Use of Hybrid Public-Key Encryption (HPKE) with Javascript Object Signing and Encryption (JOSE)

Internet-Draft	Use of HPKE in JOSE	February 2024
Reddy, et al.	Expires 8 August 2024	[Page]

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This Internet-Draft will expire on 8 August 2024.¶

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This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶

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 JOSE ([RFC7516], [RFC7518]).¶

2. Conventions and Definitions

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.¶

3. Conventions and Terminology

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].¶
Additional Authenticated Data (AAD), see [RFC9180].¶
Key Type (kty), see [RFC7517].¶

4. HPKE for JOSE

4.1. Overview

The JSON Web Algorithms (JWA) [RFC7518] in Section 4.6 defines two ways using the key agreement result (a) Direct Key Agreement (b) Key Agreement with Key Wrapping.¶

This specification supports two uses of HPKE in JOSE, namely¶

HPKE in a single recipient setup referred to as Integrated Encryption mode. In this case, the shared secret established through the HPKE will generate the content encryption key (CEK) and encrypts the plaintext.¶
HPKE in a multiple recipient setup referred to as Key Encryption mode. In this case, the shared secret established through the HPKE will wrap the CEK.¶

In both modes, the existing JOSE header parameter, called 'epk', is used to convey the content of the "encapsulated key" structure defined in the HPKE specification. The "encapsulated key" structure represents the serialized form of a public key.¶

When the alg value is set to any of algorithms registered by this specification then the 'epk' header parameter MUST be present, and it MUST be a JSON Web Key as defined in Section 4.4 of this document.¶

In both modes, the header parameter 'epk' will contain the 'ek' member. The "ek" member will contain the base64url encoded "enc" value produced by the encapsulate operation of the HPKE KEM.¶

In both JWE Compact Serialization and the JWE JSON Serialization, "ct" and "enc" will be base64url encoded (see Section 7.1 and 7.2 of [RFC7518]), since JSON lacks a way to directly represent arbitrary octet sequences.¶

The two modes (Integrated Encryption, and Key Encryption) can be distinguished by determining whether an "enc" member is present in the protected header.¶

If the "enc" member exists, it is a Key Encryption mode; otherwise, it is a Integrated Encryption mode.¶

4.2. HPKE Encryption with SealBase

The message encryption process is as follows.¶

The sending HPKE context is created by invoking invoking SetupBaseS() (Section 5.1.1 of [RFC9180]) with the recipient's public key "pkR" and "info". 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. The SetupBaseS function will be called with the default value of an empty string for the 'info' parameter. This yields the context "sctxt" and an encapsulation key "enc".¶
If "zip" parameter is present, compression is applied to the plaintext "pt" using the specified compression algorithm. Encrypt plaintext "pt" by invoking the Seal() method (Section 5.2 of [RFC9180]) on "sctxt" with "aad", yielding ciphertext "ct".¶

Two cases of plaintext need to be distinguished:¶
- In Integrated Encryption mode, the plaintext "pt" passed into Seal is the content to be encrypted. Hence, there is no intermediate layer utilizing a CEK.¶
- In Key Encryption mode, the plaintext "pt" passed into Seal is the CEK. The CEK is a random byte sequence of length appropriate for the encryption algorithm. For example, AES-128-GCM requires a 16 byte key and the CEK would therefore be 16 bytes long.¶

4.3. HPKE Decryption with OpenBase

The recipient will create the receiving HPKE context by invoking SetupBaseR() (Section 5.1.1 of [RFC9180]) with "skR", "enc" (output of base64url decoded 'ek'), and "info" (empty string). This yields the context "rctxt". The receiver then decrypts "ct" by invoking the Open() method on "rctxt" (Section 5.2 of [RFC9180]) with "aad", yielding "pt" or an error on failure.¶

The Open function will, if successful, decrypts "ct". When decrypted, the result will be either the CEK (when Key Encryption mode is used), or the content (if Integrated Encryption mode is used). The CEK is the symmetric key used to decrypt the ciphertext. If a "zip" parameter was included, the recipient will uncompress the decrypted plaintext using the specified compression algorithm.¶

4.4. Encapsulated JSON Web Keys

An encapsulated key can be represented as JSON Web Key as described in { Section 4 of RFC7515 }.¶

