RFC 8221 PROPOSED STANDARD IPSEC · CRYPTOGRAPHY · ESP · AH
ESP/AH Crypto: Cryptographic Algorithm Implementation Requirements and Usage Guidance for Encapsulating Security Payload (ESP) and Authentication Header (AH)
Implementation requirements and guidance for IPsec ESP and AH cryptographic algorithms.
RFC EDITOR
Wouters, P., Migault, D., Mattsson, J., Nir, Y., and T. Kivinen, "Cryptographic Algorithm Implementation Requirements and Usage Guidance for Encapsulating Security Payload (ESP) and Authentication Header (AH)", RFC 8221, DOI 10.17487/RFC8221, October 2017, <https://www.rfc-editor.org/info/rfc8221>.
BIBTEX
@misc{rfc8221,
series = {Request for Comments},
number = 8221,
howpublished = {RFC 8221},
publisher = {RFC Editor},
doi = {10.17487/RFC8221},
url = {https://www.rfc-editor.org/info/rfc8221},
author = {P. Wouters and D. Migault and J. Mattsson and Y. Nir and T. Kivinen},
title = {{Cryptographic Algorithm Implementation Requirements and Usage Guidance for Encapsulating Security Payload (ESP) and Authentication Header (AH)}},
pagetotal = 15,
year = 2017,
month = oct,
} RFC text
Contents
Internet Engineering Task Force (IETF) P. Wouters
Request for Comments: 8221 Red Hat
Obsoletes: 7321 D. Migault
Category: Standards Track J. Mattsson
ISSN: 2070-1721 Ericsson
Y. Nir
Check Point
T. Kivinen
October 2017
Cryptographic Algorithm Implementation Requirements and Usage Guidance
for Encapsulating Security Payload (ESP) and Authentication Header (AH)
Abstract
This document replaces RFC 7321, "Cryptographic Algorithm
Implementation Requirements and Usage Guidance for Encapsulating
Security Payload (ESP) and Authentication Header (AH)". The goal of
this document is to enable ESP and AH to benefit from cryptography
that is up to date while making IPsec interoperable.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8221.
Copyright Notice
Copyright (c) 2017 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
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Updating Algorithm Implementation Requirements and Usage
Guidance . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Updating Algorithm Requirement Levels . . . . . . . . . . 3
1.3. Document Audience . . . . . . . . . . . . . . . . . . . . 4
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5
3. Manual Keying . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Encryption Must Be Authenticated . . . . . . . . . . . . . . 6
5. ESP Encryption Algorithms . . . . . . . . . . . . . . . . . . 7
6. ESP and AH Authentication Algorithms . . . . . . . . . . . . 9
7. ESP and AH Compression Algorithms . . . . . . . . . . . . . . 10
8. Summary of Changes from RFC 7321 . . . . . . . . . . . . . . 11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
10. Security Considerations . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
11.1. Normative References . . . . . . . . . . . . . . . . . . 12
11.2. Informative References . . . . . . . . . . . . . . . . . 12
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
The Encapsulating Security Payload (ESP) [RFC4303] and the
Authentication Header (AH) [RFC4302] are the mechanisms for applying
cryptographic protection to data being sent over an IPsec Security
Association (SA) [RFC4301].
This document provides guidance and recommendations so that ESP and
AH can be used with cryptographic algorithms that are up to date.
The challenge of such documents is making sure that, over time, IPsec
implementations can use secure and up-to-date cryptographic
algorithms while keeping IPsec interoperable.
1.1. Updating Algorithm Implementation Requirements and Usage Guidance
The field of cryptography evolves continuously: new, stronger
algorithms appear, and existing algorithms are found to be less
secure than 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 compromise.
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 Internet of Things (IoT)
devices.
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 Internet Key Exchange Protocol Version 2 (IKEv2)
specification [RFC7296] and placed in a separate document.
1.2. Updating Algorithm Requirement Levels
The mandatory-to-implement algorithm of tomorrow should already be
available in most implementations of AH/ESP by the time it is made
mandatory. This document attempts to identify and introduce those
algorithms for future mandatory-to-implement status. There is no
guarantee that the algorithms in use today may become mandatory in
the future. Published algorithms are continuously subjected to
cryptographic attack and may become too weak or could become
completely broken before this document is updated.
