Internet Engineering Task Force M. Baushke
Internet-Draft Juniper Networks, Inc.
Updates: 4250 (if approved) January 2, 2018
Intended status: Standards Track
Expires: July 6, 2018
Key Exchange (KEX) Method Updates and Recommendations for Secure Shell
(SSH)
draft-ietf-curdle-ssh-kex-sha2-10
Abstract
This document is intended to update the recommended set of key
exchange methods for use in the Secure Shell (SSH) protocol to meet
evolving needs for stronger security. This document updates RFC
4250.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 6, 2018.
Copyright Notice
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document authors. All rights reserved.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Overview and Rationale . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Key Exchange Methods . . . . . . . . . . . . . . . . . . . . 3
3.1. curve25519-sha256 . . . . . . . . . . . . . . . . . . . . 4
3.2. curve448-sha512 . . . . . . . . . . . . . . . . . . . . . 4
3.3. diffie-hellman-group-exchange-sha1 . . . . . . . . . . . 4
3.4. diffie-hellman-group-exchange-sha256 . . . . . . . . . . 4
3.5. diffie-hellman-group1-sha1 . . . . . . . . . . . . . . . 4
3.6. diffie-hellman-group14-sha1 . . . . . . . . . . . . . . . 5
3.7. diffie-hellman-group14-sha256 . . . . . . . . . . . . . . 5
3.8. diffie-hellman-group15-sha512 . . . . . . . . . . . . . . 5
3.9. diffie-hellman-group16-sha512 . . . . . . . . . . . . . . 5
3.10. diffie-hellman-group17-sha512 . . . . . . . . . . . . . . 5
3.11. diffie-hellman-group18-sha512 . . . . . . . . . . . . . . 6
3.12. ecdh-sha2-nistp256 . . . . . . . . . . . . . . . . . . . 6
3.13. ecdh-sha2-nistp384 . . . . . . . . . . . . . . . . . . . 6
3.14. ecdh-sha2-nistp521 . . . . . . . . . . . . . . . . . . . 6
3.15. gss-gex-sha1-* . . . . . . . . . . . . . . . . . . . . . 7
3.16. gss-group1-sha1-* . . . . . . . . . . . . . . . . . . . . 7
3.17. gss-group14-sha1-* . . . . . . . . . . . . . . . . . . . 7
3.18. gss-group14-sha256-* . . . . . . . . . . . . . . . . . . 7
3.19. gss-group15-sha512-* . . . . . . . . . . . . . . . . . . 8
3.20. gss-group16-sha512-* . . . . . . . . . . . . . . . . . . 8
3.21. gss-group17-sha512-* . . . . . . . . . . . . . . . . . . 8
3.22. gss-group18-sha512-* . . . . . . . . . . . . . . . . . . 8
3.23. gss-nistp256-sha256-* . . . . . . . . . . . . . . . . . . 8
3.24. gss-nistp384-sha384-* . . . . . . . . . . . . . . . . . . 8
3.25. gss-nistp521-sha512-* . . . . . . . . . . . . . . . . . . 9
3.26. gss-curve25519-sha256-* . . . . . . . . . . . . . . . . . 9
3.27. gss-curve448-sha512-* . . . . . . . . . . . . . . . . . . 9
3.28. rsa1024-sha1 . . . . . . . . . . . . . . . . . . . . . . 9
3.29. rsa2048-sha256 . . . . . . . . . . . . . . . . . . . . . 9
4. Selecting an appropriate hashing algorithm . . . . . . . . . 9
5. Summary Guidance for Key Exchange Method Names . . . . . . . 10
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Overview and Rationale
Secure Shell (SSH) is a common protocol for secure communication on
the Internet. In [RFC4253], SSH originally defined two Key Exchange
Method Names that MUST be implemented. Over time, what was once
considered secure, is no longer considered secure. The purpose of
this RFC is to recommend that some published key exchanges be
deprecated as well as recommending some that SHOULD and one that MUST
be adopted. This document updates [RFC4250].
