New Cryptographic Algorithms for HIPHTT ConsultingOak ParkMI48237USArgm@labs.htt-consult.comAX Enterprize4947 Commercial DriveYorkvilleNY13495USAstu.card@axenterprize.comAX Enterprize4947 Commercial DriveYorkvilleNY13495USAadam.wiethuechter@axenterprize.com
Internet
HIPRFCRequest for CommentsI-DInternet-DraftHIP
This document provides new cryptographic algorithms to be used with
HIP. The Edwards Elliptic Curve and the Keccak sponge functions
are the main focus. The HIP parameters and processing instructions
impacted by these algorithms are defined.
This document adds new cryptographic algorithms for HIPv2. This includes:
New elliptic curves for ECDH.
The Edwards Elliptic Curve Digital Signature Algorithm (EdDSA)
used in Host Identities (HI) and for Base Exchange (BEX)
signatures.
Hashes used in Host Identity Tag (HIT) generation, and
wherever else hashes are needed.
Keyed hashes used for KEYMAT generation and packet MACing
operations.
AEAD and stream ciphers to use in HIP and HIP enabled secure
communication protocols.
The hashes and encryption are all built on the Keccak sponge function.
These additions reflect selection of advances in the field of
cryptography that would best benefit HIP, particularly in
constrained devices and communications.
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 when, and only when, they appear in all
capitals, as shown here.
`
The family of all sponge functions with a KECCAK-f
permutation as the underlying function and multi-rate
padding as the padding rule.
A PRF and keyed hash function based on KECCAK.
Extends the SHAKE scheme to allow users to customize their
use of the function.
A secure hash that allows for an arbitrary output length.
A function that can be used to generate output from a
random seed such that the output is computationally
indistinguishable from truly random output.
In the sponge construction, the width of the underlying
function minus the rate.
In the sponge construction, the number of input bits
processed per invocation of the underlying function.
A function on bit strings (also called messages) in which
the output can be extended to any desired length.
HIP parameters carry information that is necessary for establishing
and maintaining a HIP association. For example, the device's
public keys as well as the signaling for negotiating ciphers and
payload handling are encapsulated in HIP parameters. Additional
information, meaningful for end hosts or middleboxes, may also be
included in HIP parameters. The specification of the HIP
parameters and their mapping to HIP packets and packet types is
flexible to allow HIP extensions to define new parameters and new
protocol behavior.
Elliptic curves Curve25519 and Curve448 RFC
7748) are specified here for use in the HIP Diffie-Hellman
exchange.
Curve25519 and Curve448 are already defined in Section 5.2.1 of
, using the HIP-DEX CKDF.
Here they are defined for using the new KMAC NIST SP 800-185 derived KDF in
.
The DIFFIE_HELLMAN parameter may be included in selected HIP
packets based on the DH Group ID selected. The DIFFIE_HELLMAN
parameter is defined in Section 5.2.7 of .
The following Elliptic Curves are defined here:
A new KDF for KEYMAT, Section 6.5 of and
Section 6.3 of using
Keccak is defined in .
Edwards-Curve Digital Signature Algorithm (EdDSA) (RFC 8032) are specified here for use as
Host Identities (HIs).
The HOST_ID parameter specifies the public key algorithm, and for
elliptic curves, a name. The HOST_ID parameter is defined in
Section 5.2.19 of .
For hosts that implement EdDSA as the algorithm, the following ECC
curves are available:
The HIT_SUITE_LIST parameter contains a list of the supported
HIT suite IDs of the Responder. Based on the HIT_SUITE_LIST,
the Initiator can determine which source HIT Suite IDs are
supported by the Responder. The HIT_SUITE_LIST parameter is
defined in Section 5.2.10 of .
The following HIT Suite ID is defined, and the relationship
between the four-bit ID value used in the OGA ID field and the
eight-bit encoding within the HIT_SUITE_LIST ID field is
clarified:
The following table provides more detail on the above HIT Suite
combinations. The input for each generation algorithm is the
encoding of the HI as defined in . The
output is 96 bits long and is directly used in the ORCHID.
IndexHash functionHMACSignature algorithm familyDescription5SHAKE128KMAC128EdDSAEdDSA HI hashed with cSHAKE128, output is 96 bits
The Keccak sponge function is the
basis for the new SHA-3, standard NIST
FIPS 202, and the customized XOF functions in NIST SP 800-185. These are used
here as an alternative to all the hashing functions in HIP.
Hardware implementation of Keccak in VHDL is available from Keccak.
Keccak is described as a sponge function. The analogy to a
sponge is that an arbitrary number of input bits are "absorbed"
into the state of the function, after which an arbitrary number of
output bits are "squeezed" out of its state.
The Keccak function is defined to have a width of b bits.
Where b is the capacity (c) + rate (r).
