One document matched: draft-ietf-ipsecme-rfc4307bis-02.xml
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<rfc ipr="trust200902" docName="draft-ietf-ipsecme-rfc4307bis-02" category="std">
<front>
<title abbrev="IKEv2 Cryptographic Algorithms">Algorithm Implementation Requirements and Usage Guidance for IKEv2</title>
<author initials="Y." surname="Nir" fullname="Yoav Nir">
<organization abbrev="Check Point">Check Point Software Technologies Ltd.</organization>
<address>
<postal>
<street>5 Hasolelim st.</street>
<city>Tel Aviv</city>
<code>6789735</code>
<country>Israel</country>
</postal>
<email>ynir.ietf@gmail.com</email>
</address>
</author>
<author initials='T.' surname='Kivinen' fullname='Tero Kivinen'>
<organization>INSIDE Secure</organization>
<address>
<postal>
<street>Eerikinkatu 28</street>
<code>FI-00180</code>
<city>HELSINKI</city>
<country>FI</country>
</postal>
<email>kivinen@iki.fi</email>
</address>
</author>
<author fullname="Paul Wouters" initials="P." surname="Wouters">
<organization>Red Hat</organization>
<address>
<postal>
<street/>
<city/>
<region/>
<code/>
<country/>
</postal>
<email>pwouters@redhat.com</email>
</address>
</author>
<author fullname="Daniel Migault" initials="D." surname="Migault">
<organization> Ericsson </organization>
<address>
<postal>
<street> 8400 boulevard Decarie </street>
<city> Montreal, QC </city>
<code> H4P 2N2 </code>
<country> Canada </country>
</postal>
<phone> +1 514-452-2160 </phone>
<email> daniel.migault@ericsson.com </email>
</address>
</author>
<date year="2016"/>
<area>Security</area>
<!-- <workgroup>IPSecME Working Group</workgroup> -->
<keyword>Internet-Draft</keyword>
<abstract>
<t> The IPsec series of protocols makes use of various cryptographic algorithms in order to provide security
services. The Internet Key Exchange protocol provides a mechanism to negotiate which algorithms should be used
in any given Security Association. To ensure interoperability between different implementations, it is
necessary to specify a set of algorithm implementation requirements and Usage guidance to ensure that
there is at least one algorithm
that all implementations will have available. This document defines the current algorithm implementation
requirements and usage guidance of IKEv2. This document does not update the algorithms used for packet
encryption using IPsec Encapsulated Security Payload (ESP)</t>
</abstract>
</front>
<middle>
<!-- ====================================================================== -->
<section anchor="introduction" title="Introduction">
<t> The Internet Key Exchange protocol <xref target="RFC7296" /> is used to negotiate the IPsec parameters,
such as encryption algorithms and keys, for protected communications between two endpoints. The IKEv2 protocol
itself is also protected by encryption, which is also negotiated between the two endpoints. Negotiation
is performed by IKEv2 itself. This document describes the encryption parameters of the IKE protocol,
not the encryption parameters of the ESP (IPsec) protocol. Different implementations of IKEv2
may negotiate different encryption algorithms based on their individual local policy. To ensure interoperability,
a set of "mandatory-to-implement" IKEv2 encryption algorithms is defined. </t>
<section title="Updating Algorithm Implementation Requirements and Usage Guidance">
<t> The field of cryptography evolves continiously. New stronger algorithms appear and existing algorithms are found
to be less secure then originally thought. Therefore, algorithm implementation requirements and usage guidance need
to be updated from time to time to reflect the new reality. The choices for algorithms must be conservative
to minimize the risk of algorithm compromised. Algorithms need to be suitable for a wide variety of CPU architectures
and device deployments ranging from high end bulk encryption devices to small low-power IoT devices.</t>
<t> The algorithm implementation requirements and usage guidance may need to change over time to adapt
to the changing world. For this reason, the selection of mandatory-to-implement algorithms was removed
