< draft-ietf-curdle-ssh-modp-dh-sha2-07.txt   draft-ietf-curdle-ssh-modp-dh-sha2-09.txt >
Internet Engineering Task Force M. Baushke Internet Engineering Task Force M. Baushke
Internet-Draft Juniper Networks, Inc. Internet-Draft Juniper Networks, Inc.
Updates: 4250, 4253 (if approved) June 22, 2017 Updates: 4250, 4253 (if approved) September 15, 2017
Intended status: Standards Track Intended status: Standards Track
Expires: December 24, 2017 Expires: March 19, 2018
More Modular Exponential (MODP) Diffie-Hellman (DH) Key Exchange (KEX) More Modular Exponential (MODP) Diffie-Hellman (DH) Key Exchange (KEX)
Groups for Secure Shell (SSH) Groups for Secure Shell (SSH)
draft-ietf-curdle-ssh-modp-dh-sha2-07 draft-ietf-curdle-ssh-modp-dh-sha2-09
Abstract Abstract
This document defines added Modular Exponential (MODP) Groups for the This document defines added Modular Exponential (MODP) Groups for the
Secure Shell (SSH) protocol using SHA-2 hashes. This document Secure Shell (SSH) protocol using SHA-2 hashes. This document
updates RFC 4250. This document updates RFC 4253. updates RFC 4250. This document updates RFC 4253 including an errata
fix for checking the Peer's DH Public Key.
Status of This Memo Status of This Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on December 24, 2017. This Internet-Draft will expire on March 19, 2018.
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1. Overview and Rationale 1. Overview and Rationale
Secure Shell (SSH) is a common protocol for secure communication on Secure Shell (SSH) is a common protocol for secure communication on
the Internet. Due to recent security concerns with SHA-1 [RFC6194] the Internet. Security protocols and primitives are an active area
and with MODP groups with less than 2048 bits [NIST-SP-800-131Ar1] for research and help to suggest updates to SSH.
implementer and users request support for larger Diffie Hellman (DH)
MODP group sizes with data integrity verification using the SHA-2 Section 3 of the [RFC4253] contains a small errata for checking the
family of secure hash algorithms as well as MODP groups providing Peer's DH Public key. Section 4 of this document provides the
more security. correction.
Due to 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 Diffie Hellman (DH) 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 use
of larger MODP groups and the move to the SHA-2 family of hashes are
important features to strengthen the key exchange algorithms
available to the SSH client and server.
DH primes being adopted by this document are all "safe primes" such DH primes being adopted by this document are all "safe primes" such
that p = 2q + 1 where q is also a prime. New MODP groups are being that p = 2q + 1 where q is also a prime. New MODP groups are being
introduced starting with the MODP 3072-bit group 15 all use SHA512 as introduced starting with the MODP 3072-bit group 15. All use SHA512
the hash algorithm. as the hash algorithm.
The DH 2048-bit MODP group 14 is already present in most SSH The DH 2048-bit MODP group 14 is already present in most SSH
implementations and most implementations already have a SHA256 implementations and most implementations already have a SHA256
implementation, so diffie-hellman-group14-sha256 is provided as easy implementation, so diffie-hellman-group14-sha256 is provided as easy
to implement. to implement.
It is intended that these new MODP groups with SHA-2 based hashes It is intended that these new MODP groups with SHA-2 based hashes
update the [RFC4253] section 6.4 and [RFC4250] section 4.10 update the [RFC4253] section 6.4 and [RFC4250] section 4.10
standards. standards.
skipping to change at page 3, line 41 skipping to change at page 3, line 41
curdle@ietf.org.] 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 RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
3. Key Exchange Algorithms 3. Key Exchange Algorithms
This memo adopts the style and conventions of [RFC4253] in specifying This document adds some new Key Exchange Algorithm Method Names in
how the use of new data key exchange is indicated in SSH. [RFC4253] and [RFC4250].
The following new key exchange algorithms are defined: This document adopts the style and conventions of [RFC4253] in
specifying how the use of new data key exchange is indicated in SSH.
Key Exchange Method Name The following new key exchange method algorithms are defined:
diffie-hellman-group14-sha256
diffie-hellman-group15-sha512
diffie-hellman-group16-sha512
diffie-hellman-group17-sha512
diffie-hellman-group18-sha512
Figure 1 o diffie-hellman-group14-sha256
o diffie-hellman-group15-sha512
o diffie-hellman-group16-sha512
o diffie-hellman-group17-sha512
o diffie-hellman-group18-sha512
The SHA-2 family of secure hash algorithms are defined in [RFC6234]. The SHA-2 family of secure hash algorithms are defined in [RFC6234].
