keyed-Hash Message Authentication Code (HMAC)</title>
<author fullname="" surname="">
<organization>National Institute of Standards and Technology, FIPS
PUB 180-2</organization>
</author>
<date month="August" year="2002"/>
</front>
</reference>
<reference anchor="FIPS-198">
<front>
<title>The Keyed-Hash Message Authentication Code (HMAC)</title>
<author>
<organization>National Institute of Standards and Technology, FIPS
PUB 198</organization>
</author>
<date month="March" year="2002"/>
</front>
</reference>
</references>
<references title="Informative References">
<?rfc include='reference.I-D.ietf-karp-design-guide'?>
<reference anchor="MD5-attack">
<front>
<title>Collisions for Hash Functions MD4, MD5, HAVAL-128 and
RIPEMD</title>
<author initials="X" surname="Wang">
<organization/>
</author>
<author fullname="" initials="D." surname="Feng">
<organization/>
<address>
<postal>
<street/>
<city/>
<region/>
<code/>
<country/>
</postal>
<phone/>
<facsimile/>
<email/>
<uri/>
</address>
</author>
<author initials="X." surname="Lai">
<organization/>
<address>
<postal>
<street/>
<city/>
<region/>
<code/>
<country/>
</postal>
<phone/>
<facsimile/>
<email/>
<uri/>
</address>
</author>
<author initials="H." surname="Yu">
<organization/>
<address>
<postal>
<street/>
<city/>
<region/>
<code/>
<country/>
</postal>
<phone/>
<facsimile/>
<email/>
<uri/>
</address>
</author>
<date month="August" year="2004"/>
</front>
</reference>
<reference anchor="Dobb96a">
<front>
<title>Cryptanalysis of MD5 Compress</title>
<author initials="H." surname="Dobbertin">
<organization/>
</author>
<date month="May" year="1996"/>
</front>
</reference>
<reference anchor="NIST-HMAC-SHA">
<front>
<title>NIST's Policy on Hash Functions</title>
<author fullname="" surname="">
<organization>National Institute of Standards and Technology,
Available online at
http://csrc.nist.gov/groups/ST/hash/policy.html</organization>
</author>
<date month="" year="2006"/>
</front>
</reference>
<reference anchor="Dobb96b">
<front>
<title>The Status of MD5 After a Recent Attack", CryptoBytes</title>
<author initials="H." surname="Dobbertin">
<organization/>
</author>
<date year="1996"/>
</front>
</reference>
<reference anchor="SHA-1-attack1">
<front>
<title>Finding Collisions in the Full SHA-1</title>
<author initials="X." surname="Wang">
<organization/>
</author>
<author initials="Y." surname="Yin">
<organization/>
<address>
<postal>
<street/>
<city/>
<region/>
<code/>
<country/>
</postal>
<phone/>
<facsimile/>
<email/>
<uri/>
</address>
</author>
<author initials="H." surname="Yu">
<organization/>
<address>
<postal>
<street/>
<city/>
<region/>
<code/>
<country/>
</postal>
<phone/>
<facsimile/>
<email/>
<uri/>
</address>
</author>
<date year="2005"/>
</front>
</reference>
<reference anchor="SHA-1-attack2">
<front>
<title>New Collision Search for SHA-1</title>
<author initials="X." surname="Wang">
<organization/>
</author>
<author initials="A." surname="Yao">
<organization/>
<address>
<postal>
<street/>
<city/>
<region/>
<code/>
<country/>
</postal>
<phone/>
<facsimile/>
<email/>
<uri/>
</address>
</author>
<author initials="F." surname="Yao">
<organization/>
<address>
<postal>
<street/>
<city/>
<region/>
<code/>
<country/>
</postal>
<phone/>
<facsimile/>
<email/>
<uri/>
</address>
</author>
<date year="2005"/>
</front>
</reference>
<?rfc include='reference.RFC.2104'?>
<?rfc include='reference.RFC.5880'?>
<?rfc include='reference.RFC.4086'?>
<?rfc include='reference.RFC.4822'?>
<?rfc include='reference.RFC.5310'?>
<?rfc include='reference.RFC.5709'?>
<?rfc include='reference.RFC.1321'?>
<?rfc include='reference.RFC.6234'?>
</references>
</back>
</rfc>
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