The "kty" parameter MUST be "EK".¶

The "ek" parameter MUST be present, and MUST be the base64url encoded output of the encap operation defined for the HPKE KEM.¶

As described in { Section 4 of RFC7515 }, additional members can be present in the JWK; if not understood by implementations encountering them, they MUST be ignored.¶

This example demonstrates the representaton of an encapsulated key as a JWK.¶

{
   "kty": "EK",
   "ek": "BHpP-u5JKziyUpqxNQqb0apHx1ecH2UzcRlhHR4ngJVS__gNu21DqqgPweuPpjglnXDnOuQ4kt9tHCs3PUzPxQs"
}

4.4.1. Integrated Encryption

In Integrated Encryption mode, HPKE is employed to directly encrypt the (compressed) plaintext, and the resulting ciphertext is included in the JWE ciphertext.¶

In this mode, JWE Compact serialization MUST be used. The sender MUST specify the 'epk' and 'alg' parameters in the protected header to indicate the use of HPKE. Optionally, the protected header MAY contain the 'kid' parameter used to identify the static recipient public key used by the sender.¶

The Single-Shot APIs specified in Section 6 of [RFC9180] for encryption and decryption cannot be used. This is because they require an 'aad' parameter, which takes the Encoded Protected Header comprising of 'ek' as input.¶

In Integrated Encryption mode, HPKE is employed to directly encrypt the plaintext, and the resulting ciphertext is included in the JWE ciphertext.¶

In Integrated Encryption mode:¶

The JWE Ciphertext MUST be the base64url encoded 'ct' value.¶
The JWE Initialization Vector value MUST be empty.¶
The JWE Authentication Tag MUST be empty.¶
The JWE Encrypted Key MUST be empty.¶
The "aad" parameter MUST take the Additional Authenticated Data encryption parameter defined in Step 14 of
Section 5.1 of [RFC7516] as input.¶

In this setup, the 'enc' (Encryption Algorithm) parameter MUST NOT be present because the ciphersuite (KEM, KDF, AEAD) is fully-specified in the 'alg' parameter itself.¶

This is a deviation from the rule in Section 4.1.2 of [RFC7516].¶

This example demonstrates the use of an encapsulated key with JSON Web Encryption Integrated Encryption and Compact Serialization:¶

eyJhbGciOiJIUEtFLUJhc2UtUDI1Ni1TSEEyNTYtQUVTMTI4R0NNIiwiZXBrIjp7Imt0eSI6IkVLIiwiZWsiOiJCQU9TeWV3M05JLUkwNEd2WU1MT3Y0cDBEVG5WMWZjWnBFVW10dGs0YkRTdDAtakxzY0FDN3h3MjdORTFHZ0VuMUgtM3ZXSFA5eW1BOHl4aFRmVDBkYjQifX0...afBw3T1hUNjci4qq3ZZ-9KxnttB0iCEO_GUqbIStqYqB5DgRDpyYSuvoH1mMA31qKPqB41ld5mSP34yUys6WJM7nstDJ1-4nqUdhRpgfkGTECA.

Figure 1: Integrated Encryption Encryption

4.4.2. Key Encryption

In Key Encryption mode, HPKE is used to encrypt the Content Encryption Key (CEK), and the resulting ciphertext is included in the JWE ciphertext. The (compressed) plaintext will be encrypted using the CEK as explained in Step 15 of Section 5.1 of [RFC7516].¶

In this mode, JWE JSON serialization MUST be used. The sender MUST place the 'epk' and 'alg' parameters in the per-recipient unprotected header to indicate the use of HPKE. Optionally, the per-recipient unprotected header MAY contain the 'kid' parameter used to identify the static recipient public key used by the sender. The 'enc' (Encryption Algorithm) parameter MUST be present to identify the content encryption algorithm used to perform encryption on the plaintext to produce the ciphertext. The "enc" Header Parameter MUST occur only within the JWE Protected Header.¶

In Key Encryption mode: - The JWE Encrypted Key MUST be the base64url encoded 'ct' value. - The JWE Initialization Vector MUST be produced as described in { Section 5.1 of RFC7516 } - The JWE Authentication Tag MUST be produced as described in { Section 5.1 of RFC7516 }¶