This document only provides recommendations for the mandatory-to-
implement algorithms and "too weak" algorithms that are recommended
not to be implemented. As a result, any algorithm listed at the
IPsec IANA registry that is not mentioned in this document MAY be
implemented. It is expected that this document will be updated over
time and future versions will only mention algorithms that have
evolved in status. For clarification, when an algorithm has been
mentioned in [RFC7321], this document states explicitly the update of
the status.
Although this document updates the algorithms to keep the AH/ESP
communication secure over time, it also aims at providing
recommendations so that AH/ESP implementations remain interoperable.
AH/ESP interoperability is addressed by an incremental introduction
or deprecation of algorithms. In addition, this document also
considers the new use cases for AH/ESP deployment, such as IoT.
It is expected that deprecation of an algorithm be 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 (see
Section 2). Similarly, an algorithm that has not been mentioned as
mandatory-to-implement is expected to be introduced with a SHOULD
instead of a MUST.
The current trend toward IoT and its adoption of AH/ESP requires this
specific use case to be taken into account as well. IoT devices are
resource-constrained devices, and their choice of algorithms is
motivated by minimizing the footprint 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. Requirement levels that are marked as "IoT" apply
to IoT devices and to server-side implementations that might
presumably need to interoperate with them, including any general-
purpose VPN gateways.
1.3. Document Audience
The recommendations of this document mostly target AH/ESP
implementers as implementations need to meet both high security
expectations as well as high interoperability between various vendors
and with different versions. Interoperability requires a smooth move
to more secure cipher suites. This may differ from a user point of
view that may deploy and configure AH/ESP with only the safest cipher
suite.
This document does not give any recommendations for the use of
algorithms, it only gives recommendations for implementations. The
use of algorithms by a specific user is dictated by their own
security policy requirements, which are outside the scope of this
document.
The algorithms considered here are listed by IANA as part of the
IKEv2 parameters. IKEv1 is out of scope of this document. IKEv1 is
deprecated; the recommendations of this document must not be
considered for IKEv1, nor may IKEv1 parameters be considered by this
document.
The IANA registry for "Internet Key Exchange Version 2 (IKEv2)
Parameters" contains some entries that are not for use with ESP or
AH. This document does not modify the status of those algorithms.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
We define some additional terms here:
SHOULD+ 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.
SHOULD- 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.
MUST- 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-
level.
IoT The Internet of Things.
3. Manual Keying
Manual keying SHOULD NOT be used, as it is inherently dangerous.
Without any secure keying protocol, such as IKE, IPsec does not offer
Perfect Forward Secrecy (PFS) protection; there is no entity to
ensure the refreshing of session keys, the tracking of Security
Parameter Index (SPI) uniqueness, and the single use of nonces,
Initialization Vectors (IVs), and counters. This document was
written for deploying ESP/AH using IKE [RFC7296] and assumes that
keying happens using IKEv2 or higher.
If manual keying is used regardless, Counter Mode algorithms such as
ENCR_AES_CTR, ENCR_AES_CCM, ENCR_AES_GCM, and ENCR_CHACHA20_POLY1305
MUST NOT be used, as it is incompatible with a secure and persistent
handling of the counter (as explained in the Security Considerations
section of [RFC3686]). This particularly applies to IoT devices that
have no state across reboots. At the time of writing, ENCR_AES_CBC
is the only mandatory-to-implement encryption algorithm suitable for
manual keying.
4. Encryption Must Be Authenticated
Encryption without authentication is not effective and MUST NOT be
used. IPsec offers three ways to provide both encryption and
authentication:
o ESP with an Authenticated Encryption with Associated Data (AEAD)
cipher
o ESP with a non-AEAD cipher + authentication
o ESP with a non-AEAD cipher + AH with authentication
The fastest and most modern method is to use ESP with a combined mode
cipher, such as an AEAD cipher, that handles encryption/decryption
and authentication in a single step. In this case, the AEAD cipher
is set as the encryption algorithm, and the authentication algorithm
is set to none. Examples of this are ENCR_AES_GCM_16 and
ENCR_CHACHA20_POLY1305.
A more traditional approach is to use ESP with an encryption and an
authentication algorithm. This approach is slower, as the data has
to be processed twice: once for encryption/decryption and once for
authentication. An example of this is ENCR_AES_CBC combined with
AUTH_HMAC_SHA2_512_256.