This document adds recommendations for adoption of Key Exchange
Methods which MUST, SHOULD, MAY, SHOULD NOT, and MUST NOT be
implemented. New key exchange methods will use the SHA-2 family of
hashes found in [RFC6234] and are drawn from these ssh-curves from
[I-D.ietf-curdle-ssh-curves] and DH MODP primes from the [RFC8268]
and gss-keyex [I-D.ietf-curdle-gss-keyex-sha2].
2. Requirements Language
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 [RFC2119].
3. Key Exchange Methods
This memo adopts the style and conventions of [RFC4253] in specifying
how the use of data key exchange is indicated in SSH.
This RFC also collects Key Exchange Method Names in various existing
RFCs [RFC4253], [RFC4419], [RFC4432], [RFC4462], [RFC5656],
[RFC8268], [I-D.ietf-curdle-gss-keyex-sha2], and
[I-D.ietf-curdle-ssh-curves] and provides a suggested suitability for
implementation of MUST, SHOULD, SHOULD NOT, and MUST NOT. Any method
not explicitly listed, MAY be implemented.
This document is intended to provide guidance as to what Key Exchange
Algorithms are to be considered for new or updated SSH
implementations. This document will be superseded when one or more
of the listed algorithms are considered too weak to continue to use
securely, in which case they will likely be downgraded to SHOULD NOT
or MUST NOT. Or, when newer methods have been analyzed and found to
be secure with wide enough adoption to upgrade their recommendation
from MAY to SHOULD or MUST.
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3.1. curve25519-sha256
The Curve25519 provides strong security and is efficient on a wide
range of architectures with properties that allow better
implementation properties compared to traditional elliptic curves.
The use of SHA2-256 (also known as SHA-256) as defined in [RFC6234]
for integrity is a reasonable one for this method. This Key Exchange
Method is described in [I-D.ietf-curdle-ssh-curves] and is similar to
the IKEv2 Key Agreement described in [RFC8031]. This Key Exchange
Method has multiple implementations and SHOULD be implemented in any
SSH interested in using elliptic curve based key exchanges.
3.2. curve448-sha512
The Curve448 provides very strong security. It uses SHA2-512 (also
known as SHA-256) defined in [RFC6234] for integrity. It is probably
stronger and more work than is currently needed. This Key Exchange
Method is described in [I-D.ietf-curdle-ssh-curves] and is similar to
the IKEv2 Key Agreement described in [RFC8031]. This method MAY be
implemented.
3.3. diffie-hellman-group-exchange-sha1
This set of ephemerally generated key exchange groups uses SHA-1 as
defined in [RFC4419]. However, SHA-1 has security concerns provided
in [RFC6194], so it would be better to use a key exchange method
which uses a SHA-2 hash as in [RFC6234] for integrity. This key
exchange SHOULD NOT be used.
3.4. diffie-hellman-group-exchange-sha256
This set of ephemerally generated key exchange groups uses SHA2-256
as defined in [RFC4419]. [RFC8270] mandates implementations avoid
any MODP group with less than 2048 bits. This key exchange MAY be
used.
3.5. diffie-hellman-group1-sha1
This method is decribed in [RFC4253] and uses [RFC7296] Oakley Group
2 (a 1024-bit MODP group) and SHA-1 [RFC3174]. Due to recent
security concerns with SHA-1 [RFC6194] and with MODP groups with less
than 2048 bits (see [LOGJAM] and [NIST-SP-800-131Ar1]), this method
is considered insecure. This method is being moved from MUST to
SHOULD NOT instead of MUST NOT only to allow a transition time to get
off of it. There are many old implementations out there that may
still need to use this key exchange, it should be removed from server
implementations as quickly as possible.
