Internet DRAFT - draft-ietf-cose-hpke
draft-ietf-cose-hpke
COSE H. Tschofenig
Internet-Draft
Intended status: Standards Track O. Steele, Ed.
Expires: 24 April 2024 Transmute
D. Ajitomi
L. Lundblade
Security Theory LLC
22 October 2023
Use of Hybrid Public-Key Encryption (HPKE) with CBOR Object Signing and
Encryption (COSE)
draft-ietf-cose-hpke-07
Abstract
This specification defines hybrid public-key encryption (HPKE) for
use with CBOR Object Signing and Encryption (COSE). HPKE offers a
variant of public-key encryption of arbitrary-sized plaintexts for a
recipient public key.
HPKE works for any combination of an asymmetric key encapsulation
mechanism (KEM), key derivation function (KDF), and authenticated
encryption with additional data (AEAD) function. Authentication for
HPKE in COSE is provided by COSE-native security mechanisms or by one
of the authenticated variants of HPKE.
This document defines the use of the HPKE with COSE.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 24 April 2024.
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Copyright Notice
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document authors. All rights reserved.
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Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Without obtaining an adequate license from the person(s) controlling
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than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
3. HPKE for COSE . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1.1. Single Recipient / One Layer Structure . . . . . . . 4
3.1.2. Multiple Recipients / Two Layer Structure . . . . . . 5
3.2. Info Parameter . . . . . . . . . . . . . . . . . . . . . 7
4. Ciphersuite Registration . . . . . . . . . . . . . . . . . . 7
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Single Recipient / One Layer Example . . . . . . . . . . 10
5.2. Multiple Recipients / Two Layer . . . . . . . . . . . . . 10
5.2.1. COSE_Encrypt . . . . . . . . . . . . . . . . . . . . 11
5.2.2. COSE_MAC . . . . . . . . . . . . . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7.1. COSE Algorithms Registry . . . . . . . . . . . . . . . . 16
7.2. COSE Header Parameters . . . . . . . . . . . . . . . . . 22
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
8.1. Normative References . . . . . . . . . . . . . . . . . . 22
8.2. Informative References . . . . . . . . . . . . . . . . . 22
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Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 23
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction
Hybrid public-key encryption (HPKE) [RFC9180] is a scheme that
provides public key encryption of arbitrary-sized plaintexts given a
recipient's public key. HPKE utilizes a non-interactive ephemeral-
static Diffie-Hellman exchange to establish a shared secret. The
motivation for standardizing a public key encryption scheme is
explained in the introduction of [RFC9180].
The HPKE specification provides a variant of public key encryption of
arbitrary-sized plaintexts for a recipient public key. It also
includes three authenticated variants, including one that
authenticates possession of a pre-shared key, one that authenticates
possession of a key encapsulation mechanism (KEM) private key, and
one that authenticates possession of both a pre-shared key and a KEM
private key.
This specification utilizes HPKE as a foundational building block and
carries the output to COSE ([RFC9052], [RFC9053]).
2. Conventions and 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.
This specification uses the following abbreviations and terms:
* Content-encryption key (CEK), a term defined in CMS [RFC2630].
* Hybrid Public Key Encryption (HPKE) is defined in [RFC9180].
* pkR is the public key of the recipient, as defined in [RFC9180].
* skR is the private key of the recipient, as defined in [RFC9180].
* Key Encapsulation Mechanism (KEM), see [RFC9180].
* Key Derivation Function (KDF), see [RFC9180].
* Authenticated Encryption with Associated Data (AEAD), see
[RFC9180].
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* Additional Authenticated Data (AAD), see [RFC9180].
3. HPKE for COSE
3.1. Overview
This specification supports two uses of HPKE in COSE, namely
* HPKE in a single recipient setup. This use case utilizes a one
layer COSE structure. Section 3.1.1 provides the details.
* HPKE in a multiple recipient setup. This use case requires a two
layer COSE structure. Section 3.1.2 provides the details. While
it is possible to support the single recipient use case with a two
layer structure, the single layer setup is more efficient.