The last method that can be used is ESP+AH. This method is NOT
RECOMMENDED. It is the slowest method and also takes up more octets
due to the double header of ESP+AH. This results in a smaller
effective MTU for the encrypted data. With this method, ESP is only
used for confidentiality without an authentication algorithm, and a
second IPsec protocol of type AH is used for authentication. An
example of this is ESP with ENCR_AES_CBC with AH with
AUTH_HMAC_SHA2_512_256.
5. ESP Encryption Algorithms
+-------------------------+------------+---------+----------------+
| Name | Status | AEAD | Comment |
+-------------------------+------------+---------+----------------+
| ENCR_DES_IV64 | MUST NOT | No | UNSPECIFIED |
| ENCR_DES | MUST NOT | No | [RFC2405] |
| ENCR_3DES | SHOULD NOT | No | [RFC2451] |
| ENCR_BLOWFISH | MUST NOT | No | [RFC2451] |
| ENCR_3IDEA | MUST NOT | No | UNSPECIFIED |
| ENCR_DES_IV32 | MUST NOT | No | UNSPECIFIED |
| ENCR_NULL | MUST | No | [RFC2410] |
| ENCR_AES_CBC | MUST | No | [RFC3602][1] |
| ENCR_AES_CCM_8 | SHOULD | Yes | [RFC4309](IoT) |
| ENCR_AES_GCM_16 | MUST | Yes | [RFC4106][1] |
| ENCR_CHACHA20_POLY1305 | SHOULD | Yes | [RFC7634] |
+-------------------------+------------+---------+----------------+
[1] - This requirement level is for 128-bit and 256-bit keys. 192-bit
keys remain at the MAY level.
(IoT) - This requirement is for interoperability with IoT. Only
128-bit keys are at the given level.
IPsec sessions may have very long lifetime and carry multiple
packets, so there is a need to move to 256-bit keys in the long term.
For that purpose, the requirement level for 128-bit keys and 256-bit
keys is MUST (when applicable). In that sense, the status for
256-bit keys has been raised from MAY in [RFC7321] to MUST.
IANA has allocated codes for cryptographic algorithms that have not
been specified by the IETF. Such algorithms are noted as
UNSPECIFIED. Usually, the use of these algorithms is limited to
specific cases, and the absence of specification makes
interoperability difficult for IPsec communications. These
algorithms were not mentioned in [RFC7321], and this document
clarifies that such algorithms MUST NOT be implemented for IPsec
communications.
Similarly, IANA also allocated code points for algorithms that are
not expected to be used to secure IPsec communications. Such
algorithms are noted as non-IPsec. As a result, these algorithms
MUST NOT be implemented.
Various ciphers that are older, not well tested, and never widely
implemented have been changed to MUST NOT.
ENCR_3DES status has been downgraded from MAY in [RFC7321] to SHOULD
NOT. ENCR_CHACHA20_POLY1305 is a more modern approach and
alternative for ENCR_3DES than ENCR_AES_CBC, and so it is expected to
be favored to replace ENCR_3DES.
ENCR_BLOWFISH has been downgraded to MUST NOT as it has been
deprecated for years by TWOFISH, which is not standardized for ESP
and therefore not listed in this document. Some implementations
support TWOFISH using a private range number.
ENCR_NULL status was set to MUST in [RFC7321] and remains a MUST to
enable the use of ESP with only authentication, which is preferred
over AH due to NAT traversal. ENCR_NULL is expected to remain MUST
by protocol requirements.
ENCR_AES_CBC status remains at MUST. ENCR_AES_CBC MUST be
implemented in order to enable interoperability between
implementations that followed [RFC7321]. However, there is a trend
for the industry to move to AEAD encryption, and the overhead of
ENCR_AES_CBC remains quite large, so it is expected to be replaced by
AEAD algorithms in the long term.
ENCR_AES_CCM_8 status was set to MAY in [RFC7321] and has been raised
from MAY to SHOULD in order to interact with IoT devices. As this
case is not a general use case for VPNs, its status is expected to
remain as SHOULD.
ENCR_AES_GCM_16 status has been updated from SHOULD+ to MUST in order
to favor the use of authenticated encryption and AEAD algorithms.
ENCR_AES_GCM_16 has been widely implemented for ESP due to its
increased performance and key longevity compared to ENCR_AES_CBC.
