Internet DRAFT - draft-moskowitz-orchid-cshake
draft-moskowitz-orchid-cshake
HIP R. Moskowitz
Internet-Draft HTT Consulting
Updates: 7343 (if approved) S. Card
Intended status: Standards Track A. Wiethuechter
Expires: 22 November 2020 AX Enterprize
21 May 2020
Using cSHAKE in ORCHIDs
draft-moskowitz-orchid-cshake-01
Abstract
This document specifies how to use the cSHAKE hash for ORCHID
generation and allows for varying sized hashes in the ORCHID along
with additional information within the ORCHID. It is an addendum to
ORCHIDv2 [RFC7343].
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terms, Notation and Definitions . . . . . . . . . . . . . . . 2
2.1. Requirements Terminology . . . . . . . . . . . . . . . . 2
2.2. Notation . . . . . . . . . . . . . . . . . . . . . . . . 3
2.3. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
3. Adding additional information to the ORCHID . . . . . . . . . 3
4. ORCHID Decoding . . . . . . . . . . . . . . . . . . . . . . . 4
5. ORCHID Encoding . . . . . . . . . . . . . . . . . . . . . . . 4
6. Initial use case for cSHAKE . . . . . . . . . . . . . . . . . 5
7. Initial use case for Additional Information . . . . . . . . . 5
8. Collision risks with Hierarchical HITs . . . . . . . . . . . 5
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
10. Security Considerations . . . . . . . . . . . . . . . . . . . 6
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
11.1. Normative References . . . . . . . . . . . . . . . . . . 6
11.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Calculating Collision Probabilities . . . . . . . . 7
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
This document adds the [Keccak] based cSHAKE XOF hash function from
NIST SP 800-185 [NIST.SP.800-185] to ORCHIDv2 [RFC7343]. cSHAKE is a
variable output length hash function. As such it does not use the
truncation operation that other hashes need. The invocation of
cSHAKE specifies the desired number of bits in the hash output.
cSHAKE is used, rather than SHAKE from NIST FIPS 202 [NIST.FIPS.202],
as cSHAKE has a parameter 'S' as a customization bit string. This
parameter will be used for including the ORCHID Context Identifier in
a standard fashion.
An additional change to ORCHID construction will allow for shorter
hash output lengths to permit inclusion of additional information
like Hierarchical HITs [hierarchical-hit] into the ORCHID.
2. Terms, Notation and Definitions
2.1. Requirements Terminology
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.
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2.2. Notation
| Signifies concatenation of information - e.g., X | Y is the
concatenation of X and Y.
2.3. Definitions
Keccak (KECCAK Message Authentication Code):
The family of all sponge functions with a KECCAK-f permutation as
the underlying function and multi-rate padding as the padding
rule.
cSHAKE (The customizable SHAKE function):
Extends the SHAKE scheme to allow users to customize their use of
the function.
SHAKE (Secure Hash Algorithm KECCAK):
A secure hash that allows for an arbitrary output length.
XOF (eXtendable-Output Function):
A function on bit strings (also called messages) in which the
output can be extended to any desired length.
3. Adding additional information to the ORCHID
ORCHIDv2 [RFC7343] is currently defined as consisting of three
components:
ORCHID := Prefix | OGA ID | Encode_96( Hash )
where:
Prefix : A constant 28-bit-long bitstring value
(IANA IPv6 assigned).
OGA ID : A 4-bit long identifier for the Hash_function
in use within the specific usage context.
Encode_96( ) : An extraction function in which output is obtained
by extracting the middle 96-bit-long bitstring
from the argument bitstring.
This addendum will be constructed as follows:
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ORCHID := Prefix | OGA ID | Info (n) | Hash (m)
where:
Prefix : A constant 28-bit-long bitstring value
(IANA IPv6 assigned).
OGA ID : A 4-bit long identifier for the Hash_function
in use within the specific usage context.
Info (n) : n bits of information that define a use of the
ORCHID. n can be zero, that is no additional
information.
Hash (m) : An extraction function in which output is m bits.
n + m = 96 bits
The 96 bits currently allocated to the Encode_96 function can be
divided in any manner between the additional information and the hash
output. Care must be taken in determining the size of the hash
portion, taking into account risks like pre-image attacks. Thus 64
bits as used in Hierarchical HITs may be as small as is acceptable.
4. ORCHID Decoding
With this addendum, the decoding of an ORCHID is determined by the
Prefix and OGA ID. ORCHIDv2 [RFC7343] decoding is selected when the
Prefix is: 2001:20::/28.
For Heirarchical HITs, the decoding is determined by the presence of
the HHIT Prefix as specified in the HHIT document.
5. ORCHID Encoding
ORCHIDv2 has a number of inputs including a Context ID, some header
bits, the hash algorithm, and the input bitstream, normally just the
public key. The output is a 96 bit value.
This addendum adds a different encoding process to that currently
used. The input to the hash function explicitly includes all the
fixed header content plus the Context ID. The fixed header content
consists of the Prefix, OGA ID, and the Additional Information.