from the main IKEv2 specification and placed in this document. </t>
</section>
<section title="Updating Algorithm Requirement Levels">
<t> Ideally, the mandatory-to-implement algorithm of tomorrow should already be available in most implementations
of IKE by the time it is made mandatory. To facilitate this, this document attempts to identify those algorithms
for future mandatory-to-implement. There is no guarantee that the algorithms in use today may become mandatory
in the future. Published algorithms are continiously subjected to cryptographic attack and may become too weak or
could become completely broken before this document is updated.</t>
<t> This document only provides recommendations for the mandatory-to-implement algorithms or algorithms
too weak that are recommended not to be implemented. As a result, any algorithm not mentioned in this document
MAY be implemented. For clarification and consistency with <xref target="RFC4307"/> an algorithm will be set to
MAY only when it has been downgraded.</t>
<t> Although this document updates the algorithms in order to keep the IKEv2 communication secure over time,
it also aims at providing recommendations so that IKEv2 implementations remain interoperable. IKEv2 interoperability
is addressed by an incremental introduction or deprecation of algorithms. In addition, this document also considers
the new use cases for IKEv2 deployment, such as Internet of Things (IoT).</t>
<t> It is expected that deprecation of an algorithm is performed gradually. This provides time for various
implementations to update their implemented algorithms while remaining interoperable. Unless there are strong
security reasons, an algorithm is expected to be downgraded from MUST to MUST- or SHOULD, instead of MUST NOT.
Similarly, an algorithm that has not been mentioned as mandatory-to-implement is expected to be introduced with a
SHOULD instead of a MUST.</t>
<t>The current trend toward Internet of Things and its adoption of IKEv2 requires this specific use case to be taken
into account as well. IoT devices are resource constrainted devices and their choice of algorithms are motivated by
minimizing the fooprint of the code, the computation effort and the size of the messages to send. This document
indicates IoT when a specified algorithm is specifically listed for IoT devices.</t>
</section>
<section title="Document Audience">
<t>The recommendations of this document target IKEv2 implementers. In other words, the recommendations
should not be considered for IKEv2 configuration, as a preference for some algorithms.
[PAUL: I don't understand this. Clearly MTI are good default choices?] </t>
<t>IKEv1 is out of scope of this document. IKEv1 is deprecated and the recommendations of this document
must not be considered for IKEv1.</t>
</section>
</section>
<section anchor="mustshouldmay" title="Conventions Used in This Document">
<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"/>.</t>
<t> We define some additional terms here:</t>
<texttable anchor="tbl" style="none" suppress-title="true">
<ttcol align="left" width="12%"/>
<ttcol align="left" />
<c>SHOULD+</c><c>This term means the same as SHOULD. However, it is likely that an algorithm marked as SHOULD+
will be promoted at some future time to be a MUST.</c>
<c>SHOULD-</c><c>This term means the same as SHOULD. However, an algorithm marked as SHOULD- may be deprecated
to a MAY in a future version of this document.</c>
<c>MUST-</c><c>This term means the same as MUST. However, we expect at some point that this algorithm will no
longer be a MUST in a future document. Although its status will be determined at a later time, it is
reasonable to expect that if a future revision of a document alters the status of a MUST- algorithm, it will
remain at least a SHOULD or a SHOULD-.</c>
<c>IoT</c><c>stands for Internet of Things.</c>
</texttable>
</section>
<section anchor="algs" title="Algorithm Selection">
<section anchor="algs_enc" title="Type 1 - IKEv2 Encryption Algorithm Transforms">
<t> The algorithms in the below table are negotiated in the SA payload and used in the ENCR payload.