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3.6. diffie-hellman-group14-sha1
This method uses [RFC3526] group14 (a 2048-bit MODP group) which is
still a reasonable size. This key exchange group uses SHA-1 which
has security concerns [RFC6194]. However, this group is still strong
enough and is widely deployed. This method is being moved from MUST
to SHOULD to aid in transition to stronger SHA-2 based hashes. This
method will transition to SHOULD NOT when SHA-2 alternatives are more
generally available.
3.7. diffie-hellman-group14-sha256
This key exchange method is defined in [RFC8268] and uses the group14
(a 2048-bit MODP group) along with a SHA-2 (SHA2-256) hash as in
[RFC6234] for integrity. This represents the smallest Finite Field
Cryptography (FFC) Diffie-Hellman (DH) key exchange method considered
to be secure. It is a reasonably simple transition to move from
SHA-1 to SHA-2. This method MUST be implemented.
3.8. diffie-hellman-group15-sha512
This key exchange method is defined in [RFC8268] and uses group15
along with a SHA-2 (SHA2-512) hash as in [RFC6234] for integrity.
Note: The use of this 3072-bit MODP group would be equally justified
to use SHA2-384 as the hash rather than SHA2-512. However, some
small implementations would rather only worry about two rather than
three new hashing functions. This group does not really provide much
additional head room over the 2048-bit group14 FFC DH and the
predominate open source implementations are not adopting it. This
method MAY be implemented.
3.9. diffie-hellman-group16-sha512
This key exchange method is defined in [RFC8268] and uses group16
along with a SHA-2 (SHA2-512) hash as in [RFC6234] for integrity.
The use of FFC DH is well understood and trusted. Adding larger
modulus sizes and protecting with SHA2-512 should give enough head
room to be ready for the next scare that someone has pre-computed it.
This modulus (4096-bit) is larger than that required by [CNSA-SUITE]
and should be sufficient to inter-operate with more paranoid nation-
states. This method SHOULD be implemented.
3.10. diffie-hellman-group17-sha512
This key exchange method is defined in [RFC8268] and uses group17
along with a SHA-2 (SHA2-512) hash as in [RFC6234] for integrity.
The use of this 6144-bit MODP group is going to be slower than what
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may be desirable. It is provided to help those who wish to avoid
using ECC algorithms. This method MAY be implemented.
3.11. diffie-hellman-group18-sha512
This key exchange method is defined in [RFC8268] and uses group18
along with a SHA-2 (SHA2-512) hash as in [RFC6234] for integrity.
The use of this 8192-bit MODP group is going to be slower than what
may be desirable. It is provided to help those who wish to avoid
using ECC algorithms. This method MAY be implemented.
3.12. ecdh-sha2-nistp256
This key exchange method is defined in [RFC5656]. Elliptic Curve
Diffie-Hellman (ECDH) are often implemented because they are smaller
and faster than using large FFC primes with traditional Diffie-
Hellman (DH). However, given [CNSA-SUITE] and [safe-curves], this
curve may not be as useful and strong as desired for handling TOP
SECRET information for some applications. The SSH development
community is divided on this and many implementations do exist. If
traditional ECDH key exchange methods are implemented, then this
method SHOULD be implemented.
It is advisable to match the ECDSA and ECDH algorithms to use the
same curve for both.
3.13. ecdh-sha2-nistp384
This key exchange method is defined in [RFC5656]. This ECDH method
should be implemented because it is smaller and faster than using
large FFC primes with traditional Diffie-Hellman (DH). Given
[CNSA-SUITE], it is considered good enough for TOP SECRET. If
traditional ECDH key exchange methods are implemented, then this
method SHOULD be implemented.
Research into ways of breaking ECDSA continues. Papers such as
[ECDSA-Nonce-Leak] as well as concerns raised in [safe-curves] may
mean that this algorithm will need to be downgraded in the future
along the other ECDSA nistp curves.
