< draft-ietf-curdle-ssh-kex-sha2-06.txt   draft-ietf-curdle-ssh-kex-sha2-07.txt >
Internet Engineering Task Force M. Baushke Internet Engineering Task Force M. Baushke
Internet-Draft Juniper Networks, Inc. Internet-Draft Juniper Networks, Inc.
Updates: 4253, 4419, 4432, 4462, 5656 September 20, 2016 Updates: 4250, 4253 (if approved) March 27, 2017
(if approved)
Intended status: Standards Track Intended status: Standards Track
Expires: March 24, 2017 Expires: September 28, 2017
Key Exchange (KEX) Method Updates and Recommendations for Secure Shell Key Exchange (KEX) Method Updates and Recommendations for Secure Shell
(SSH) (SSH)
draft-ietf-curdle-ssh-kex-sha2-06 draft-ietf-curdle-ssh-kex-sha2-07
Abstract Abstract
This document adds recommendations for adoption of ssh-curves from This document is intended to update the recommended set of key
the [I-D.ietf-curdle-ssh-curves] and new-modp from the exchange methods for use in the Secure Shell (SSH) protocol to meet
[I-D.ietf-curdle-ssh-modp-dh-sha2], and deprecates some previously evolving needs for stronger security. This RFC updates [RFC4253]
specified Key Exchange Method algorithm names for the Secure Shell MUST algorithms. This RFC also notes that the [IANASSH] has replaced
(SSH) protocol. It also updates [RFC4253], [RFC4419], [RFC4462], and [RFC4250] as the primary reference document for SSH Protocol Assigned
[RFC5656] by specifying the set key exchange algorithms that Numbers.
currently exist and which ones MUST, SHOULD, MAY, and SHOULD NOT be
implemented. New key exchange methods use the SHA-2 family of This document adds recommendations for adoption of Key Exchange
hashes. Methods which MUST, SHOULD+, SHOULD, SHOULD-, MAY, SHOULD NOT, and
MUST NOT be implemented. New key exchange methods will use the SHA-2
family of hashes and are drawn from these from
[I-D.ietf-curdle-ssh-curves] and new-modp from the
[I-D.ietf-curdle-ssh-modp-dh-sha2] and gss-keyex [NEWGSSAPI].
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on March 24, 2017. This Internet-Draft will expire on September 28, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
1. Overview and Rationale Table of Contents
Secure Shell (SSH) is a common protocol for secure communication on
the Internet. In [RFC4253], SSH originally defined the Key Exchange
Method Name diffie-hellman-group1-sha1 which used [RFC2409] 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 [NIST-SP-800-131Ar1] implementer and users request
support for larger MODP group sizes with data integrity verification
using the SHA-2 family of secure hash algorithms as well as MODP
groups providing more security.
The United States Information Assurance Directorate (IAD) at the 1. Overview and Rationale . . . . . . . . . . . . . . . . . . . 2
National Security Agency (NSA) has published a FAQ 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
[MFQ-U-OO-815099-15] suggesting that the use of Elliptic Curve 3. Key Exchange Methods . . . . . . . . . . . . . . . . . . . . 3
Diffie-Hellman (ECDH) using the nistp256 curve and SHA-2 based hashes 3.1. curve25519-sha256 . . . . . . . . . . . . . . . . . . . . 4
less than SHA2-384 are no longer sufficient for transport of Top 3.2. diffie-hellman-group-exchange-sha1 . . . . . . . . . . . 4
Secret information. It is for this reason that this draft moves 3.3. diffie-hellman-group1-sha1 . . . . . . . . . . . . . . . 4
ecdh-sha2-nistp256 from a REQUIRED to OPTIONAL as a key exchange 3.4. diffie-hellman-group14-sha1 . . . . . . . . . . . . . . . 4
method. This is the same reason that the stronger MODP groups being 3.5. diffie-hellman-group14-sha256 . . . . . . . . . . . . . . 4
adopted. As the MODP group14 is already present in most SSH 3.6. diffie-hellman-group16-sha512 . . . . . . . . . . . . . . 4