In both cases a new COSE header parameter, called 'encapsulated_key',
is used to convey the content of the enc structure defined in the
HPKE specification. "Enc" represents the serialized public key.
For use with HPKE the 'encapsulated_key' header parameter MUST be
present in the unprotected header parameter and MUST contain the
encapsulated key, which is output of the HPKE KEM, and it is a bstr.
3.1.1. Single Recipient / One Layer Structure
With the one layer structure the information carried inside the
COSE_recipient structure is embedded inside the COSE_Encrypt0.
HPKE is used to directly encrypt the plaintext and the resulting
ciphertext is either included in the COSE_Encrypt0 or is detached.
If a payload is transported separately then it is called "detached
content". A nil CBOR object is placed in the location of the
ciphertext. See Section 5 of [RFC9052] for a description of detached
payloads.
The sender MUST set the alg parameter in the protected header, which
indicates the use of HPKE.
The sender MUST place the 'encapsulated_key' parameter into the
unprotected header. Although the use of the 'kid' parameter in
COSE_Encrypt0 is discouraged by RFC 9052, this profile allows the use
of the 'kid' parameter (or other parameters) to identify the static
recipient public key used by the sender. If the COSE_Encrypt0
contains the 'kid' then the recipient may use it to select the
appropriate private key.
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HPKE defines an API and this API uses an "aad" parameter as input.
When COSE_Encrypt0 is used then there is no AEAD function executed by
COSE natively and HPKE offers this functionality.
The "aad" parameter provided to the HPKE API is constructed as
follows (and the design has been re-used from [RFC9052]):
Enc_structure = [
context : "Encrypt0",
protected : empty_or_serialized_map,
external_aad : bstr
]
empty_or_serialized_map = bstr .cbor header_map / bstr .size 0
The protected field in the Enc_structure contains the protected
attributes from the COSE_Encrypt0 structure at layer 0, encoded in a
bstr type.
The external_aad field in the Enc_structure contains the Externally
Supplied Data described in Section 4.3 and Section 5.3 in RFC 9052.
If this field is not supplied, it defaults to a zero-length byte
string.
The HPKE APIs also use an "info" parameter as input and the details
are provided in Section 3.2.
Figure 1 shows the COSE_Encrypt0 CDDL structure.
COSE_Encrypt0_Tagged = #6.16(COSE_Encrypt0)
; Layer 0
COSE_Encrypt0 = [
Headers,
ciphertext : bstr / nil,
]
Figure 1: CDDL for HPKE-based COSE_Encrypt0 Structure
The COSE_Encrypt0 MAY be tagged or untagged.
An example is shown in Section 5.1.
3.1.2. Multiple Recipients / Two Layer Structure
With the two layer structure the HPKE information is conveyed in the
COSE_recipient structure, i.e. one COSE_recipient structure per
recipient.
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In this approach the following layers are involved:
* Layer 0 (corresponding to the COSE_Encrypt structure) contains the
content (plaintext) encrypted with the CEK. This ciphertext MAY
be detached. If not detached, then it is included in the
COSE_Encrypt structure.
* Layer 1 (corresponding to a recipient structure) contains
parameters needed for HPKE to generate a shared secret used to
encrypt the CEK. This layer conveys the encrypted CEK in the
encCEK structure. The protected header MUST contain the HPKE alg
parameter and the unprotected header MUST contain the
'encapsulated_key' parameter. The unprotected header MAY contain
the kid parameter to identify the static recipient public key the
sender has been using with HPKE.
This two-layer structure is used to encrypt content that can also be
shared with multiple parties at the expense of a single additional
encryption operation. As stated above, the specification uses a CEK
to encrypt the content at layer 0.
The COSE_recipient structure, shown in Figure 2, is repeated for each
recipient.
COSE_Encrypt_Tagged = #6.96(COSE_Encrypt)
/ Layer 0 /
COSE_Encrypt = [
Headers,
ciphertext : bstr / nil,
recipients : + COSE_recipient
]
/ Layer 1 /
COSE_recipient = [
protected : bstr .cbor header_map,
unprotected : header_map,
encCEK : bstr,
]
header_map = {
Generic_Headers,
* label => values,
}
Figure 2: CDDL for HPKE-based COSE_Encrypt Structure
The COSE_Encrypt MAY be tagged or untagged.