3.14. ecdh-sha2-nistp521
This key exchange method is defined in [RFC5656]. This ECDH method
may be implemented because it is smaller and faster than using large
FFC primes with traditional Diffie-Hellman (DH). It is not listed in
[CNSA-SUITE], so it is not currently appropriate for TOP SECRET. It
is possible that the mismatch between the 521-bit key and the 512-bit
hash could mean that as many as nine bits of this key could be at
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risk of leaking if appropriate padding measures are not taken. This
method MAY be implemented, but is not recommended.
3.15. gss-gex-sha1-*
This key exchange method is defined in [RFC4462]. This set of
ephemerally generated key exchange groups uses SHA-1 which has
security concerns [RFC6194]. It is recommended that these key
exchange groups NOT be used. This key exchange SHOULD NOT be used.
It is intended that it move to MUST NOT as soon as the majority of
server implementations no longer offer it. It should be removed from
server implementations as quickly as possible.
3.16. gss-group1-sha1-*
This key exchange method is defined in [RFC4462]. This method
suffers from the same problems of diffie-hellman-group1-sha1. It
uses [RFC7296] Oakley Group 2 (a 1024-bit MODP group) and SHA-1
[RFC3174]. Due to recent security concerns with SHA-1 [RFC6194] and
with MODP groups with less than 2048 bits (see [LOGJAM] and
[NIST-SP-800-131Ar1]), this method is considered insecure. This
method SHOULD NOT be implemented. It is intended that it move to
MUST NOT as soon as the majority of server implementations no longer
offer it. It should be removed from server implementations as
quickly as possible.
3.17. gss-group14-sha1-*
This key exchange method is defined in [RFC4462]. This generated key
exchange groups uses SHA-1 which has security concerns [RFC6194]. If
GSS-API key exchange methods are being used, then this one SHOULD be
implemented until such time as SHA-2 variants may be implemented and
deployed. This method will transition to SHOULD NOT when SHA-2
alternatives are more generally available. No other standard
indicated that this method was anything other than optional even
though it was implemented in all GSS-API systems. This method MAY be
implemented.
3.18. gss-group14-sha256-*
This key exchange method is defined in
[I-D.ietf-curdle-gss-keyex-sha2]. This key exchange uses the group14
(a 2048-bit MODP group) along with a SHA-2 (SHA2-256) hash. This
represents the smallest Finite Field Cryptography (FFC) Diffie-
Hellman (DH) key exchange method considered to be secure. It is a
reasonably simple transition to move from SHA-1 to SHA-2. If the
GSS-API is to be used, then this method SHOULD be implemented.
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3.19. gss-group15-sha512-*
This key exchange method is defined in
[I-D.ietf-curdle-gss-keyex-sha2]. The use of this 3072-bit MODP
group does not really provide much additional head room over the
2048-bit group14 FFC DH. If the GSS-API is to be used, then this
method MAY be implemented.
3.20. gss-group16-sha512-*
This key exchange method is defined in
[I-D.ietf-curdle-gss-keyex-sha2]. The use of FFC DH is well
understood and trusted. Adding larger modulus sizes and protecting
with SHA2-512 should give enough head room to be ready for the next
scare that someone has pre-computed. This modulus (4096-bit) is
larger than that required by [CNSA-SUITE] and should be sufficient to
inter-operate with more paranoid nation-states. If the GSS-API is to
be used, then this method SHOULD be implemented.
3.21. gss-group17-sha512-*
This key exchange method is defined in
[I-D.ietf-curdle-gss-keyex-sha2]. The use of this 6144-bit MODP
group is going to be slower than what may be desirable. It is
provided to help those who wish to avoid using ECC algorithms. If
the GSS-API is to be used, then this method MAY be implemented.
3.22. gss-group18-sha512-*
This key exchange method is defined in
[I-D.ietf-curdle-gss-keyex-sha2]. The use of this 8192-bit MODP
group is going to be slower than what may be desirable. It is
provided to help those who prefer to avoid using ECC algorithms. If
the GSS-API is to be used, then this method MAY be implemented.