implementations and most implementations already have a SHA2-256 3.7. ecdh-sha2-nistp256 . . . . . . . . . . . . . . . . . . . 5
implementation, so diffie-hellman-group14-sha256 is provided as an 3.8. ecdh-sha2-nistp384 . . . . . . . . . . . . . . . . . . . 5
easy to implement and faster to use key exchange. Small embedded 3.9. gss-gex-sha1-* . . . . . . . . . . . . . . . . . . . . . 5
applications may find this KEX desirable to use. 3.10. gss-group1-sha1-* . . . . . . . . . . . . . . . . . . . . 5
3.11. gss-group14-sha1-* . . . . . . . . . . . . . . . . . . . 5
3.12. gss-group14-sha256-* . . . . . . . . . . . . . . . . . . 6
3.13. gss-group16-sha512-* . . . . . . . . . . . . . . . . . . 6
3.14. rsa1024-sha1 . . . . . . . . . . . . . . . . . . . . . . 6
4. Summary Guidance for Key Exchange Method Names . . . . . . . 6
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
The NSA Information Assurance Directorate (IAD) has also published 1. Overview and Rationale
the Commercial National Security Algorithm Suite (CNSA Suite)
[CNSA-SUITE] in which the 3072-bit MODP Group 15 in RFC 3526 is
explicitly mentioned as the minimum modulus to protect Top Secret
communications.
It has been observed in [safe-curves] that the NIST recommended Secure Shell (SSH) is a common protocol for secure communication on
Elliptic Curve Prime Curves (P-256, P-384, and P-521) are perhaps not the Internet. In [RFC4253], SSH originally defined two Key Exchange
the best available for Elliptic Curve Cryptography (ECC) Security. Method Names that MUST be implemented. Over time, what was once
For this reason, none of the [RFC5656] curves are marked as a MUST considered secure, is no longer considered secure. The purpose of
implement. However, the requirement that "every compliant SSH ECC this RFC is to recommend that some published key exchanges be adopted
implementation MUST implement ECDH key exchange" is now taken to mean or reclassified and others retired.
that if ecdsa-sha2-[identifier] is implemented, then ecdh-
sha2-[identifier] MUST be implemented.
Please send comments on this draft to curdle@ietf.org. [TO BE REMOVED: Please send comments on this draft to
curdle@ietf.org.]
2. Requirements Language 2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Key Exchange Algorithms When used in the tables in this document, these terms indicate that
the listed algorithm MUST, MUST NOT, SHOULD, SHOULD NOT or MAY be
implemented as part of a Secure Shell implementation. Additional
terms used in this document are:
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.
3. Key Exchange Methods
This memo adopts the style and conventions of [RFC4253] in specifying This memo adopts the style and conventions of [RFC4253] in specifying
how the use of new data key exchange is indicated in SSH. how the use of data key exchange is indicated in SSH.
A new set of Elliptic Curve Diffie-Hellman ssh-curves exist. The This RFC also collects Key Exchange Method Names in various existing
curve25519-sha256 MUST be adopted where possible. RFCs [RFC4253], [RFC4419], [RFC4432], [RFC4462], [RFC5656],
[I-D.ietf-curdle-ssh-modp-dh-sha2], [NEWGSSAPI], and
[I-D.ietf-curdle-ssh-curves] and provides a suggested suitability for
implementation of MUST, SHOULD+, SHOULD, SHOULD-, SHOULD NOT, and
MUST NOT.
As a hedge against uncertainty raised by the NSA IAD FAQ publication, This document is intended to provide guidance as to what Key Exchange
new MODP Diffie-Hellman based key exchanges are proposed for Algorithms are to be considered for new or updated SSH
inclusion in the set of key exchange method names as well as the implementations. This document will be superseded when one or more
curve448-sha512 curve. of the listed algorithms are considered too weak to continue to use
securely, 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.