References to the specifications defining these algorithms and the ones in the following subsections are in
the IANA registry <xref target="IKEV2-IANA"/>. Some of these algorithms are Authenticated Encryption with
Associated Data (AEAD - <xref target="RFC5282" />). Algorithms that are not AEAD MUST be used in conjunction
with an integrity algorithms in <xref target="algs_integ"/>.</t>
<texttable anchor="tbl_enc" suppress-title="true">
<ttcol align="left">Name</ttcol>
<ttcol align="left">Status</ttcol>
<ttcol>AEAD?</ttcol>
<ttcol align="left">Comment</ttcol>
<c>ENCR_AES_CBC</c><c>MUST-</c><c>No</c><c>[1]</c>
<c>ENCR_CHACHA20_POLY1305</c><c>SHOULD</c><c>Yes</c><c/>
<c>AES-GCM with a 16 octet ICV</c><c>SHOULD</c><c>Yes</c><c>[1]</c>
<c>ENCR_AES_CCM_8</c><c>SHOULD</c><c>Yes</c><c>[1][IoT]</c>
<c>ENCR_3DES</c><c>MAY</c><c>No</c><c/>
<c>ENCR_DES</c><c>MUST NOT</c><c>No</c><c/>
<postamble>
[1] - This requirement level is for 128-bit keys. 256-bit keys are at MAY. 192-bit keys can
safely be ignored.
[IoT] - This requirement is for interoperability with IoT.
</postamble>
</texttable>
<t> ENCR_AES_CBC is raised from SHOULD+ in RFC4307. It is the only shared mandatory-to-implement algorithm
with RFC4307 and as a result is necessary for interoperability with IKEv2 implementation compatible with
RFC4307.</t>
<t> ENCR_CHACHA20_POLY1305 was not ready to be considered at the time of RFC4307.
It has been recommended by the CRFG and others as an alternative to AES and AES-GCM. It is also being
standarized for IPsec for the same reasons. At the time of writing, there were not enough IKEv2 implementations
of ENCR_CHACHA20_POLY1305 to be able to introduce it at the SHOULD+ level.</t>
<t> AES-GCM with a 16 octet ICV was not considered as in RFC4307. At the time RFC4307
was written, AES-GCM was not defined in an IETF document. AES-GCM was defined for ESP in
<xref target="RFC4106"/> and later for IKEv2 in <xref target="RFC5282"/>. The main motivation for adopting
AES-GCM for ESP is encryption performance as well as key longevity - compared to AES-CBC for example.
This resulted in AES-GCM widely implemented for ESP. As the load of IKEv2 is expected to remain
relatively small, many IKEv2 implementations do not include AES-GCM. In addition to its former MAY, this document
does not promote AES-GCM to a greater status than SHOULD so to preserve interoperability between IKEv2
implementations. [PAUL: I dont follow the reasoning, as we could have AES and AES-GCM at MUST level]
This document considers AES-GCM as mandatory to implement to promote the slightly more secure AEAD method
over the traditional encrypt+auth method. Its status is expected to be raised once widely deployed.</t>
<t> ENCR_AES_CCM_8 was not considered in RFC4307. This document considers it
SHOULD be implemented in order to be able to interact with Internet of Things devices. As this case is
not a general use case for VPNs, its status is expected to remain to SHOULD. The size of the ICV is
expected to be sufficient for most use cases of IKEv2, as far less packets are exchanged on the IKE_SA
compared to the IPsec SA. When implemented, ENCR_AES_CCM_8 MUST be implemented for key length 128 and
MAY be implemented for key length 256.</t>
<t> ENCR_3DES has been downgraded from RFC4307 MUST-. All IKEv2 implementation already implement
ENCR_AES_CBC, so there is no need to keep ENCR_3DES. In addition, ENCR_CHACHA20_POLY1305 provides a more
modern alternative to AES. [PAUL: removed 'efficient' as we said above encryption efficiency at the IKE
level hardly matters]</t>
<t> ENCR_DES can be brute-forced using of-the-shelves hardware. It provides no meaningful security
whatsoever and therefor MUST NOT be implemented.</t>
</section>
<section anchor="algs_prf" title="Type 2 - IKEv2 Pseudo-random Function Transforms">
<t> Transform Type 2 Algorithms are pseudo-random functions used to generate random values when needed.</t>
<t>In general, if you can trust an algorithm as INTEG algorithm, you can and should also use it as the PRF.