3.23. gss-nistp256-sha256-*
This key exchange method is defined in
[I-D.ietf-curdle-gss-keyex-sha2]. If the GSS-API is to be used with
ECC algorithms, then this method SHOULD be implemented.
3.24. gss-nistp384-sha384-*
This key exchange method is defined in
[I-D.ietf-curdle-gss-keyex-sha2]. If the GSS-API is to be used with
ECC algorithms, then this method SHOULD be implemented to permit TOP
SECRET information to be communicated.
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3.25. gss-nistp521-sha512-*
This key exchange method is defined in
[I-D.ietf-curdle-gss-keyex-sha2]. If the GSS-API is to be used with
ECC algorithms, then this method MAY be implemented.
3.26. gss-curve25519-sha256-*
This key exchange method is defined in
[I-D.ietf-curdle-gss-keyex-sha2]. If the GSS-API is to be used with
ECC algorithms, then this method SHOULD be implemented.
3.27. gss-curve448-sha512-*
This key exchange method is defined in
[I-D.ietf-curdle-gss-keyex-sha2]. If the GSS-API is to be used with
ECC algorithms, then this method MAY be implemented.
3.28. rsa1024-sha1
This key exchange method is defined in [RFC4432]. The security of
RSA 1024-bit modulus keys is not good enough any longer. A key size
should be 2048-bits. This generated key exchange groups uses SHA-1
which has security concerns [RFC6194]. This method MUST NOT be
implemented.
3.29. rsa2048-sha256
This key exchange method is defined in [RFC4432]. An RSA 2048-bit
modulus key with a SHA2-256 hash. At the present time, a 2048-bit
RSA key is considered to be suffiently strong in [NIST-SP-800-131Ar1]
to be permitted. In addition, the use of a SHA-2 hash as defined in
[RFC6234] is a good integrity measure. This method MAY be
implemented.
4. Selecting an appropriate hashing algorithm
As may be seen from the above, the Key Exchange Methods area all
using either SHA256 or SHA512 with the exception of the ecdh-
sha2-nistp384 which uses SHA384.
The cited CNSA Suite specifies the use of SHA384 and says that SHA256
is no longer good enough for TOP SECRET. Nothing is said about the
use of SHA512. It may be that the internal state of 1024 bits in
both SHA384 and SHA512 makes the SHA384 more secure because it does
not leak an additional 128 bits of state. Of course, the use of
SHA384 also reduces the security strength to 384 bits instead of
being 512 bits. This seems to contradict the desire to double the
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symmetric key strength in order to try to be safe from Post Quantum
Computing (PQC) attacks given a session key derived from the key
exchange will be limited to the security strength of the hash being
used.
The move away from SHA256 to SHA512 for the newer key exchange
methods is more to try to slow Grover's algorithm (a PQC attack)
slightly. It is also the case that SHA2-512 may, in many modern
CPUs, be implemented more efficiently using 64-bit arithmetic than
SHA256 which is faster on 32-bit CPUs. The selection of SHA384 vs
SHA512 is more about reducing the number of code point alternatives
to negotiate. There seemed to be consensus in favor of SHA2-512 over
SHA2-384 for key exchanges.
5. Summary Guidance for Key Exchange Method Names
The Implement column is the current recommendations of this RFC. Key
Exchange Method Names are listed alphabetically.