The following new key exchange algorithms are defined: 3.1. curve25519-sha256
Key Exchange Method Name Note The Curve25519 provides strong security and is efficient on a wide
----------------------------- ------------------ range of architectures with properties that allow better
curve25519-sha256 MUST/REQUIRED implementation properties compared to traditional elliptic curves.
curve448-sha512 MAY/OPTIONAL The use of SHA2-256 for integrity is a reasonable one for this
diffie-hellman-group14-sha256 MUST/REQUIRED method. This Key Exchange Method has a few implementations and
diffie-hellman-group15-sha512 MAY/OPTIONAL SHOULD+ be implemented in any SSH interested in using elliptic curve
diffie-hellman-group16-sha512 SHOULD/RECOMMENDED based key exchanges.
diffie-hellman-group17-sha512 MAY/OPTIONAL
diffie-hellman-group18-sha512 MAY/OPTIONAL
gss-group14-sha256-* SHOULD/RECOMMENDED
gss-group15-sha512-* MAY/OPTIONAL
gss-group16-sha512-* SHOULD/RECOMMENDED
gss-group17-sha512-* MAY/OPTIONAL
gss-group18-sha512-* MAY/OPTIONAL
The SHA-2 family of secure hash algorithms are defined in 3.2. diffie-hellman-group-exchange-sha1
[FIPS-180-4].
4. IANA Considerations 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 MUST NOT be
implemented.
This RFC augments the Key Exchange Method Names in [RFC4253]. It 3.3. diffie-hellman-group1-sha1
downgrades the use of SHA-1 hashing for key exchange methods in
[RFC4419], [RFC4432], and [RFC4462]. It also moves from MUST to
SHOULD the ecdh-sha2-nistp256 given in [RFC5656].
It adds a new set of named "gss-*" methods to [RFC4462] with a MAY This method uses [RFC2409] Oakley Group 2 (a 1024-bit MODP group) and
recommendation. SHA-1 [RFC3174]. Due to recent security concerns with SHA-1
[RFC6194] and with MODP groups with less than 2048 bits
[NIST-SP-800-131Ar1], this method is considered insecure. This
method is being moved from MUST to MUST NOT.
It is desirable to also include the new-modp from the 3.4. diffie-hellman-group14-sha1
[I-D.ietf-curdle-ssh-modp-dh-sha2] in this list.
It is desirable to also include the ssh-curves from the This generated key exchange groups uses SHA-1 which has security
[I-D.ietf-curdle-ssh-curves] in this list. The "curve25519-sha256" concerns [RFC6194]. However, this group is still strong enough and
is currently available in some Secure Shell implementations under the is widely deployed. This method is being moved from MUST to SHOULD-
name "curve25519-sha256@libssh.org" and is the best candidate for a to aid in transition to stronger SHA-2 based hashes. This method
fast, safe, and secure key exchange method. will transition to MUST NOT when SHA-2 alternatives are more
generally available.
IANA is requested to update the SSH algorithm registry to ensure that 3.5. diffie-hellman-group14-sha256
all of the listed Key Exchange Method Name and References exist in
the following table. However, the Implement column is just the
current recommendations of this RFC.
Key Exchange Method Name Reference Implement This generated key exchange uses a 2048-bit sized MODP group along
------------------------------------ ---------- ---------- with a SHA-2 (SHA2-256) hash. This represents the smallest Finite
curve25519-sha256 ssh-curves MUST Field cryptography Diffie-Hellman key exchange method. It is a
curve448-sha512 ssh-curves MAY reasonably simple transition to move from SHA-1 to SHA-2. This
diffie-hellman-group-exchange-sha1 RFC4419 SHOULD NOT method MUST be implemented.