In JWE JSON Serialization, the following mechanisms MUST be selected to provide protection against an attacker who manipulates the encryption algorithm in the 'enc' parameter in the protected header. The attack is discussed in [I-D.draft-ietf-lamps-cms-cek-hkdf-sha256]:¶

The "aad" parameter MUST take the Additional Authenticated Data encryption parameter defined in Step 14 of Section 5.1 of [RFC7516] as input to encrypt the CEK. If the attacker changes encrytion algorithm in the 'enc' parameter prior to delivery to the recipient, then the recipient will derive a different authentication tag, leading to decryption failure and resulting in an OpenError.¶

This example demonstrates the use of an encapsulated key with a JSON Web Encryption with Key Encryption as described in this document.¶

{
  "protected": "eyJlbmMiOiJBMTI4R0NNIn0",
  "ciphertext": "S0qqrM3xXPUavbmL9LQkgUKRBu8BZ7DQWoT-mdNIZVU-ip_V-fbMokiGwp2aPM57DX3cXCK3TKHqdhZ8rSNduUja",
  "iv": "AzaXpooLg3ZxEASQ",
  "aad": "8J-SgCBhYWQ",
  "tag": "S0omWw35S0H7tyEHsmGLDw",
  "recipients": [
    {
      "encrypted_key": "yDVZLsO7-ecy_GCgEluwn9U723TCHNAzeYRRQPOfpHM",
      "header": {
        "kid": "urn:ietf:params:oauth:jwk-thumbprint:sha-256:adjwW6fyyZ94ZBjGjx_OpDEKHLGfd1ELkug_YmRAjCk",
        "alg": "HPKE-Base-P256-SHA256-AES128GCM",
        "epk": {
          "kty": "EK",
          "ek": "BHpP-u5JKziyUpqxNQqb0apHx1ecH2UzcRlhHR4ngJVS__gNu21DqqgPweuPpjglnXDnOuQ4kt9tHCs3PUzPxQs"
        }
      }
    },
    {
      "encrypted_key": "iS73TFqJ61gkmh4DHAXADx4wyftA7pnY",
      "header": {
        "kid": "urn:ietf:params:oauth:jwk-thumbprint:sha-256:D2FKlj9MTIQma5bwdOVXk5Zh3_d60knzlbmD-SyMNAI",
        "alg": "ECDH-ES+A128KW",
        "epk": {
          "kty": "EC",
          "crv": "P-256",
          "x": "nX6Y3DWC0olVe5H7-NkCzVDghsYSa_L9da3jzkHYkV8",
          "y": "wDshQdcaY0J08wx25V3ystQSNe_qjsCaaFeeRWJqcE0"
        }
      }
    }
  ]
}

Figure 2: Key Encryption Example

In the above example, the JWE Protected Header value is:¶

{
   "enc": "A128GCM"
}

4.5. Example Hybrid Key Agreement Computation

This example uses HPKE-Base-P256-SHA256-AES128GCM which corresponds to the following HPKE algorithm combination:¶

KEM: DHKEM(P-256, HKDF-SHA256)¶
KDF: HKDF-SHA256¶
AEAD: AES-128-GCM¶
Mode: Base¶
payload: "This is the content"¶
aad: ""¶

5. Ciphersuite Registration

This specification registers a number of ciphersuites for use with HPKE. A ciphersuite is thereby a combination of several algorithm configurations:¶

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, JOSE-HPKE cannot use an 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-<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.¶

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 JOSE makes the same assumptions. Hence, some form of public key distribution mechanism is assumed to exist but outside the scope of this document.¶

HPKE in Base mode does not offer authentication as part of the HPKE KEM. In this case JOSE constructs like JWS and JSON Web Tokens (JWTs) can be used to add authentication. HPKE also offers modes that offer authentication.¶

HPKE relies on a source of randomness to be available on the device. In Key Agreement with Key Wrapping mode, CEK has to be randomly generated and it MUST be ensured that the guidelines in [RFC8937] for random number generations are followed.¶

7. IANA Considerations

The following is added to the "JSON Web Key Types" registry:¶

"kty" Parameter Value: "EK"¶
Key Type Description: HPKE¶
JOSE Implementation Requirements: Optional¶
Change Controller: IESG¶
Specification Document(s): [[TBD: This RFC]]¶