Key Exchange Method Name Reference Implement
---------------------------------- ---------- ----------
curve25519-sha256 ssh-curves SHOULD
diffie-hellman-group-exchange-sha1 RFC4419 SHOULD NOT
diffie-hellman-group1-sha1 RFC4253 SHOULD NOT
diffie-hellman-group14-sha1 RFC4253 SHOULD
diffie-hellman-group14-sha256 RFC8268 MUST
diffie-hellman-group16-sha512 RFC8268 SHOULD
ecdh-sha2-nistp256 RFC5656 SHOULD
ecdh-sha2-nistp384 RFC5656 SHOULD
gss-gex-sha1-* RFC4462 SHOULD NOT
gss-group1-sha1-* RFC4462 SHOULD NOT
gss-group14-sha256-* gss-keyex SHOULD
gss-group16-sha512-* gss-keyex SHOULD
gss-nistp256-sha256-* gss-keyex SHOULD
gss-nistp384-sha384-* gss-keyex SHOULD
gss-curve25519-sha256-* gss-keyex SHOULD
rsa1024-sha1 RFC4432 MUST NOT
The full set of official [IANA-KEX] key algorithm method names not
otherwise mentioned in this document MAY be implemented.
The guidance of this document is that the SHA-1 algorithm hashing
SHOULD NOT be used. If it is used in implementations, it should only
be provided for backwards compatibility, should not be used in new
designs, and should be phased out of existing key exchanges as
quickly as possible because of its known weaknesses. Any key
exchange using SHA-1 should not be in a default key exchange list if
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at all possible. If they are needed for backward compatibility, they
SHOULD be listed after all of the SHA-2 based key exchanges.
The [RFC4253] MUST diffie-hellman-group14-sha1 method SHOULD be
retained for compatibility with older Secure Shell implementations.
It is intended that this key exchange method be phased out as soon as
possible. It SHOULD be listed after all possible SHA-2 based key
exchanges.
It is believed that all current SSH implementations should be able to
achieve an implementation of the "diffie-hellman-group14-sha256"
method. To that end, this is one method that MUST be implemented.
[TO BE REMOVED: This registration should take place at the following
location: <http://www.iana.org/assignments/ssh-parameters/ssh-
parameters.xhtml#ssh-parameters-16>]
6. Acknowledgements
Thanks to the following people for review and comments: Denis Bider,
Peter Gutmann, Damien Miller, Niels Moeller, Matt Johnston, Iwamoto
Kouichi, Simon Josefsson, Dave Dugal, Daniel Migault, Anna Johnston,
and Tero Kivinen.
Thanks to the following people for code to implement inter-operable
exchanges using some of these groups as found in an this draft:
Darren Tucker for OpenSSH and Matt Johnston for Dropbear. And thanks
to Iwamoto Kouichi for information about RLogin, Tera Term (ttssh)
and Poderosa implementations also adopting new Diffie-Hellman groups
based on this draft.
7. Security Considerations
This SSH protocol provides a secure encrypted channel over an
insecure network. It performs server host authentication, key
exchange, encryption, and integrity protection. It also derives a
unique session ID that may be used by higher-level protocols.
Full security considerations for this protocol are provided in
[RFC4251]
It is desirable to deprecate or remove key exchange method name that
are considered weak. A key exchange method may be weak because too
few bits are used, or the hashing algorithm is considered too weak.
The diffie-hellman-group1-sha1 is being moved from MUST to MUST NOT.
This method used [RFC7296] Oakley Group 2 (a 1024-bit MODP group) and
SHA-1 [RFC3174]. Due to recent security concerns with SHA-1
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[RFC6194] and with MODP groups with less than 2048 bits
[NIST-SP-800-131Ar1], this method is no longer considered secure.
The United States Information Assurance Directorate (IAD) at the
National Security Agency (NSA) has published a FAQ
[MFQ-U-OO-815099-15] suggesting that the use of Elliptic Curve
Diffie-Hellman (ECDH) using the nistp256 curve and SHA-2 based hashes
less than SHA2-384 are no longer sufficient for transport of TOP
SECRET information. If your systems need to be concerned with TOP
SECRET information, then the guidance for supporting lesser security
strength key exchanges may be omitted for your implementations.