diffie-hellman-group-exchange-sha256 RFC4419 MAY
diffie-hellman-group1-sha1 RFC4253 SHOULD NOT
diffie-hellman-group14-sha1 RFC4253 SHOULD
diffie-hellman-group14-sha256 new-modp MUST
diffie-hellman-group15-sha512 new-modp MAY
diffie-hellman-group16-sha512 new-modp SHOULD
diffie-hellman-group17-sha512 new-modp MAY
diffie-hellman-group18-sha512 new-modp MAY
ecdh-sha2-nistp256 RFC5656 SHOULD
ecdh-sha2-nistp384 RFC5656 SHOULD
ecdh-sha2-nistp521 RFC5656 SHOULD
ecdh-sha2-* RFC5656 MAY
ecmqv-sha2 RFC5656 SHOULD NOT
gss-gex-sha1-* RFC4462 SHOULD NOT
gss-group1-sha1-* RFC4462 SHOULD NOT
gss-group14-sha1-* RFC4462 SHOULD
gss-group14-sha256-* new-modp SHOULD
gss-group15-sha512-* new-modp MAY
gss-group16-sha512-* new-modp SHOULD
gss-group17-sha512-* new-modp MAY
gss-group18-sha512-* new-modp MAY
gss-* RFC4462 MAY
rsa1024-sha1 RFC4432 SHOULD NOT
rsa2048-sha256 RFC4432 MAY
The Implement column in the above table is a suggestion/ 3.6. diffie-hellman-group16-sha512
recommendation for the listed key exchange method to be implemented
in the default list of key exchange methods. It is up to the end-
user as to what algorithms they choose to be able to negotiate, so
the KEX algorithms should be configurable by the administrator of the
server as well as the user of the client. This RFC is intended to
provide IANA defined names for these groups for interoperability.
The Note column of the IANA table should probably continue to point
to the implementation detail sections of the Reference RFCs where
appropriate.
The guidance of his RFC is that the SHA-1 algorithm hashing SHOULD The use of FFC DH is well understood and trusted. Adding larger
NOT be used. If it is used, it should only be provided for backwards modulus sizes and protecting with SHA2-512 should give enough head
compatibility, should not be used in new designs, and should be room to be ready for the next scare that someone has pre-computed.
phased out of existing key exchanges as quickly as possible because This modulus is larger than that required by [CNSA-SUITE] and should
of its known weaknesses. Any key exchange using SHA-1 SHOULD NOT be be sufficient to inter-operate with more paranoid nation-states.
in a default key exchange list if at all possible. If they are This method SHOULD+ be implemented.
needed for backward compatibility, they SHOULD be listed after all of
the SHA-2 based key exchanges.
The RFC4253 REQUIRED diffie-hellman-group14-sha1 method SHOULD be 3.7. ecdh-sha2-nistp256
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.
The SSH development community is divided on this and many
implementations do exist. However, there are good implementations of
this along with a constant-time SHA2-256 implementation. If an
implementer does not have a constant-time SHA2-384 implementation
(which helps avoid side-channel attacks), then this is the correct
ECDH to implement. This method SHOULD- be implemented.
3.8. ecdh-sha2-nistp384
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 for now. This really needs a constant-time implementation of
SHA2-384 to be useful. This method SHOULD+ be implemented.
3.9. gss-gex-sha1-*
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 MUST NOT be
implemented.
3.10. gss-group1-sha1-*
This method suffers from the same problems of diffie-hellman-
group1-sha1. It uses [RFC2409] 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
[NIST-SP-800-131Ar1], this method is considered insecure. This
method MUST NOT be implemented.
3.11. gss-group14-sha1-*
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.
3.12. gss-group14-sha256-*
If the GSS-API is to be used, then this method SHOULD be implemented.
3.13. gss-group16-sha512-*
If the GSS-API is to be used, then this method SHOULD+ be
implemented.
3.14. rsa1024-sha1
The security of RSA 1024-bit modulus keys is not good enough any
longer. A minimum bit size should be 2048-bit groups. This
generated key exchange groups uses SHA-1 which has security concerns
[RFC6194]. This method MUST NOT be implemented.
4. Summary Guidance for Key Exchange Method Names
The full set of official [IANASSH] key algorithm method names not
otherwise mentioned in this RFC MAY be implemented.
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 MUST NOT
diffie-hellman-group1-sha1 RFC4253 MUST NOT
diffie-hellman-group14-sha1 RFC4253 SHOULD-
diffie-hellman-group14-sha256 new-modp MUST
diffie-hellman-group16-sha512 new-modp SHOULD+
ecdh-sha2-nistp256 RFC5656 SHOULD-
ecdh-sha2-nistp384 RFC5656 SHOULD+
gss-gex-sha1-* RFC4462 MUST NOT
gss-group1-sha1-* RFC4462 MUST NOT
gss-group14-sha1-* RFC4462 SHOULD-
gss-group14-sha256-* gss-keyex SHOULD
gss-group16-sha512-* gss-keyex SHOULD+
rsa1024-sha1 RFC4432 MUST NOT
The guidance of this RFC is that the SHA-1 algorithm hashing MUST 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 MUST NOT be in a default key exchange list if 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. retained for compatibility with older Secure Shell implementations.