ENCR_CHACHA20_POLY1305 was not ready to be considered at the time of
[RFC7321]. It has been recommended by the Crypto Forum Research
Group (CFRG) and others as an alternative to AES-CBC and AES-GCM. At
the time of writing, there are not enough ESP implementations of
ENCR_CHACHA20_POLY1305 to be able to introduce it at the SHOULD+
level. Its status has been set to SHOULD and is expected to become
MUST in the long term.
6. ESP and AH Authentication Algorithms
Authentication algorithm recommendations in this section are
targeting two types of communications:
o Authenticated-only communications without encryption, such as ESP
with NULL encryption or AH communications.
o Communications that are encrypted with a non-AEAD algorithm that
MUST be combined with an authentication algorithm.
+------------------------+----------------+-------------------------+
| Name | Status | Comment |
+------------------------+----------------+-------------------------+
| AUTH_NONE | MUST / | [RFC7296][RFC5282] |
| | MUST NOT | AEAD-only |
| AUTH_HMAC_MD5_96 | MUST NOT | [RFC2403][RFC7296] |
| AUTH_HMAC_SHA1_96 | MUST- | [RFC2404][RFC7296] |
| AUTH_DES_MAC | MUST NOT | UNSPECIFIED |
| AUTH_KPDK_MD5 | MUST NOT | UNSPECIFIED |
| AUTH_AES_XCBC_96 | SHOULD / MAY | [RFC3566][RFC7296] |
| | | (IoT) |
| AUTH_AES_128_GMAC | MAY | [RFC4543] |
| AUTH_AES_256_GMAC | MAY | [RFC4543] |
| AUTH_HMAC_SHA2_256_128 | MUST | [RFC4868] |
| AUTH_HMAC_SHA2_512_256 | SHOULD | [RFC4868] |
+------------------------+----------------+-------------------------+
(IoT) - This requirement is for interoperability with IoT.
AUTH_NONE has been downgraded from MAY in [RFC7321] to MUST NOT. The
only case where AUTH_NONE is acceptable is when authenticated
encryption algorithms are selected from Section 5. In all other
cases, AUTH_NONE MUST NOT be selected. As ESP and AH both provide
authentication, one may be tempted to combine these protocols to
provide authentication. As mentioned by [RFC7321], it is NOT
RECOMMENDED to use ESP with NULL authentication (with non-
authenticated encryption) in conjunction with AH; some configurations
of this combination of services have been shown to be insecure
[PD10]. In addition, AUTH_NONE authentication cannot be combined
with ESP NULL encryption.
AUTH_HMAC_MD5_96 and AUTH_KPDK_MD5 were not mentioned in [RFC7321].
As MD5 is known to be vulnerable to collisions, these algorithms MUST
NOT be used.
AUTH_HMAC_SHA1_96 has been downgraded from MUST in [RFC7321] to MUST-
as there is an industry-wide trend to deprecate its usage.
AUTH_DES_MAC was not mentioned in [RFC7321]. As DES is known to be
vulnerable, it MUST NOT be used.
AUTH_AES_XCBC_96 is set as SHOULD only in the scope of IoT, as IoT
deployments tend to prefer AES-based Hashed Message Authentication
Code (HMAC) 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 to MAY.
AUTH_AES_128_GMAC status has been downgraded from SHOULD+ to MAY.
Along with AUTH_AES_192_GMAC and AUTH_AES_256_GMAC, these algorithms
should only be used for AH and not for ESP. If using ENCR_NULL,
AUTH_HMAC_SHA2_256_128 is recommended for integrity. If using AES-
GMAC in ESP without authentication, ENCR_NULL_AUTH_AES_GMAC is
recommended. Therefore, these algorithms are kept at MAY.
AUTH_HMAC_SHA2_256_128 was not mentioned in [RFC7321], as no
SHA2-based authentication was mentioned. AUTH_HMAC_SHA2_256_128 MUST
be implemented in order to replace AUTH_HMAC_SHA1_96. Note that due
to a long standing common implementation bug of this algorithm that
truncates the hash at 96 bits instead of 128 bits, it is recommended
that implementations prefer AUTH_HMAC_SHA2_512_256 over
AUTH_HMAC_SHA2_256_128 if they implement AUTH_HMAC_SHA2_512_256.
AUTH_HMAC_SHA2_512_256 SHOULD be implemented 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
additional overhead of AUTH_HMAC_SHA2_512 is negligible.