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An example is shown in Section 5.2.
3.2. Info Parameter
The HPKE specification defines the "info" parameter as a context
information structure that is used to ensure that the derived keying
material is bound to the context of the transaction.
This section provides a suggestion for constructing the info
structure. HPKE leaves the info parameter for these two functions as
optional. Application profiles of this specification MAY populate
the fields of the COSE_KDF_Context structure or MAY use a different
structure as input to the "info" parameter. If no content for the
"info" parameter is not supplied, it defaults to a zero-length byte
string.
This specification re-uses the context information structure defined
in [RFC9053] as a foundation for the info structure. This payload
becomes the content of the info parameter for the HPKE functions,
when utilized. For better readability of this specification the
COSE_KDF_Context structure is repeated in Figure 3.
PartyInfo = (
identity : bstr / nil,
nonce : bstr / int / nil,
other : bstr / nil
)
COSE_KDF_Context = [
AlgorithmID : int / tstr,
PartyUInfo : [ PartyInfo ],
PartyVInfo : [ PartyInfo ],
SuppPubInfo : [
keyDataLength : uint,
protected : empty_or_serialized_map,
? other : bstr
],
? SuppPrivInfo : bstr
]
Figure 3: COSE_KDF_Context Data Structure as 'info' Parameter for
HPKE
4. Ciphersuite Registration
This specification registers a number of ciphersuites for use with
HPKE. A ciphersuite is thereby a combination of several algorithm
configurations:
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* HPKE Mode
* KEM algorithm
* KDF algorithm
* AEAD algorithm
The "KEM", "KDF", and "AEAD" values are conceptually taken from the
HPKE IANA registry [HPKE-IANA]. Hence, COSE-HPKE cannot use a
algorithm combination that is not already available with HPKE.
For better readability of the algorithm combination ciphersuites
labels are build according to the following scheme:
HPKE-<Version>-<Mode>-<KEM>-<KDF>-<AEAD>
The "Mode" indicator may be populated with the following values from
Table 1 of [RFC9180]:
* "Base" refers to "mode_base" described in Section 5.1.1 of
[RFC9180], which only enables encryption to the holder of a given
KEM private key.
* "PSK" refers to "mode_psk", described in Section 5.1.2 of
[RFC9180], which authenticates using a pre-shared key.
* "Auth" refers to "mode_auth", described in Section 5.1.3 of
[RFC9180], which authenticates using an asymmetric key.
* "Auth_Psk" refers to "mode_auth_psk", described in Section 5.1.4
of [RFC9180], which authenticates using both a PSK and an
asymmetric key.
For a list of ciphersuite registrations, please see Section 7. The
following table summarizes the relationship between the ciphersuites
registered in this document and the values registered in the HPKE
IANA registry [HPKE-IANA].
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+--------------------------------------------------+------------------+
| COSE-HPKE | HPKE |
| Cipher Suite Label | KEM | KDF | AEAD |
+--------------------------------------------------+-----+-----+------+
| HPKE-Base-P256-SHA256-AES128GCM |0x10 | 0x1 | 0x1 |
| HPKE-Base-P256-SHA256-ChaCha20Poly1305 |0x10 | 0x1 | 0x3 |
| HPKE-Base-P384-SHA384-AES256GCM |0x11 | 0x2 | 0x2 |
| HPKE-Base-P384-SHA384-ChaCha20Poly1305 |0x11 | 0x2 | 0x3 |
| HPKE-Base-P521-SHA512-AES256GCM |0x12 | 0x3 | 0x2 |
| HPKE-Base-P521-SHA512-ChaCha20Poly1305 |0x12 | 0x3 | 0x3 |
| HPKE-Base-X25519-SHA256-AES128GCM |0x20 | 0x1 | 0x1 |
| HPKE-Base-X25519-SHA256-ChaCha20Poly1305 |0x20 | 0x1 | 0x3 |
| HPKE-Base-X448-SHA512-AES256GCM |0x21 | 0x3 | 0x2 |
| HPKE-Base-X448-SHA512-ChaCha20Poly1305 |0x21 | 0x3 | 0x3 |
| HPKE-Base-X25519Kyber768-SHA256-AES256GCM |0x30 | 0x1 | 0x2 |
| HPKE-Base-X25519Kyber768-SHA256-ChaCha20Poly1305 |0x30 | 0x1 | 0x3 |
| HPKE-Base-CP256-SHA256-ChaCha20Poly1305 |0x13 | 0x1 | 0x3 |
| HPKE-Base-CP256-SHA256-AES128GCM |0x13 | 0x1 | 0x1 |
| HPKE-Base-CP521-SHA512-ChaCha20Poly1305 |0x15 | 0x3 | 0x3 |
| HPKE-Base-CP521-SHA512-AES256GCM |0x15 | 0x3 | 0x2 |
+--------------------------------------------------+-----+-----+------+
Note that the last four entries in the table refer to the compact
encoding of the public keys defined in [I-D.irtf-cfrg-dnhpke].