It is intended that this key exchange method be phased out as soon as It is intended that this key exchange method be phased out as soon as
possible. possible.
It is believed that all current SSH implementations should be able to It is believed that all current SSH implementations should be able to
achieve an implementation of the "diffie-hellman-group14-sha256" achieve an implementation of the "diffie-hellman-group14-sha256"
method. To that end, this is one method that MUST be implemented. method. To that end, this is one method that MUST be implemented.
If GSS-API methods are available, then the RFC4462 REQUIRED gss-
group14-sha1-* method SHOULD be retained for compatibility with older
Secure Shell implementations and the gss-groups14-sha256-* method
SHOULD be added as for "sha1".
[TO BE REMOVED: This registration should take place at the following [TO BE REMOVED: This registration should take place at the following
location: <http://www.iana.org/assignments/ssh-parameters/ssh- location: <http://www.iana.org/assignments/ssh-parameters/ssh-
parameters.xhtml#ssh-parameters-16>] parameters.xhtml#ssh-parameters-16>]
5. Acknowledgements 5. Acknowledgements
Thanks to the following people for review and comments: Denis Bider, Thanks to the following people for review and comments: Denis Bider,
Peter Gutmann, Damien Miller, Niels Moeller, Matt Johnston, Iwamoto Peter Gutmann, Damien Miller, Niels Moeller, Matt Johnston, Iwamoto
Kouichi, Simon Josefsson, Dave Dugal, Daniel Migault. Kouichi, Simon Josefsson, Dave Dugal, Daniel Migault, Anna Johnston.
Thanks to the following people for code to implement interoperable Thanks to the following people for code to implement inter-operable
exchanges using some of these groups as found in an this draft: exchanges using some of these groups as found in an this draft:
Darren Tucker for OpenSSH and Matt Johnston for Dropbear. And thanks Darren Tucker for OpenSSH and Matt Johnston for Dropbear. And thanks
to Iwamoto Kouichi for information about RLogin, Tera Term (ttssh) to Iwamoto Kouichi for information about RLogin, Tera Term (ttssh)
and Poderosa implementations also adopting new Diffie-Hellman groups and Poderosa implementations also adopting new Diffie-Hellman groups
based on this draft. based on this draft.
6. Security Considerations 6. Security Considerations
The security considerations of [RFC4253] apply to this RFC. The security considerations of [RFC4253] apply to this RFC.
The security considerations of [RFC3526] suggest that these MODP It is desirable to deprecate or remove key exchange method name that
groups have security strengths given in this table. They are based are considered weak. A key exchange method may be weak because too
on [RFC3766] Determining Strengths For Public Keys Used For few bits are used, or the hashing algorithm is considered too weak.
Exchanging Symmetric Keys.
Group modulus security strength estimates (RFC3526) The diffie-hellman-group1-sha1 is being moved from MUST to MUST NOT.
This method used [RFC2409] 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
[NIST-SP-800-131Ar1], this method is no longer considered secure.
+--------+----------+---------------------+---------------------+ The United States Information Assurance Directorate (IAD) at the
| Group | Modulus | Strength Estimate 1 | Strength Estimate 2 | National Security Agency (NSA) has published a FAQ
| | +----------+----------+----------+----------+ [MFQ-U-OO-815099-15] suggesting that the use of Elliptic Curve
| | | | exponent | | exponent | Diffie-Hellman (ECDH) using the nistp256 curve and SHA-2 based hashes
| | | in bits | size | in bits | size | less than SHA2-384 are no longer sufficient for transport of Top
+--------+----------+----------+----------+----------+----------+ Secret information. It is for this reason that this draft moves
| 14 | 2048-bit | 110 | 220- | 160 | 320- | ecdh-sha2-nistp256 from a MUST to MAY as a key exchange method. This
| 15 | 3072-bit | 130 | 260- | 210 | 420- | is the same reason that the stronger MODP groups being adopted. As
| 16 | 4096-bit | 150 | 300- | 240 | 480- | the MODP group14 is already present in most SSH implementations and
| 17 | 6144-bit | 170 | 340- | 270 | 540- | most implementations already have a SHA2-256 implementation, so
| 18 | 8192-bit | 190 | 380- | 310 | 620- | 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.