The following is added to the "JSON Web Key Parameters" registry:¶

Parameter Name: "ek"¶
Parameter Description: Encapsulated Key¶
Parameter Information Class: Public¶
Used with "kty" Value(s): "EK"¶
Specification Document(s): [[TBD: This RFC]]¶

This document requests IANA to add new values to the 'JOSE Algorithms' and to the 'JOSE Header Parameters' registries in the 'Standards Action With Expert Review category'.¶

7.1. JOSE Algorithms Registry (Direct Key Agreement)

Algorithm Name: HPKE-Base-P256-SHA256-AES128GCM¶
Algorithm Description: Cipher suite for JOSE-HPKE in Base Mode that uses the DHKEM(P-256, HKDF-SHA256) KEM, the HKDF-SHA256 KDF and the AES-128-GCM AEAD.¶
Algorithm Usage Location(s): "alg"¶
JOSE Implementation Requirements: Optional¶
Change Controller: IESG¶
Specification Document(s): [[TBD: This RFC]]¶
Algorithm Analysis Documents(s): TODO¶
Algorithm Name: HPKE-Base-P384-SHA384-AES256GCM¶
Algorithm Description: Cipher suite for JOSE-HPKE in Base Mode that uses the DHKEM(P-384, HKDF-SHA384) KEM, the HKDF-SHA384 KDF, and the AES-256-GCM AEAD.¶
Algorithm Usage Location(s): "alg"¶
JOSE Implementation Requirements: Optional¶
Change Controller: IESG¶
Specification Document(s): [[TBD: This RFC]]¶
Algorithm Analysis Documents(s): TODO¶
Algorithm Name: HPKE-Base-P521-SHA512-AES256GCM¶
Algorithm Description: Cipher suite for JOSE-HPKE in Base Mode that uses the DHKEM(P-521, HKDF-SHA512) KEM, the HKDF-SHA512 KDF, and the AES-256-GCM AEAD.¶
Algorithm Usage Location(s): "alg"¶
JOSE Implementation Requirements: Optional¶
Change Controller: IESG¶
Specification Document(s): [[TBD: This RFC]]¶
Algorithm Analysis Documents(s): TODO¶
Algorithm Name: HPKE-Base-X25519-SHA256-AES128GCM¶
Algorithm Description: Cipher suite for JOSE-HPKE in Base Mode that uses the DHKEM(X25519, HKDF-SHA256) KEM, the HKDF-SHA256 KDF, and the AES-128-GCM AEAD.¶
Algorithm Usage Location(s): "alg"¶
JOSE Implementation Requirements: Optional¶
Change Controller: IESG¶
Specification Document(s): [[TBD: This RFC]]¶
Algorithm Analysis Documents(s): TODO¶
Algorithm Name: HPKE-Base-X25519-SHA256-ChaCha20Poly1305¶
Algorithm Description: Cipher suite for JOSE-HPKE in Base Mode that uses the DHKEM(X25519, HKDF-SHA256) KEM, the HKDF-SHA256 KDF, and the ChaCha20Poly1305 AEAD.¶
Algorithm Usage Location(s): "alg"¶
JOSE Implementation Requirements: Optional¶
Change Controller: IESG¶
Specification Document(s): [[TBD: This RFC]]¶
Algorithm Analysis Documents(s): TODO¶
Algorithm Name: HPKE-Base-X448-SHA512-AES256GCM¶
Algorithm Description: Cipher suite for JOSE-HPKE in Base Mode that uses the DHKEM(X448, HKDF-SHA512) KEM, the HKDF-SHA512 KDF, and the AES-256-GCM AEAD.¶
Algorithm Usage Location(s): "alg"¶
JOSE Implementation Requirements: Optional¶
Change Controller: IESG¶
Specification Document(s): [[TBD: This RFC]]¶
Algorithm Analysis Documents(s): TODO¶
Algorithm Name: HPKE-Base-X448-SHA512-ChaCha20Poly1305¶
Algorithm Description: Cipher suite for JOSE-HPKE in Base Mode that uses the DHKEM(X448, HKDF-SHA512) KEM, the HKDF-SHA512 KDF, and the ChaCha20Poly1305 AEAD.¶
Algorithm Usage Location(s): "alg"¶
JOSE Implementation Requirements: Optional¶
Change Controller: IESG¶
Specification Document(s): [[TBD: This RFC]]¶
Algorithm Analysis Documents(s): TODO¶