As the list indicates, the ciphersuite labels have been abbreviated
at least to some extend to maintain the tradeoff between readability
and length.
5. Examples
This section provides a set of examples that shows all COSE message
types (COSE_Encrypt0, COSE_Encrypt and COSE_MAC) to which the COSE-
HPKE can be applied. Each example includes the following information
that can be used to check the interoperability of COSE-HPKE
implementations:
* plaintext: Original data of the encrypted payload.
* external_aad: Externally supplied AAD.
* skR: A recipient private key.
* skE: An ephemeral sender private key paired with the
encapsulated_key.
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5.1. Single Recipient / One Layer Example
This example assumes that a sender wants to communicate an encrypted
payload to a single recipient in the most efficient way.
An example of the COSE_Encrypt0 structure using the HPKE scheme is
shown in Figure 4. Line breaks and comments have been inserted for
better readability.
This example uses the following:
* alg: HPKE-Base-P256-SHA256-AES128GCM
* plaintext: "This is the content."
* external_aad: "COSE-HPKE app"
* skR: h'57c92077664146e876760c9520d054aa93c3afb04e306705db609030850
7b4d3'
* skE: h'42dd125eefc409c3b57366e721a40043fb5a58e346d51c133128a772371
60218'
16([
/ alg = HPKE-Base-P256-SHA256-AES128GCM (Assumed: 35) /
h'a1011823',
{
/ kid /
4: h'3031',
/ encapsulated_key /
-4: h'045df24272faf43849530db6be01f42708b3c3a9
df8e268513f0a996ed09ba7840894a3fb946cb28
23f609c59463093d8815a7400233b75ca8ecb177
54d241973e',
},
/ encrypted plaintext /
h'35aa3d98739289b83751125abe44e3b977e4b9abbf2c8cfaade
b15f7681eef76df88f096',
])
Figure 4: COSE_Encrypt0 Example for HPKE
5.2. Multiple Recipients / Two Layer
In this example we assume that a sender wants to transmit a payload
to two recipients using the two-layer structure. Note that it is
possible to send two single-layer payloads, although it will be less
efficient.
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5.2.1. COSE_Encrypt
An example of the COSE_Encrypt structure using the HPKE scheme is
shown in Figure 5. Line breaks and comments have been inserted for
better readability.
This example uses the following:
* Encryption alg: AES-128-GCM
* plaintext: "This is the content."