When using an AEAD cipher, the choice is PRF is open, and picking one of the SHA2 variants is recommended.</t>
<texttable anchor="tbl_alg2" suppress-title="true">
<ttcol align="left">Name</ttcol>
<ttcol align="left">Status</ttcol>
<ttcol align="left">Comment</ttcol>
<c>PRF_HMAC_SHA2_256</c><c>MUST</c><c></c>
<c>PRF_HMAC_SHA2_512</c><c>SHOULD+</c><c></c>
<c>PRF_HMAC_SHA1</c><c>MUST-</c><c>[1]</c>
<c>PRF_AES128_CBC</c><c>SHOULD</c><c>[IoT]</c>
<postamble>
[IoT] - This requirement is for interoperability with IoT
</postamble>
</texttable>
<t> PRF_HMAC_SHA2_256 was not mentioned in RFC4307, as no SHA2 based authentication was mentioned.
PRF_HMAC_SHA2_256 MUST be implemented in order to replace SHA1 and PRF_HMAC_SHA1.</t>
<t> PRF_HMAC_SHA2_512 SHOULD be implemented as as a future replacement of SHA2_256 or when stronger
security is required. PRF_HMAC_SHA2_512 is preferred over PRF_HMAC_SHA2_384, as the overhead of
PRF_HMAC_SHA2_512 is negligible.</t>
<t> PRF_HMAC_SHA1_96 has been downgraded from MUST in RFC4307.
There is an industry-wide trend to deprecate its usage.</t>
<t> PRF_AES128_CBC is only recommended in the scope of IoT, as Internet of Things deployments tend to
prefer AES based pseudo-random functions in order to avoid implementing SHA2. For the wide VPN
deployment, as it has not been widely adopted, it has been downgraded from SHOULD in RFC4307 to MAY.</t>
</section>
<section anchor="algs_integ" title="Type 3 - IKEv2 Integrity Algorithm Transforms">
<t> The algorithms in the below table are negotiated in the SA payload and used in the ENCR payload. References
to the specifications defining these algorithms are in the IANA registry. When an AEAD algorithm (see <xref
target="algs_enc"/>) is proposed, this algorithm transform type is not in use.</t>
<texttable anchor="tbl_alg3" suppress-title="true">
<ttcol align="left">Name</ttcol>
<ttcol align="left">Status</ttcol>
<ttcol align="left">Comment</ttcol>
<c>AUTH_HMAC_SHA2_256_128</c><c>MUST</c><c></c>
<c>AUTH_HMAC_SHA2_512_256</c><c>SHOULD</c><c></c>
<c>AUTH_HMAC_SHA1_96</c><c>SHOULD</c><c></c>
<c>AUTH_AES_XCBC_96</c><c>SHOULD</c><c>[IoT]</c>
<postamble>
[IoT] - This requirement is for interoperability with IoT
</postamble>
</texttable>
<t> AUTH_HMAC_SHA2_256_128 was not mentioned in RFC4307, as no SHA2 based authentication was mentioned.
AUTH_HMAC_SHA2_256_128 MUST be implemented in order to replace AUTH_HMAC_SHA1_96.</t>
<t> AUTH_HMAC_SHA2_512_256 SHOULD be implemented as as a future replacement of AUTH_HMAC_SHA2_256_128
or when stronger security is required. This value has been preferred to AUTH_HMAC_SHA2_384, as the overhead of
AUTH_HMAC_SHA2_512 is negligible.</t>
<t> AUTH_HMAC_SHA1_96 has been downgraded from MUST in RFC4307.
There is an industry-wide trend to deprecate its usage.</t>
<t> AUTH_AES-XCBC is only recommended in the scope of IoT, as Internet of Things deployments tend
to prefer AES based pseudo-random functions in order to avoid implementing SHA2. For the wide VPN
deployment, as it has not been widely adopted, it has been downgraded from SHOULD in RFC4307 to MAY.</t>
</section>
<section anchor="algs_dh" title="Type 4 - IKEv2 Diffie-Hellman Group Transforms">
<t> There are several Modular Exponential (MODP) groups and several Elliptic Curve groups (ECC) that are
defined for use in IKEv2. They are defined in both the [IKEv2] base document and in extensions documents.