Secondly, the length of the resulting hash is set by the rules set by
the Prefix/OGA ID. In the case of Hierarchical HITs, this is 64
bits.
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To achieve the variable length output in a consistent manner, the
cSHAKE hash is used. For this purpose, cSHAKE128 is appropriate.
The the cSHAKE function call for this addendum is:
cSHAKE128(Input, L, "", Context ID)
Input := Prefix | OGA ID | Additional Information | HOST_ID
L := Length in bits of hash portion of ORCHID
Hierarchical HIT uses the same context as all other HIPv2 HIT Suites
as they are clearly separated by the distinct HIT Suite ID.
6. Initial use case for cSHAKE
The EdDSA/cSHAKE based HITs in New Cryptographic Algorithms for HIP
[new-hip-crypto] is the first HIP Suite to use cSHAKE, thus using
this addendum.
7. Initial use case for Additional Information
Hierarchical HITs [hierarchical-hit] (HHITs) is the first HIT
construct that specifies the need of dividing the 96 bits available
to ORCHID into its Hierarchy ID (HID) and HI Hash, thus using this
addendum.
HHITs use a unique Context ID as well as a Prefix different from
HIPv2 [RFC7401]. The different Prefix enables receivers to properly
decode the HID out of the HIT and validate the HIT, given the HI.
8. Collision risks with Hierarchical HITs
The 64 bit hash size does have an increased risk of collisions over
the 96 bit hash size used for the other HIT Suites. There is a 0.01%
probability of a collision in a population of 66 million. The
probability goes up to 1% for a population of 663 million. See
Appendix A for the collision probability formula.
However, this risk of collision is within a single "Additional
Information" value. Some registration process should be used to
reject a collision, forcing the client to generate a new HI and thus
HIT and reapplying to the registration process.
9. IANA Considerations
TBD.
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10. Security Considerations
A 64 bit hash space presents a real risk of second pre-image attacks.
A Registry service effectively block attempts to "take over" such a
HIT. It does not stop a rogue attempting to impersonate a known HIT.
This attack can be mitigated by the Responder using DNS to find the
HI for the HIT or the RVS for the HIT that then provides the
registered HI.
11. References
11.1. Normative References
[NIST.FIPS.202]
Dworkin, M., "SHA-3 Standard: Permutation-Based Hash and
Extendable-Output Functions", National Institute of
Standards and Technology report,
DOI 10.6028/nist.fips.202, July 2015,
<https://doi.org/10.6028/nist.fips.202>.
[NIST.SP.800-185]
Kelsey, J., Change, S., and R. Perlner, "SHA-3 derived
functions: cSHAKE, KMAC, TupleHash and ParallelHash",
National Institute of Standards and Technology report,
DOI 10.6028/nist.sp.800-185, December 2016,
<https://doi.org/10.6028/nist.sp.800-185>.
[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>.
[RFC7343] Laganier, J. and F. Dupont, "An IPv6 Prefix for Overlay
Routable Cryptographic Hash Identifiers Version 2
(ORCHIDv2)", RFC 7343, DOI 10.17487/RFC7343, September
2014, <https://www.rfc-editor.org/info/rfc7343>.
[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
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[hierarchical-hit]
Moskowitz, R., Card, S., and A. Wiethuechter,
"Hierarchical HITs for HIPv2", Work in Progress, Internet-
Draft, draft-moskowitz-hip-hierarchical-hit-04, 3 March
2020, <https://tools.ietf.org/html/draft-moskowitz-hip-
hierarchical-hit-04>.
[Keccak] Bertoni, G., Daemen, J., Peeters, M., Van Assche, G., and
R. Van Keer, "The Keccak Function",
<https://keccak.team/index.html>.
[new-hip-crypto]
Moskowitz, R., Card, S., and A. Wiethuechter, "New
Cryptographic Algorithms for HIP", Work in Progress,
Internet-Draft, draft-moskowitz-hip-new-crypto-04, 23
January 2020, <https://tools.ietf.org/html/draft-
moskowitz-hip-new-crypto-04>.
[RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
Henderson, "Host Identity Protocol Version 2 (HIPv2)",
RFC 7401, DOI 10.17487/RFC7401, April 2015,
<https://www.rfc-editor.org/info/rfc7401>.
Appendix A. Calculating Collision Probabilities
The accepted formula for calculating the probability of a collision
is:
p = 1 - e^{-k^2/(2n)}
P Collision Probability
n Total possible population
k Actual population
Acknowledgments
Quynh Dang of NIST gave considerable guidance on using Keccak and the
NIST supporting documents. Joan Deamen of the Keccak team was
especially helpful in many aspects of using Keccak.
Authors' Addresses
Robert Moskowitz
HTT Consulting
Oak Park, MI 48237
United States of America
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Email: rgm@labs.htt-consult.com
Stuart W. Card
AX Enterprize
4947 Commercial Drive
Yorkville, NY 13495
United States of America
Email: stu.card@axenterprize.com
Adam Wiethuechter
AX Enterprize
4947 Commercial Drive
Yorkville, NY 13495
United States of America
Email: adam.wiethuechter@axenterprize.com
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