* detatched ciphertext: h'cc168c4e148c52a83010a75250935a47ccb8682dee
bcef8fce5d60c161e849f53a2dc664'
* kid:"01"
- alg: HPKE-Base-P256-SHA256-AES128GCM
- external_aad: "COSE-HPKE app"
- skR: h'57c92077664146e876760c9520d054aa93c3afb04e306705db609030
8507b4d3'
- skE: h'97ad883f949f4cdcb1301b9446950efd4eb519e16c4a3d78304eec83
2692f9f6'
* kid:"02"
- alg: HPKE-Base-X25519-SHA256-CHACHA20POLY1305
- external_aad: "COSE-HPKE app"
- skR: h'bec275a17e4d362d0819dc0695d89a73be6bf94b66ab726ae0b1afe3
c43f41ce'
- skE: h'b8ed3f4df56c230e36fa6620a47f24d08856d242ea547c5521ff7bd6
9af8fd6f'
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96_0([
/ alg = AES-128-GCM (1) /
h'a10101',
{
/ iv /
5: h'b3fb95dde18c6f90a9f0ae55',
},
/ detached ciphertext /
null,
[
[
/ alg = HPKE-Base-P256-SHA256-AES128GCM (Assumed: 35) /
h'a1011823',
{
/ kid /
4: h'3031',
/ encapsulated_key /
-4: h'04d97b79486fe2e7b98fb1bd43
c4faee316ff38d28609a1cf568
40a809298a91e601f1cc0c2ba4
6cb67b41f4651b769cafd9df78
e58aa7f5771291bd4f0f420ba6',
},
/ ciphertext containing encrypted CEK /
h'24450f54ae93375351467d17aa7a795cfede2
c03eced1ad21fcb7e7c2fe64397',
],
[
/ alg = HPKE-Base-X25519-SHA256-CHACHA20POLY1305 (Assumed: 42) /
h'a101182a',
{
/ kid /
4: h'3032',
/ encapsulated_key /
-4: h'd1afbdc95b0e735676f6bca34f
be50f2822259ac09bfc3c500f1
4a05de9b2833',
},
/ ciphertext containing encrypted CEK /
h'079b443ec6dfcda6a5f8748aff3875146a8ed
40359e1279b545166385d8d9b59',
],
],
])
Figure 5: COSE_Encrypt Example for HPKE
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To offer authentication of the sender the payload in Figure 5 is
signed with a COSE_Sign1 wrapper, which is outlined in Figure 6. The
payload in Figure 6 is meant to contain the content of Figure 5.
18(
[
/ protected / h'a10126' / {
\ alg \ 1:-7 \ ECDSA 256 \
} / ,
/ unprotected / {
/ kid / 4:'sender@example.com'
},
/ payload / h'AA19...B80C',
/ signature / h'E3B8...25B8'
]
)
Figure 6: COSE_Encrypt Example for HPKE
5.2.2. COSE_MAC
An example of the COSE_MAC structure using the HPKE scheme is shown
in Figure 7.
This example uses the following:
* MAC alg: HMAC 256/256
* payload: "This is the content."
* kid:"01"
- alg: HPKE-Base-P256-SHA256-AES128GCM
- external_aad: "COSE-HPKE app"
- skR: h'57c92077664146e876760c9520d054aa93c3afb04e306705db609030
8507b4d3'
- skE: h'e5dd9472b5807636c95be0ba2575020ba91cbb3561b52be141da8967
8c664307'
* kid:"02"
- alg: HPKE-Base-X25519-SHA256-CHACHA20POLY1305
- external_aad: "COSE-HPKE app"
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- skR: h'bec275a17e4d362d0819dc0695d89a73be6bf94b66ab726ae0b1afe3
c43f41ce'
- skE: h'78a49d7af71b5244498e943f361aa0250184afc48b8098a68ae97ccd
2cd7e56f'
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97_0([
/ alg = HMAC 256/256 (5) /
h'a10105',
{},
/ payload = 'This is the content.' /
h'546869732069732074686520636f6e74656e742e',
/ tag /
h'5cdcf6055fcbdb53b4001d8fb88b2a46b200ed28e1ed77e16ddf43fb3cac3a98',
[
[
/ alg = HPKE-Base-P256-SHA256-AES128GCM (Assumed: 35) /
h'a1011823',
{
/ kid = '01' /
4: h'3031',
/ encapsulated_key /
-4: h'043ac21632e45e1fbd733f002a
621aa4f3d94737adc395d5a7cb
6e9554bd1ad273aec991493786
d72616d9759bf8526e6e20c1ed
c41ba5739f2b2e441781aa0eb4',
},
/ ciphertext containing encrypted MAC key /
h'5cee2b4235a7ff695164f7a8d1e79ccf3ca3d
e8b22f3592626020a95b2a8d3fb4d7aa7fe37
432426ee70073a368f29d1',
],
[
/ alg = HPKE-Base-X25519-SHA256-CHACHA20POLY1305 (Assumed: 42) /
h'a101182a',
{
/ kid = '02' /
4: h'3032',
/ encapsulated_key /
-4: h'02cffacc60def3bb3d0a1c3661
227c9de8dc2b1d3939dd2c07d4
49ebb0bba324',
},
/ ciphertext containing encrypted MAC key /
h'3f5b8b60271d5234dbea554dc1461d0239e9f
4589f6415e8563b061dbcb37795a616111b78
2b4c589b534309327ffadc',
],
],
])
Figure 7: COSE_MAC Example for HPKE
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6. Security Considerations
This specification is based on HPKE and the security considerations
of [RFC9180] are therefore applicable also to this specification.