Figure 1 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.
Many users seem to be interested in the perceived safety of using It has been observed in [safe-curves] that the NIST Elliptic Curve
larger MODP groups and hashing with SHA2-based algorithms. 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.
7. References 7. References
7.1. Normative References 7.1. Normative References
[FIPS-180-4]
National Institute of Standards and Technology, "Secure
Hash Standard (SHS)", FIPS PUB 180-4, August 2015,
<http://nvlpubs.nist.gov/nistpubs/FIPS/
NIST.FIPS.180-4.pdf>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC3526] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP) [RFC3526] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP)
Diffie-Hellman groups for Internet Key Exchange (IKE)", Diffie-Hellman groups for Internet Key Exchange (IKE)",
RFC 3526, DOI 10.17487/RFC3526, May 2003, RFC 3526, DOI 10.17487/RFC3526, May 2003,
<http://www.rfc-editor.org/info/rfc3526>. <http://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,
<http://www.rfc-editor.org/info/rfc4250>.
[RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) [RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253, Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
January 2006, <http://www.rfc-editor.org/info/rfc4253>. January 2006, <http://www.rfc-editor.org/info/rfc4253>.
7.2. Informative References 7.2. Informative References
[CNSA-SUITE] [CNSA-SUITE]
"Information Assurance by the National Security Agency", "Information Assurance by the National Security Agency",
"Commercial National Security Algorithm Suite", September "Commercial National Security Algorithm Suite", September
2016, <https://www.iad.gov/iad/programs/iad-initiatives/ 2016, <https://www.iad.gov/iad/programs/iad-initiatives/
cnsa-suite.cfm>. cnsa-suite.cfm>.
[I-D.ietf-curdle-ssh-curves] [I-D.ietf-curdle-ssh-curves]
Adamantiadis, A. and S. Josefsson, "Secure Shell (SSH) Key Adamantiadis, A. and S. Josefsson, "Secure Shell (SSH) Key
Exchange Method using Curve25519 and Curve448", draft- Exchange Method using Curve25519 and Curve448", draft-
ietf-curdle-ssh-curves-00 (work in progress), March 2016. ietf-curdle-ssh-curves-00 (work in progress), March 2016.
[I-D.ietf-curdle-ssh-modp-dh-sha2] [I-D.ietf-curdle-ssh-modp-dh-sha2]
Baushke, M., "More Modular Exponential (MODP) Diffie- Baushke, M., "More Modular Exponential (MODP) Diffie-
Hellman (DH) Key Exchange (KEX) Groups for Secure Shell Hellman (DH) Key Exchange (KEX) Groups for Secure Shell
(SSH)", draft-ietf-curdle-ssh-modp-dh-sha2-00 (work in (SSH)", draft-ietf-curdle-ssh-modp-dh-sha2-03 (work in
progress), September 2016. progress), March 2017.
[IANASSH] "Internet Assigned Numbers Authority", "IANA, Secure Shell
(SSH) Protocol Parameters", March 2017,
<http://www.iana.org/assignments/ssh-parameters/
ssh-parameters.xhtml>.
[MFQ-U-OO-815099-15] [MFQ-U-OO-815099-15]
"National Security Agency/Central Security Service", "CNSA "National Security Agency/Central Security Service", "CNSA
Suite and Quantum Computing FAQ", January 2016, Suite and Quantum Computing FAQ", January 2016,
<https://www.iad.gov/iad/library/ia-guidance/ia-solutions- <https://www.iad.gov/iad/library/ia-guidance/ia-solutions-
for-classified/algorithm-guidance/cnsa-suite-and-quantum- for-classified/algorithm-guidance/cnsa-suite-and-quantum-
computing-faq.cfm>. computing-faq.cfm>.