The rate is the number of bits "fed" into the sponge at a time.
The capacity is twice the desired hash "strength" and part of the
sponge width.
b is one of the set {25, 50, 100, 200, 400, 800, 1600}. In FIPS
202, b=1600. Thus a hash strength of 128 bits can be delivered
with c=256 and r=1344, or 168 byte segment input to the sponge.
Keccak can also provide a hash strength of 128 bit with b=800
(r=544 or 68 bytes) and b=400 (r=144 or 18 bytes). 256 bit
strength can only be provided with b=1600 or 800.
FIPS 202 does not specify use of these smaller values for b which
may be preferred in memory constrained devices, processing
relatively short input strings. Future work will determine if the
smaller values for b result in a significant performance/memory
improvement to warrant their use.
The RHASH is the general term used throughout to refer to the hash used for a specific HIT
suite. For this addendum SHAKE128 is used, even for HIs of
EdDSA448.
Unless otherwise specified, L of SHAKE128 is 256, resulting in a
similar output to SHA256. Any truncation used for, older, fixed
output hashes is still used. This is to simplify code
integration. One exception to this is in .
The HIP_MAC and HIP_MAC2 parameters in
use HMAC . This performs two hashes on a
string with a key for a keyed hash the length of the underlying hash.
Here, KMAC from NIST SP
800-185 is used. This is a single pass using the underlying
cSHAKE function. The function call is:
HIP encrypted parameters use the HIP_CIPHER, Section 5.2.8 of . The Keccak Keyak cipher, , is recommended.
Keyak is a candidate in the NIST Lightweight Cryptography
competition and is consistent with the overall approach in this
addendum to use Keccak functions for simplicity in design and
implementation.
The HIP_CIPHER parameter values for Keyak are:
For use as the HIP Cipher, the TAG generated in Keyak is length 0.
The Keyak SUV is the key plus IV specified for the encrypted
parameter. River Keyak MAY be used for , in place of AES-CTR.
Lake Keyak can provide 256 bits of security by following the
recommendations for the Keyak cipher.
The EdDSA/cSHAKE based HITs vary slightly the ORCHID generation
method described in section 3.2 of . The
XOF functionality of cSHAKE produces an output of L bits. This
replaces the Encode_96 function in the ORCHID generation.
For identities that are EdDSA public keys, the ORCHID input
consists of the public key encoding as specified for the Host
Identity field of the HOST_ID parameter (see ). Since L is less than 128, cSHAKE128 is used
for all EdDSA curve sizes:
The KMAC function provides a new, more efficient, key derivation
function over HKDF . This will be
referred to as KKDF.
The choice of KMAC128 or KMAC256 is based on the strength of the
output key material. For 256 bits of strength equivalent to
HMAC-SHA256, use KMAC256. Per NIST SP 800-56Cr1, Section 4.1,
Option 3:
L is the derived key bit length. Since 4 HIP keys are "drawn" from
this output, the length is 4 * HIP_key_size. Per ASIACRYPT 2017, pp. 606-637 each of
these derived keys will have the same strength as the
Diffie-Hellman shared secret.
S is the byte string 01001011 || 01000100 || 01000110, which
represents the sequence of characters “K”, “D”, and “F” in 8-bit
ASCII.
Salt and info are derived as defined in
or . There are special
security considerations for IKM per . The
two HIs MUST be used in constructing IKM as follows:
These are separately DER encoded.
Appendix B of NIST SP 800-185
defines how to use SHAKE, cSHAKE, or KMAC as a PRF.
IANA will need to make the following changes to the "Host
Identity Protocol (HIP) Parameters" registries:
This document defines the new Curve25519 and Curve448 for the
Diffie-Hellman exchange (see ).
This document defines the new EdDSA Host ID (see ).
This document defines the new HIT Suite of EdDSA/cSHAKE (see
).
This document defines the new Keyak ciphers for HIP encrypted
parameters (see ).
warns about using Curve25519 and Curve448
in Diffie-Hellman for key derivation:
Designers using these curves should be aware that for each public
key, there are several publicly computable public keys that are
equivalent to it, i.e., they produce the same shared secrets. Thus
using a public key as an identifier and knowledge of a shared
secret as proof of ownership (without including the public keys in
the key derivation) might lead to subtle vulnerabilities.
This applies to , but may
have broader consequences. Thus the two Host IDs are included with
the Diffie-Hellman secret.
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, particularly
with the KEYMAT section and the strength of the derived keys.
Full-State Keyed Duplex with Built-In Multi-user SupportThe Keccak FunctionRadboud UniversitySTMicroelectronicsSTMicroelectronicsSTMicroelectronicsThe Keyak CipherRadboud UniversitySTMicroelectronicsSTMicroelectronicsSTMicroelectronics