HPKE assumes the sender is in possession of the public key of the
recipient and HPKE COSE makes the same assumptions. Hence, some form
of public key distribution mechanism is assumed to exist but outside
the scope of this document.
HPKE relies on a source of randomness to be available on the device.
Additionally, with the two layer structure the CEK is randomly
generated and it MUST be ensured that the guidelines in [RFC8937] for
random number generations are followed.
HPKE in Base mode does not offer authentication as part of the HPKE
KEM. In this case COSE constructs like COSE_Sign, COSE_Sign1,
COSE_MAC, or COSE_MAC0 can be used to add authentication. HPKE also
offers modes that offer authentication.
If COSE_Encrypt or COSE_Encrypt0 is used with a detached ciphertext
then the subsequently applied integrity protection via COSE_Sign,
COSE_Sign1, COSE_MAC, or COSE_MAC0 does not cover this detached
ciphertext. Implementers MUST ensure that the detached ciphertext
also experiences integrity protection. This is, for example, the
case when an AEAD cipher is used to produce the detached ciphertext
but may not be guaranteed by non-AEAD ciphers.
7. IANA Considerations
This document requests IANA to add new values to the 'COSE
Algorithms' and to the 'COSE Header Parameters' registries.
7.1. COSE Algorithms Registry
* Name: HPKE-Base-P256-SHA256-AES128GCM
* Value: TBD1 (Assumed: 35)
* Description: Cipher suite for COSE-HPKE in Base Mode that uses the
DHKEM(P-256, HKDF-SHA256) KEM, the HKDF-SHA256 KDF and the AES-
128-GCM AEAD.
* Capabilities: [kty]
* Change Controller: IESG
* Reference: [[TBD: This RFC]]
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* Recommended: Yes
* Name: HPKE-Base-P256-SHA256-ChaCha20Poly1305
* Value: TBD2 (Assumed: 36)
* Description: Cipher suite for COSE-HPKE in Base Mode that uses the
DHKEM(P-256, HKDF-SHA256) KEM, the HKDF-SHA256 KDF and the
ChaCha20Poly1305 AEAD.
* Capabilities: [kty]
* Change Controller: IESG
* Reference: [[TBD: This RFC]]
* Recommended: Yes
* Name: HPKE-Base-P384-SHA384-AES256GCM
* Value: TBD3 (Assumed: 37)
* Description: Cipher suite for COSE-HPKE in Base Mode that uses the
DHKEM(P-384, HKDF-SHA384) KEM, the HKDF-SHA384 KDF, and the AES-
256-GCM AEAD.
* Capabilities: [kty]
* Change Controller: IESG
* Reference: [[TBD: This RFC]]
* Recommended: Yes
* Name: HPKE-Base-P384-SHA384-ChaCha20Poly1305
* Value: TBD4 (Assumed: 38)
* Description: Cipher suite for COSE-HPKE in Base Mode that uses the
DHKEM(P-384, HKDF-SHA384) KEM, the HKDF-SHA384 KDF, and the
ChaCha20Poly1305 AEAD.
* Capabilities: [kty]
* Change Controller: IESG
* Reference: [[TBD: This RFC]]
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* Recommended: Yes
* Name: HPKE-Base-P521-SHA512-AES256GCM
* Value: TBD5 (Assumed: 39)
* Description: Cipher suite for COSE-HPKE in Base Mode that uses the
DHKEM(P-521, HKDF-SHA512) KEM, the HKDF-SHA512 KDF, and the AES-
256-GCM AEAD.