[NEWGSSAPI]
Sorce, S. and H. Kario, "GSS-API Key Exchange with SHA2",
December 2016, <https://tools.ietf.org/html/draft-ssorce-
gss-keyex-sha2-00>.
[NIST-SP-800-131Ar1] [NIST-SP-800-131Ar1]
Barker, and Roginsky, "Transitions: Recommendation for the Barker, and Roginsky, "Transitions: Recommendation for the
Transitioning of the Use of Cryptographic Algorithms and Transitioning of the Use of Cryptographic Algorithms and
Key Lengths", NIST Special Publication 800-131A Revision Key Lengths", NIST Special Publication 800-131A Revision
1, November 2015, 1, November 2015,
<http://nvlpubs.nist.gov/nistpubs/SpecialPublications/ <http://nvlpubs.nist.gov/nistpubs/SpecialPublications/
NIST.SP.800-131Ar1.pdf>. NIST.SP.800-131Ar1.pdf>.
[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange [RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, DOI 10.17487/RFC2409, November 1998, (IKE)", RFC 2409, DOI 10.17487/RFC2409, November 1998,
<http://www.rfc-editor.org/info/rfc2409>. <http://www.rfc-editor.org/info/rfc2409>.
[RFC3174] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1 [RFC3174] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1
(SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001, (SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001,
<http://www.rfc-editor.org/info/rfc3174>. <http://www.rfc-editor.org/info/rfc3174>.
[RFC3766] Orman, H. and P. Hoffman, "Determining Strengths For
Public Keys Used For Exchanging Symmetric Keys", BCP 86,
RFC 3766, DOI 10.17487/RFC3766, April 2004,
<http://www.rfc-editor.org/info/rfc3766>.
[RFC4419] Friedl, M., Provos, N., and W. Simpson, "Diffie-Hellman [RFC4419] Friedl, M., Provos, N., and W. Simpson, "Diffie-Hellman
Group Exchange for the Secure Shell (SSH) Transport Layer Group Exchange for the Secure Shell (SSH) Transport Layer
Protocol", RFC 4419, DOI 10.17487/RFC4419, March 2006, Protocol", RFC 4419, DOI 10.17487/RFC4419, March 2006,
<http://www.rfc-editor.org/info/rfc4419>. <http://www.rfc-editor.org/info/rfc4419>.
[RFC4432] Harris, B., "RSA Key Exchange for the Secure Shell (SSH) [RFC4432] Harris, B., "RSA Key Exchange for the Secure Shell (SSH)
Transport Layer Protocol", RFC 4432, DOI 10.17487/RFC4432, Transport Layer Protocol", RFC 4432, DOI 10.17487/RFC4432,
March 2006, <http://www.rfc-editor.org/info/rfc4432>. March 2006, <http://www.rfc-editor.org/info/rfc4432>.
[RFC4462] Hutzelman, J., Salowey, J., Galbraith, J., and V. Welch, [RFC4462] Hutzelman, J., Salowey, J., Galbraith, J., and V. Welch,
skipping to change at page 9, line 4 skipping to change at page 11, line 6
Considerations for the SHA-0 and SHA-1 Message-Digest Considerations for the SHA-0 and SHA-1 Message-Digest
Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011, Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011,
<http://www.rfc-editor.org/info/rfc6194>. <http://www.rfc-editor.org/info/rfc6194>.
[safe-curves] [safe-curves]
Bernstein, and Lange, "SafeCurves: choosing safe curves Bernstein, and Lange, "SafeCurves: choosing safe curves
for elliptic-curve cryptography.", February 2016, for elliptic-curve cryptography.", February 2016,
<https://safecurves.cr.yp.to/>. <https://safecurves.cr.yp.to/>.
Author's Address Author's Address
Mark D. Baushke Mark D. Baushke
Juniper Networks, Inc. Juniper Networks, Inc.
1133 Innovation Way 1133 Innovation Way
Sunnyvale, CA 94089-1228 Sunnyvale, CA 94089-1228
US US
Phone: +1 408 745 2952
Email: mdb@juniper.net Email: mdb@juniper.net
URI: http://www.juniper.net/ URI: http://www.juniper.net/
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