The MODP group14 is already required for SSH implementations and most
implementations already have a SHA2-256 implementation, so diffie-
hellman-group14-sha256 is provided as an easy to implement and faster
to use key exchange. Small embedded applications may find this KEX
desirable to use.
The NSA Information Assurance Directorate (IAD) has also published
the Commercial National Security Algorithm Suite (CNSA Suite)
[CNSA-SUITE] in which the 3072-bit MODP Group 15 in [RFC3526] is
explicitly mentioned as the minimum modulus to protect TOP SECRET
communications.
It has been observed in [safe-curves] that the NIST Elliptic Curve
Prime Curves (P-256, P-384, and P-521) are perhaps not the best
available for Elliptic Curve Cryptography (ECC) Security. For this
reason, none of the [RFC5656] curves are mandatory to implement.
However, the requirement that "every compliant SSH ECC implementation
MUST implement ECDH key exchange" is now taken to mean that if ecdsa-
sha2-[identifier] is implemented, then ecdh-sha2-[identifier] MUST be
implemented.
In a Post-Quantum Computing (PQC) world, it will be desirable to use
larger cyclic subgroups. To do this using Elliptic Curve
Cryptography will require much larger prime base fields, greatly
reducing their efficiency. Finite Field based Cryptography already
requires large enough base fields to accommodate larger cyclic
subgroups. Until such time as a PQC method of key exchange is
developed and adopted, it may be desirable to generate new and larger
DH groups to avoid pre-calculation attacks that are provably not
backdoored.
8. IANA Considerations
IANA is requested to annotate entries in [IANA-KEX] which MUST NOT be
implemented as being deprecated by this document.
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9. References
9.1. 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>.
[RFC3526] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP)
Diffie-Hellman groups for Internet Key Exchange (IKE)",
RFC 3526, DOI 10.17487/RFC3526, May 2003,
<https://www.rfc-editor.org/info/rfc3526>.
[RFC4250] Lehtinen, S. and C. Lonvick, Ed., "The Secure Shell (SSH)
Protocol Assigned Numbers", RFC 4250,
DOI 10.17487/RFC4250, January 2006,
<https://www.rfc-editor.org/info/rfc4250>.
[RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
January 2006, <https://www.rfc-editor.org/info/rfc4253>.
[RFC8031] Nir, Y. and S. Josefsson, "Curve25519 and Curve448 for the
Internet Key Exchange Protocol Version 2 (IKEv2) Key
Agreement", RFC 8031, DOI 10.17487/RFC8031, December 2016,
<https://www.rfc-editor.org/info/rfc8031>.
[RFC8268] Baushke, M., "More Modular Exponentiation (MODP) Diffie-
Hellman (DH) Key Exchange (KEX) Groups for Secure Shell
(SSH)", RFC 8268, DOI 10.17487/RFC8268, December 2017,
<https://www.rfc-editor.org/info/rfc8268>.
[RFC8270] Velvindron, L. and M. Baushke, "Increase the Secure Shell
Minimum Recommended Diffie-Hellman Modulus Size to 2048
Bits", RFC 8270, DOI 10.17487/RFC8270, December 2017,
<https://www.rfc-editor.org/info/rfc8270>.
9.2. Informative References
[CNSA-SUITE]
"Information Assurance by the National Security Agency",
"Commercial National Security Algorithm Suite", September
2016, <https://www.iad.gov/iad/programs/iad-initiatives/
cnsa-suite.cfm>.
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[ECDSA-Nonce-Leak]
De Mulder, Hutter, Marson, and Pearson, "Using
Bleichenbacher's Solution to the Hidden Number Problem to
Attack Nonce Leaks in 384-Bit ECDSA", IACR Cryptology
ePrint Archive 2013, August 2013,
<https://eprint.iacr.org/2013/346.pdf>.
[I-D.ietf-curdle-gss-keyex-sha2]
Sorce, S. and H. Kario, "GSS-API Key Exchange with SHA2",
draft-ietf-curdle-gss-keyex-sha2-03 (work in progress),
December 2017.