* Capabilities: [kty]
* Change Controller: IESG
* Reference: [[TBD: This RFC]]
* Recommended: Yes
* Name: HPKE-Base-P521-SHA512-ChaCha20Poly1305
* Value: TBD6 (Assumed: 40)
* Description: Cipher suite for COSE-HPKE in Base Mode that uses the
DHKEM(P-521, HKDF-SHA512) KEM, the HKDF-SHA512 KDF, and the
ChaCha20Poly1305 AEAD.
* Capabilities: [kty]
* Change Controller: IESG
* Reference: [[TBD: This RFC]]
* Recommended: Yes
* Name: HPKE-Base-X25519-SHA256-AES128GCM
* Value: TBD7 (Assumed: 41)
* Description: Cipher suite for COSE-HPKE in Base Mode that uses the
DHKEM(X25519, HKDF-SHA256) KEM, the HKDF-SHA256 KDF, and the AES-
128-GCM AEAD.
* Capabilities: [kty]
* Change Controller: IESG
* Reference: [[TBD: This RFC]]
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* Recommended: Yes
* Name: HPKE-Base-X25519-SHA256-ChaCha20Poly1305
* Value: TBD8 (Assumed: 42)
* Description: Cipher suite for COSE-HPKE in Base Mode that uses the
DHKEM(X25519, HKDF-SHA256) KEM, the HKDF-SHA256 KDF, and the
ChaCha20Poly1305 AEAD.
* Capabilities: [kty]
* Change Controller: IESG
* Reference: [[TBD: This RFC]]
* Recommended: Yes
* Name: HPKE-Base-X448-SHA512-AES256GCM
* Value: TBD9 (Assumed: 43)
* Description: Cipher suite for COSE-HPKE in Base Mode that uses the
DHKEM(X448, HKDF-SHA512) KEM, the HKDF-SHA512 KDF, and the AES-
256-GCM AEAD.
* Capabilities: [kty]
* Change Controller: IESG
* Reference: [[TBD: This RFC]]
* Recommended: Yes
* Name: HPKE-Base-X448-SHA512-ChaCha20Poly1305
* Value: TBD10 (Assumed: 44)
* Description: Cipher suite for COSE-HPKE in Base Mode that uses the
DHKEM(X448, HKDF-SHA512) KEM, the HKDF-SHA512 KDF, and the
ChaCha20Poly1305 AEAD.
* Capabilities: [kty]
* Change Controller: IESG
* Reference: [[TBD: This RFC]]
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* Recommended: Yes
* Name: HPKE-Base-X25519Kyber768-SHA256-AES256GCM
* Value: TBD11 (Assumed: 250)
* Description: Cipher suite for COSE-HPKE in Base Mode that uses the
X25519Kyber768Draft00 KEM, the HKDF-SHA256 KDF, and the AES-
256-GCM AEAD.
* Capabilities: [kty]
* Change Controller: IESG
* Reference: [[TBD: This RFC]]
* Recommended: No
* Name: HPKE-Base-X25519Kyber768-SHA256-ChaCha20Poly1305
* Value: TBD12 (Assumed: 251)
* Description: Cipher suite for COSE-HPKE in Base Mode that uses the
X25519Kyber768Draft00 KEM, the HKDF-SHA256 KDF, and the
ChaCha20Poly1305 AEAD.
* Capabilities: [kty]
* Change Controller: IESG
* Reference: [[TBD: This RFC]]
* Recommended: No
* Name: HPKE-Base-CP256-SHA256-ChaCha20Poly1305
* Value: TBD13 (Assumed: 45)
* Description: Cipher suite for COSE-HPKE in Base Mode that uses the
DHKEM(CP-256, HKDF-SHA256) KEM, the HKDF-SHA256 KDF and the
ChaCha20Poly1305 AEAD.