7. ESP and AH Compression Algorithms
+----------------+----------+-------------+
| Name | Status | Comment |
+----------------+----------+-------------+
| IPCOMP_OUI | MUST NOT | UNSPECIFIED |
| IPCOMP_DEFLATE | MAY | [RFC3173] |
| IPCOMP_LZS | MAY | [RFC2395] |
| IPCOMP_LZJH | MAY | [RFC3051] |
+----------------+----------+-------------+
Compression was not mentioned in [RFC7321]. As it is not widely
deployed, it remains optional and at the MAY level.
8. Summary of Changes from RFC 7321
The following table summarizes the changes from RFC 7321.
+-------------------+----------+-----------------+
| Algorithm | RFC 7321 | RFC 8221 |
+-------------------+----------+-----------------+
| ENCR_AES_GCM_16 | SHOULD+ | MUST |
| ENCR_AES_CCM_8 | MAY | SHOULD |
| ENCR_AES_CTR | MAY | MAY(*) |
| ENCR_3DES | MAY | SHOULD NOT |
| AUTH_HMAC_SHA1_96 | MUST | MUST- |
| AUTH_AES_128_GMAC | SHOULD+ | MAY |
| AUTH_NONE | MAY | MUST / MUST NOT |
+-------------------+----------+-----------------+
(*) This algorithm is not mentioned in the above sections, so it
defaults to MAY.
9. IANA Considerations
This document does not require any IANA actions.
10. Security Considerations
The security of a system that uses cryptography 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 and administration of the protocol used by the system
to ensure that there are no non-cryptographic ways to bypass the
security of the overall system.
This document concerns itself with the selection of cryptographic
algorithms for the use of ESP and AH, 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 to date
leads us to believe that they will likely remain secure into the
foreseeable future. However, this is not necessarily forever.
Therefore, we expect that revisions of that document will be issued
from time to time to reflect the current best practice in this area.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[RFC7321] McGrew, D. and P. Hoffman, "Cryptographic Algorithm
Implementation Requirements and Usage Guidance for
Encapsulating Security Payload (ESP) and Authentication
Header (AH)", RFC 7321, DOI 10.17487/RFC7321, August 2014,
<https://www.rfc-editor.org/info/rfc7321>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
11.2. Informative References
[PD10] Paterson, K. and J. Degabriele, "On the (in)security of
IPsec in MAC-then-encrypt configurations", Proceedings of
the 17th ACM Conference on Computer and Communications
Security (ACM CCS), DOI 10.1145/1866307.1866363, 2010.
[RFC2395] Friend, R. and R. Monsour, "IP Payload Compression Using
LZS", RFC 2395, DOI 10.17487/RFC2395, December 1998,
<https://www.rfc-editor.org/info/rfc2395>.
[RFC2403] Madson, C. and R. Glenn, "The Use of HMAC-MD5-96 within
ESP and AH", RFC 2403, DOI 10.17487/RFC2403, November
1998, <https://www.rfc-editor.org/info/rfc2403>.
[RFC2404] Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96 within
ESP and AH", RFC 2404, DOI 10.17487/RFC2404, November
1998, <https://www.rfc-editor.org/info/rfc2404>.
[RFC2405] Madson, C. and N. Doraswamy, "The ESP DES-CBC Cipher
Algorithm With Explicit IV", RFC 2405,
DOI 10.17487/RFC2405, November 1998,
<https://www.rfc-editor.org/info/rfc2405>.
[RFC2410] Glenn, R. and S. Kent, "The NULL Encryption Algorithm and
Its Use With IPsec", RFC 2410, DOI 10.17487/RFC2410,
November 1998, <https://www.rfc-editor.org/info/rfc2410>.
[RFC2451] Pereira, R. and R. Adams, "The ESP CBC-Mode Cipher
Algorithms", RFC 2451, DOI 10.17487/RFC2451, November
1998, <https://www.rfc-editor.org/info/rfc2451>.
[RFC3051] Heath, J. and J. Border, "IP Payload Compression Using
ITU-T V.44 Packet Method", RFC 3051, DOI 10.17487/RFC3051,
January 2001, <https://www.rfc-editor.org/info/rfc3051>.
[RFC3173] Shacham, A., Monsour, B., Pereira, R., and M. Thomas, "IP
Payload Compression Protocol (IPComp)", RFC 3173,
DOI 10.17487/RFC3173, September 2001,
<https://www.rfc-editor.org/info/rfc3173>.