The method of key exchange used for the name "diffie-hellman- The method of key exchange used for the name "diffie-hellman-
group14-sha256" is the same as that for "diffie-hellman-group14-sha1" group14-sha256" is the same as that for "diffie-hellman-group14-sha1"
except that the SHA256 hash algorithm is used. It is recommended except that the SHA256 hash algorithm is used. It is recommended
that diffie-hellman-group14-sha256 SHOULD be supported to smooth the that diffie-hellman-group14-sha256 SHOULD be supported to smooth the
transition to newer group sizes. transition to newer group sizes.
The group15 through group18 names are the same as those specified in The group15 through group18 names are the same as those specified in
skipping to change at page 5, line 17 skipping to change at page 5, line 9
violated, then the key exchange fails. violated, then the key exchange fails.
This simple check ensures: This simple check ensures:
o The remote peer behaves properly. o The remote peer behaves properly.
o The local system is not forced into the two-element subgroup. o The local system is not forced into the two-element subgroup.
5. IANA Considerations 5. IANA Considerations
This document augments the Key Exchange Method Names in [RFC4253] and
[RFC4250].
IANA is requested to add to the Key Exchange Method Names algorithm IANA is requested to add to the Key Exchange Method Names algorithm
registry [IANA-KEX] with the following entries: registry [IANA-KEX] with the following entries:
Key Exchange Method Name Reference Key Exchange Method Name Reference
----------------------------- ---------- ----------------------------- ----------
diffie-hellman-group14-sha256 This Draft diffie-hellman-group14-sha256 This Draft
diffie-hellman-group15-sha512 This Draft diffie-hellman-group15-sha512 This Draft
diffie-hellman-group16-sha512 This Draft diffie-hellman-group16-sha512 This Draft
diffie-hellman-group17-sha512 This Draft diffie-hellman-group17-sha512 This Draft
diffie-hellman-group18-sha512 This Draft diffie-hellman-group18-sha512 This Draft
skipping to change at page 6, line 11 skipping to change at page 6, line 4
Symmetric Keys. Care should be taken to use sufficient entropy and/ Symmetric Keys. Care should be taken to use sufficient entropy and/
or DRBG algorithms to maximize the true security strength of the key or DRBG algorithms to maximize the true security strength of the key
exchange and ciphers selected. exchange and ciphers selected.
Using a fixed set of Diffie-Hellman parameters makes them a high Using a fixed set of Diffie-Hellman parameters makes them a high
value target for pre-computation. Generating additional sets of value target for pre-computation. Generating additional sets of
primes to be used, or moving to larger values is a mitigation against primes to be used, or moving to larger values is a mitigation against
this issue. this issue.
8. References 8. References
8.1. Normative References 8.1. Normative References
[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>. <https://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>. <https://www.rfc-editor.org/info/rfc3526>.
[RFC4250] Lehtinen, S. and C. Lonvick, Ed., "The Secure Shell (SSH) [RFC4250] Lehtinen, S. and C. Lonvick, Ed., "The Secure Shell (SSH)
Protocol Assigned Numbers", RFC 4250, Protocol Assigned Numbers", RFC 4250,
DOI 10.17487/RFC4250, January 2006, DOI 10.17487/RFC4250, January 2006,
<http://www.rfc-editor.org/info/rfc4250>. <https://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, <https://www.rfc-editor.org/info/rfc4253>.
[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>.
8.2. Informative References 8.2. Informative References
[IANA-KEX] [IANA-KEX]
Internet Assigned Numbers Authority (IANA), "Secure Shell Internet Assigned Numbers Authority (IANA), "Secure Shell
(SSH) Protocol Parameters: Key Exchange Method Names", (SSH) Protocol Parameters: Key Exchange Method Names",
March 2017, <http://www.iana.org/assignments/ssh- March 2017, <http://www.iana.org/assignments/ssh-
parameters/ssh-parameters.xhtml#ssh-parameters-16>. parameters/ssh-parameters.xhtml#ssh-parameters-16>.
[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/
for-classified/algorithm-guidance/cnsa-suite-and-quantum- ia-solutions-for-classified/algorithm-guidance/
computing-faq.cfm>. cnsa-suite-and-quantum-computing-faq.cfm>.
[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>.
[RFC3766] Orman, H. and P. Hoffman, "Determining Strengths For [RFC3766] Orman, H. and P. Hoffman, "Determining Strengths For
Public Keys Used For Exchanging Symmetric Keys", BCP 86, Public Keys Used For Exchanging Symmetric Keys", BCP 86,
RFC 3766, DOI 10.17487/RFC3766, April 2004, RFC 3766, DOI 10.17487/RFC3766, April 2004,
<http://www.rfc-editor.org/info/rfc3766>. <https://www.rfc-editor.org/info/rfc3766>.
[RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security [RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security
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>. <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,
<http://www.rfc-editor.org/info/rfc6234>.
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 Phone: +1 408 745 2952
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