* Capabilities: [kty]
* Change Controller: IESG
* Reference: [[TBD: This RFC]]
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* Recommended: Yes
* Name: HPKE-Base-CP521-SHA512-ChaCha20Poly1305
* Value: TBD14 (Assumed: 46)
* Description: Cipher suite for COSE-HPKE in Base Mode that uses the
DHKEM(CP-521, HKDF-SHA512) KEM, the HKDF-SHA512 KDF, and the
ChaCha20Poly1305 AEAD.
* Capabilities: [kty]
* Change Controller: IESG
* Reference: [[TBD: This RFC]]
* Recommended: Yes
* Name: HPKE-Base-CP256-SHA256-AES128GCM
* Value: TBD15 (Assumed: 47)
* Description: Cipher suite for COSE-HPKE in Base Mode that uses the
DHKEM(CP-256, HKDF-SHA256) KEM, the HKDF-SHA256 KDF and the
AES128GCM AEAD.
* Capabilities: [kty]
* Change Controller: IESG
* Reference: [[TBD: This RFC]]
* Recommended: Yes
* Name: HPKE-Base-CP521-SHA512-AES256GCM
* Value: TBD16 (Assumed: 47)
* Description: Cipher suite for COSE-HPKE in Base Mode that uses the
DHKEM(CP-521, HKDF-SHA512) KEM, the HKDF-SHA512 KDF, and the
AES256GCM AEAD.
* Capabilities: [kty]
* Change Controller: IESG
* Reference: [[TBD: This RFC]]
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* Recommended: Yes
7.2. COSE Header Parameters
* Name: encapsulated_key
* Label: TBDX (Assumed: -4)
* Value type: bstr
* Value Registry: N/A
* Description: HPKE encapsulated key
* Reference: [[This specification]]
8. References
8.1. 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/rfc/rfc2119>.
[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/rfc/rfc8174>.
[RFC9052] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", STD 96, RFC 9052,
DOI 10.17487/RFC9052, August 2022,
<https://www.rfc-editor.org/rfc/rfc9052>.
[RFC9053] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053,
August 2022, <https://www.rfc-editor.org/rfc/rfc9053>.
[RFC9180] Barnes, R., Bhargavan, K., Lipp, B., and C. Wood, "Hybrid
Public Key Encryption", RFC 9180, DOI 10.17487/RFC9180,
February 2022, <https://www.rfc-editor.org/rfc/rfc9180>.
8.2. Informative References
[HPKE-IANA]
IANA, "Hybrid Public Key Encryption (HPKE) IANA Registry",
October 2023,
<https://www.iana.org/assignments/hpke/hpke.xhtml>.
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[I-D.irtf-cfrg-dnhpke]
Harkins, D., "Deterministic Nonce-less Hybrid Public Key
Encryption", Work in Progress, Internet-Draft, draft-irtf-
cfrg-dnhpke-03, 19 October 2023,
<https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-
dnhpke-03>.
[RFC2630] Housley, R., "Cryptographic Message Syntax", RFC 2630,
DOI 10.17487/RFC2630, June 1999,
<https://www.rfc-editor.org/rfc/rfc2630>.
[RFC8937] Cremers, C., Garratt, L., Smyshlyaev, S., Sullivan, N.,
and C. Wood, "Randomness Improvements for Security
Protocols", RFC 8937, DOI 10.17487/RFC8937, October 2020,
<https://www.rfc-editor.org/rfc/rfc8937>.
Appendix A. Contributors
We would like thank the following individuals for their contributions
to the design of embedding the HPKE output into the COSE structure
following a long and lively mailing list discussion:
* Richard Barnes
* Ilari Liusvaara
Finally, we would like to thank Russ Housley and Brendan Moran for
their contributions to the draft as co-authors of initial versions.
Appendix B. Acknowledgements
We would like to thank John Mattsson, Mike Prorock, Michael
Richardson, and Goeran Selander for their review feedback.
Authors' Addresses
Hannes Tschofenig
Austria
Email: hannes.tschofenig@gmx.net
Orie Steele (editor)
Transmute
United States
Email: orie@transmute.industries
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Daisuke Ajitomi
Japan
Email: dajiaji@gmail.com
Laurence Lundblade
Security Theory LLC
United States
Email: lgl@securitytheory.com
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