[I-D.ietf-curdle-ssh-curves]
Adamantiadis, A., Josefsson, S., and M. Baushke, "Secure
Shell (SSH) Key Exchange Method using Curve25519 and
Curve448", draft-ietf-curdle-ssh-curves-06 (work in
progress), November 2017.
[IANA-KEX]
Internet Assigned Numbers Authority (IANA), "Secure Shell
(SSH) Protocol Parameters: Key Exchange Method Names",
January 2018, <http://www.iana.org/assignments/ssh-
parameters/ssh-parameters.xhtml#ssh-parameters-16>.
[LOGJAM] Adrian, D., Bhargavan, K., Durumeric, Z., Gaudry, P.,
Green, M., Halderman, J., Heninger, N., Springall, D.,
Thome, E., Valenta, L., VanderSloot, B., Wustrow, E.,
Zanella-Beguelin, S., and P. Zimmermann, "Imperfect
Forward Secrecy: How Diffie-Hellman Fails in Practice",
ACM Conference on Computer and Communications Security
(CCS) 2015, 2015,
<https://weakdh.org/imperfect-forward-secrecy-ccs15.pdf>.
[MFQ-U-OO-815099-15]
"National Security Agency/Central Security Service", "CNSA
Suite and Quantum Computing FAQ", January 2016,
<https://www.iad.gov/iad/library/ia-guidance/
ia-solutions-for-classified/algorithm-guidance/
cnsa-suite-and-quantum-computing-faq.cfm>.
[NIST-SP-800-131Ar1]
Barker and Roginsky, "Transitions: Recommendation for the
Transitioning of the Use of Cryptographic Algorithms and
Key Lengths", NIST Special Publication 800-131A Revision
1, November 2015,
<http://nvlpubs.nist.gov/nistpubs/SpecialPublications/
NIST.SP.800-131Ar1.pdf>.
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[RFC3174] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1
(SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001,
<https://www.rfc-editor.org/info/rfc3174>.
[RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251,
January 2006, <https://www.rfc-editor.org/info/rfc4251>.
[RFC4419] Friedl, M., Provos, N., and W. Simpson, "Diffie-Hellman
Group Exchange for the Secure Shell (SSH) Transport Layer
Protocol", RFC 4419, DOI 10.17487/RFC4419, March 2006,
<https://www.rfc-editor.org/info/rfc4419>.
[RFC4432] Harris, B., "RSA Key Exchange for the Secure Shell (SSH)
Transport Layer Protocol", RFC 4432, DOI 10.17487/RFC4432,
March 2006, <https://www.rfc-editor.org/info/rfc4432>.
[RFC4462] Hutzelman, J., Salowey, J., Galbraith, J., and V. Welch,
"Generic Security Service Application Program Interface
(GSS-API) Authentication and Key Exchange for the Secure
Shell (SSH) Protocol", RFC 4462, DOI 10.17487/RFC4462, May
2006, <https://www.rfc-editor.org/info/rfc4462>.
[RFC5656] Stebila, D. and J. Green, "Elliptic Curve Algorithm
Integration in the Secure Shell Transport Layer",
RFC 5656, DOI 10.17487/RFC5656, December 2009,
<https://www.rfc-editor.org/info/rfc5656>.
[RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security
Considerations for the SHA-0 and SHA-1 Message-Digest
Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011,
<https://www.rfc-editor.org/info/rfc6194>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/info/rfc6234>.
[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>.
[safe-curves]
Bernstein and Lange, "SafeCurves: choosing safe curves for
elliptic-curve cryptography.", February 2016,
<https://safecurves.cr.yp.to/>.
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Author's Address
Mark D. Baushke
Juniper Networks, Inc.
1133 Innovation Way
Sunnyvale, CA 94089-1228
US
Email: mdb@juniper.net
URI: http://www.juniper.net/
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