They are identified by group number.</t>
<texttable anchor="tbl_dh" suppress-title="true">
<ttcol align="left">Number</ttcol>
<ttcol align="left">Description</ttcol>
<ttcol align="left">Status</ttcol>
<c>14</c><c>2048-bit MODP Group</c><c>MUST</c>
<c>19</c><c>256-bit random ECP group</c><c>SHOULD</c>
<c>5</c><c>1536-bit MODP Group</c><c>SHOULD NOT</c>
<c>2</c><c>1024-bit MODP Group</c><c>SHOULD NOT</c>
<c>1</c><c>768-bit MODP Group</c><c>MUST NOT</c>
<c>TBD</c><c>Curve25519</c><c>MAY</c>
</texttable>
<t> Group 14 or 2048-bit MODP Group is raised from SHOULD+ in RFC4307 as a replacement for
1024-bit MODP Group. Group 14 is widely implemented and considered secure</t>
<t> Group 19 or 256-bit random ECP group was not specified in RFC4307.
Group 19 is widely implemented and considered secure</t>
<t> Group 5 or 1536-bit MODP Group is downgrade from MUST- to SHOULD NOT. It was specified earlier,
but now considered to be vulnerable to be broken within the next few years by a nation state level attack,
so its security margin is considered too narrow.</t>
<t> Group 2 or 1024-bit MODP Group is downgrade from MUST- to SHOULD NOT.
It was specified earlier, but now it is known to be weak against sufficiently funded attackers using commercially
available mass-computing resources, so its security margin is considered too narrow. It is expected in the
near future to be downgraded to MUST NOT.</t>
<t> Group 1 or 768-bit MODP Group can be broken within hours using cheap of-the-shelves hardware. It provides
no security whatsoever.</t>
<t>Curve25519 has been designed with performance and security in mind and have been recommended by CFRG. At
the time of writing, the IKEv2 specification is still at the draft status. This document specifies it as to
encourage its implementation and deployment. If it gets widely implemented then it most likely will be
upgraded to SHOULD or even MUST in the future.</t>
</section>
</section>
<section title="IKEv2 Authentication">
<t>IKEv2 authentication may involve a signatures verification. Signatures may be used to validate a certificate
or to check the signature of the AUTH value. Cryptographic recommendations regarding certificate validation are out
of scope of this document as what mandatory implementations are provided by the PKIX WG. This document is mostly
concerned on signature verification and generation for the authentication.</t>
<section anchor="auth" title="IKEv2 Authentication Method">
<texttable anchor="tbl_auth" suppress-title="true">
<ttcol align="left">Number</ttcol>
<ttcol align="left">Description</ttcol>
<ttcol align="left">Status</ttcol>
<ttcol align="left">Comment</ttcol>
<c>1</c><c>RSA Digital Signature</c><c>MUST</c><c>With keys length 2048</c>
<c>1</c><c>RSA Digital Signature</c><c>SHOULD</c><c>With keys length 3072/4096</c>
<c>1</c><c>RSA Digital Signature</c><c>MUST NOT</c><c>With keys length lower than 2048</c>
<c>3</c><c>DSS Digital Signature</c><c>MAY</c><c></c>
<c>9</c><c>ECDSA with SHA-256 on the P-256 curve</c><c>SHOULD</c><c></c>
<c>10</c><c>ECDSA with SHA-384 on the P-384 curve</c><c>SHOULD</c><c></c>
<c>11</c><c>ECDSA with SHA-512 on the P-521 curve</c><c>SHOULD</c><c></c>
<c>14</c><c>Digital Signature</c><c>SHOULD</c><c></c>
</texttable>
<t>RSA Digital Signature is mostly kept for interoperability. It is expected to be downgraded
in the future as signatures are based on RSASSA-PKCS1-v1.5, not any more recommemded.