[RFC3566] Frankel, S. and H. Herbert, "The AES-XCBC-MAC-96 Algorithm
and Its Use With IPsec", RFC 3566, DOI 10.17487/RFC3566,
September 2003, <https://www.rfc-editor.org/info/rfc3566>.
[RFC3602] Frankel, S., Glenn, R., and S. Kelly, "The AES-CBC Cipher
Algorithm and Its Use with IPsec", RFC 3602,
DOI 10.17487/RFC3602, September 2003,
<https://www.rfc-editor.org/info/rfc3602>.
[RFC3686] Housley, R., "Using Advanced Encryption Standard (AES)
Counter Mode With IPsec Encapsulating Security Payload
(ESP)", RFC 3686, DOI 10.17487/RFC3686, January 2004,
<https://www.rfc-editor.org/info/rfc3686>.
[RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode
(GCM) in IPsec Encapsulating Security Payload (ESP)",
RFC 4106, DOI 10.17487/RFC4106, June 2005,
<https://www.rfc-editor.org/info/rfc4106>.
[RFC4309] Housley, R., "Using Advanced Encryption Standard (AES) CCM
Mode with IPsec Encapsulating Security Payload (ESP)",
RFC 4309, DOI 10.17487/RFC4309, December 2005,
<https://www.rfc-editor.org/info/rfc4309>.
[RFC4543] McGrew, D. and J. Viega, "The Use of Galois Message
Authentication Code (GMAC) in IPsec ESP and AH", RFC 4543,
DOI 10.17487/RFC4543, May 2006,
<https://www.rfc-editor.org/info/rfc4543>.
[RFC4868] Kelly, S. and S. Frankel, "Using HMAC-SHA-256, HMAC-SHA-
384, and HMAC-SHA-512 with IPsec", RFC 4868,
DOI 10.17487/RFC4868, May 2007,
<https://www.rfc-editor.org/info/rfc4868>.
[RFC5282] Black, D. and D. McGrew, "Using Authenticated Encryption
Algorithms with the Encrypted Payload of the Internet Key
Exchange version 2 (IKEv2) Protocol", RFC 5282,
DOI 10.17487/RFC5282, August 2008,
<https://www.rfc-editor.org/info/rfc5282>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>.
[RFC7634] Nir, Y., "ChaCha20, Poly1305, and Their Use in the
Internet Key Exchange Protocol (IKE) and IPsec", RFC 7634,
DOI 10.17487/RFC7634, August 2015,
<https://www.rfc-editor.org/info/rfc7634>.
Acknowledgements
Some of the wording in this document was adapted from [RFC7321], the
document that this one obsoletes, which was written by D. McGrew and
P. Hoffman.
Authors' Addresses
Paul Wouters
Red Hat
Email: pwouters@redhat.com
Daniel Migault
Ericsson
8275 Trans Canada Route
Saint-Laurent, QC H4S 0B6
Canada
Phone: +1 514-452-2160
Email: daniel.migault@ericsson.com
John Mattsson
Ericsson AB
SE-164 80 Stockholm
Sweden
Email: john.mattsson@ericsson.com
Yoav Nir
Check Point Software Technologies Ltd.
5 Hasolelim St.
Tel Aviv 6789735
Israel
Email: ynir.ietf@gmail.com
Tero Kivinen
Email: kivinen@iki.fi
ISO Plain Language
On this page
PROBLEMIPsec implementations need algorithms that are secure enough for current use while retaining interoperability across devices and versions.
MECHANISMThe RFC assigns implementation requirement levels to encryption, authentication, and compression algorithms, and recommends authenticated encryption where available.
STATUS TODAYRFC 8221 obsoletes RFC 7321 and is updated by RFC 9395, so its requirement levels may have later changes.
§1Purpose and Audience
Encapsulating Security Payload (ESP) and Authentication Header (AH) protect data sent over an IPsec Security Association. RFC 8221 updates the algorithm implementation requirements so implementations can adopt current cryptography and remain interoperable.
The recommendations target implementers, not users configuring their own security policy. The document covers IKEv2 parameters; IKEv1 is outside its scope.
This RFC tells implementers which algorithms their ESP and AH software should support. It does not tell users which algorithms to select for their own connections.
§2Requirement Levels and Gradual Change
The RFC uses the BCP 14 requirement words and defines SHOULD+, SHOULD-, and MUST-. SHOULD+ is likely to become MUST; SHOULD- may move down to MAY; and MUST- is expected to stop being a MUST in a future document.