Instead, more robust use of RSA is expected to be performed via the Digital Signature method.</t>
<t>ECDSA family are also expected to be downgraded as it does not provide hash function agility.
Instead ECDSA is expected to be performed using the generic Digital Signature method.</t>
<t>DSS Digital Signature is bound to SHA-1 and thus is expected to be downgraded to MUST NOT in the future.</t>
<t>Digital Signature is expected to be promoted as it provides hash function, signature format and algorithm agility.</t>
<t>[MGLT: Do we have any recommendation for the authentication based on PSK?]</t>
</section>
<section title="Digital Signature Recommendation">
<t>Recommended methods: RSA (MUST), ECDSA (SHOULD), Ed25519 (MAY), Ed25519ph(MAY), Ed448(MAY), Ed448ph(MAY)?</t>
<t>Here are the recommendations when a hash function is involved in a signature.</t>
<texttable anchor="tbl_has" suppress-title="true">
<ttcol align="left">Number</ttcol>
<ttcol align="left">Description</ttcol>
<ttcol align="left">Status</ttcol>
<ttcol align="left">Comment</ttcol>
<c>1</c><c>SHA1</c><c>MUST</c><c></c>
<c>2</c><c>SHA2-256</c><c>MUST</c><c></c>
<c>3</c><c>SHA2-384</c><c>MAY</c><c></c>
<c>4</c><c>SHA2-512</c><c>SHOULD</c><c></c>
<c> </c><c>Other hash functions</c><c>MUST NOT</c><c></c>
</texttable>
<t>With the use of Digital Signature, RSASSA-PKCS1-v1.5 MAY be implemented, and RSASSA-PSS MUST be implemented.</t>
<t>RSA keys MUST be greater or equal than 20148 bits.</t>
</section>
</section>
<section anchor="security" title="Security Considerations">
<t> The security of cryptographic-based systems depends on both the strength of the cryptographic algorithms
chosen and the strength of the keys used with those algorithms. The security also depends on the engineering
of the protocol used by the system to ensure that there are no non-cryptographic ways to bypass the security
of the overall system.</t>
<t> The Diffie-Hellman Groups parameter is the most important one to choose conservatively. Any party capturing
all traffic that can break the selected DH group can retroactively gain access to the symmetric keys used
to encrypt all the IPsec data. However, specifying extremely large DH group also puts a considerable load
on the device, especially when this is a large VPN gateway or an IoT constrained device.</t>
<t> This document concerns itself with the selection of cryptographic algorithms for the use of IKEv2,
specifically with the selection of "mandatory-to-implement" algorithms. The algorithms identified in this
document as "MUST implement" or "SHOULD implement" are not known to be broken at the current time, and
cryptographic research so far leads us to believe that they will likely remain secure into the foreseeable
future. However, this isn't necessarily forever and it is expected that new revisions of this
document will be issued from time to time to reflect the current best practice in this area.</t>
</section>
<section anchor="iana" title="IANA Considerations">
<t>This document makes no requests of IANA.</t>
</section>
<section anchor="ack" title="Acknowledgements">
<t> The first version of this document was RFC 4307 by Jeffrey I. Schiller of the Massachusetts Institute of
Technology (MIT). Much of the original text has been copied verbatim.</t>
<t>We would like to thanks Paul Hoffman, Yaron Sheffer and Tommy Pauly for their valuable feed backs.</t>
</section>
</middle>
<!-- ====================================================================== -->
<back>
<references title="Normative References">
&rfc2119;
&rfc4106;
&rfc4307;
&rfc7296;
&rfc5282;
</references>
<references title="Informative References">
<reference anchor="IKEV2-IANA" target="http://www.iana.org/assignments/ikev2-parameters">
<front>
<title>Internet Key Exchange Version 2 (IKEv2) Parameters</title>
<author initials="" surname="" fullname="">
<organization />
</author>
<date />
</front>
</reference>
</references>
<!-- ====================================================================== -->
</back>
</rfc>
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