Algorithm levels are intended to change gradually so implementations can update while staying interoperable. An IoT label identifies levels intended for interoperability with resource-constrained devices and servers that communicate with them.
Requirement levels show what an implementation needs to support now and may need to support later. The extra plus and minus forms signal expected future changes.
§3Manual Keys and Authenticated Encryption
The RFC says manual keying SHOULD NOT be used. Without a keying protocol such as IKE, IPsec cannot refresh session keys or reliably manage unique identifiers, nonces, initialization vectors, and counters.
Encryption without authentication MUST NOT be used. ESP can combine both services in an AEAD algorithm, use a separate authentication algorithm with non-AEAD encryption, or combine ESP with AH; the RFC does not recommend the last option because of speed and header overhead.
Manual keys leave important key-management work to administrators and are discouraged. Encrypted traffic also needs authentication so receivers can detect changes.
§5ESP Encryption Algorithm Levels
ENCR_NULL, ENCR_AES_CBC, and ENCR_AES_GCM_16 are MUST. ENCR_AES_CCM_8 and ENCR_CHACHA20_POLY1305 are SHOULD; ENCR_3DES is SHOULD NOT; and several older or unspecified algorithms are MUST NOT.
The MUST level for AES applies to 128-bit and 256-bit keys; 192-bit keys remain MAY. The RFC explains that ENCR_AES_GCM_16 was raised to MUST to favor authenticated encryption, while ENCR_AES_CBC remains required for interoperability.
The RFC gives each encryption method a support level. It requires implementations to support AES-GCM-16 and AES-CBC, while it discourages or forbids several older choices.
- MUSTENCR_NULL, ENCR_AES_CBC, ENCR_AES_GCM_16 — Implementations must support these methods.
- SHOULDENCR_AES_CCM_8, ENCR_CHACHA20_POLY1305 — Implementations should support these methods.
- SHOULD NOTENCR_3DES — Implementations should avoid this method.
- MUST NOTENCR_DES, ENCR_BLOWFISH, ENCR_3IDEA and related older methods — Implementations must not support these methods for IPsec.
§6Authentication and Compression Levels
AUTH_HMAC_SHA2_256_128 is MUST, AUTH_HMAC_SHA1_96 is MUST-, and AUTH_HMAC_SHA2_512_256 is SHOULD. AUTH_NONE is allowed only with authenticated encryption; otherwise it is MUST NOT. Several older authentication methods are also MUST NOT.
Compression remains optional: DEFLATE, LZS, and LZJH are MAY, while IPCOMP_OUI is MUST NOT. The RFC explains these levels as implementation requirements, not user configuration requirements.
Implementations must support a SHA-2 authentication method and should support another SHA-2 method. Compression remains optional under this RFC.
§8Changes from RFC 7321
RFC 8221 moves the requirements toward authenticated encryption and away from SHA-1 and 3DES. AES-GCM-16 moves to MUST, AES-CCM-8 moves to SHOULD, and 3DES moves to SHOULD NOT.
The RFC also changes the requirement levels for authentication algorithms, including AUTH_HMAC_SHA1_96 moving from MUST to MUST-. These changes replace RFC 7321's earlier guidance.
This revision raises some newer algorithms and lowers the levels for older ones. RFC 9395 later updates this document, so its changes may affect these levels.
§10Security Considerations
System security depends on algorithms and keys as well as the engineering and administration around them. The RFC says algorithms marked MUST or SHOULD were not known to be broken when it was written, but this may not remain true indefinitely.
The document expects future revisions as cryptographic knowledge changes. It requires no IANA actions.
Algorithm recommendations can become outdated as research changes. The RFC expects future revisions and notes that secure operation also depends on keys and system administration.
§8References
[RFC4301]RFC 4301Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, December 2005.December 2005[RFC4302]RFC 4302Kent, S., "IP Authentication Header", RFC 4302, December 2005.December 2005[RFC4303]RFC 4303Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, December 2005.December 2005[RFC7321]RFC 7321McGrew, D. and P. Hoffman, "Cryptographic Algorithm Implementation Requirements and Usage Guidance for Encapsulating Security Payload (ESP) and Authentication Header (AH)", RFC 7321, August 2014.August 2014[RFC7296]RFC 7296Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. Kivinen, "Internet Key Exchange Protocol Version 2 (IKEv2)", STD 79, RFC 7296, October 2014.October 2014