7.2. JOSE Algorithms Registry (Key Agreement with Key Wrapping)

Algorithm Name: HPKE-Base-P256-SHA256-AES128GCMKW¶
Algorithm Description: Cipher suite for JOSE-HPKE in Base Mode that uses the DHKEM(P-256, HKDF-SHA256) KEM, the HKDF-SHA256 KDF and Key wrapping with the AES-128-GCM AEAD.¶
Algorithm Usage Location(s): "alg"¶
JOSE Implementation Requirements: Optional¶
Change Controller: IESG¶
Specification Document(s): [[TBD: This RFC]]¶
Algorithm Analysis Documents(s): TODO¶
Algorithm Name: HPKE-Base-P384-SHA384-AES256GCMKW¶
Algorithm Description: Cipher suite for JOSE-HPKE in Base Mode that uses the DHKEM(P-384, HKDF-SHA384) KEM, the HKDF-SHA384 KDF, and Key wrapping with the AES-256-GCM AEAD.¶
Algorithm Usage Location(s): "alg"¶
JOSE Implementation Requirements: Optional¶
Change Controller: IESG¶
Specification Document(s): [[TBD: This RFC]]¶
Algorithm Analysis Documents(s): TODO¶
Algorithm Name: HPKE-Base-P521-SHA512-AES256GCMKW¶
Algorithm Description: Cipher suite for JOSE-HPKE in Base Mode that uses the DHKEM(P-521, HKDF-SHA512) KEM, the HKDF-SHA512 KDF, and Key wrapping with the AES-256-GCM AEAD.¶
Algorithm Usage Location(s): "alg"¶
JOSE Implementation Requirements: Optional¶
Change Controller: IESG¶
Specification Document(s): [[TBD: This RFC]]¶
Algorithm Analysis Documents(s): TODO¶
Algorithm Name: HPKE-Base-X25519-SHA256-AES128GCMKW¶
Algorithm Description: Cipher suite for JOSE-HPKE in Base Mode that uses the DHKEM(X25519, HKDF-SHA256) KEM, the HKDF-SHA256 KDF, and Key wrapping with the AES-128-GCM AEAD.¶
Algorithm Usage Location(s): "alg"¶
JOSE Implementation Requirements: Optional¶
Change Controller: IESG¶
Specification Document(s): [[TBD: This RFC]]¶
Algorithm Analysis Documents(s): TODO¶
Algorithm Name: HPKE-Base-X25519-SHA256-ChaCha20Poly1305KW¶
Algorithm Description: Cipher suite for JOSE-HPKE in Base Mode that uses the DHKEM(X25519, HKDF-SHA256) KEM, the HKDF-SHA256 KDF, and Key wrapping with the ChaCha20Poly1305 AEAD.¶
Algorithm Usage Location(s): "alg"¶
JOSE Implementation Requirements: Optional¶
Change Controller: IESG¶
Specification Document(s): [[TBD: This RFC]]¶
Algorithm Analysis Documents(s): TODO¶
Algorithm Name: HPKE-Base-X448-SHA512-AES256GCMKW¶
Algorithm Description: Cipher suite for JOSE-HPKE in Base Mode that uses the DHKEM(X448, HKDF-SHA512) KEM, the HKDF-SHA512 KDF, and Key wrapping with the AES-256-GCM AEAD.¶
Algorithm Usage Location(s): "alg"¶
JOSE Implementation Requirements: Optional¶
Change Controller: IESG¶
Specification Document(s): [[TBD: This RFC]]¶
Algorithm Analysis Documents(s): TODO¶
Algorithm Name: HPKE-Base-X448-SHA512-ChaCha20Poly1305KW¶
Algorithm Description: Cipher suite for JOSE-HPKE in Base Mode that uses the DHKEM(X448, HKDF-SHA512) KEM, the HKDF-SHA512 KDF, and Key wrapping with the ChaCha20Poly1305 AEAD.¶
Algorithm Usage Location(s): "alg"¶
JOSE Implementation Requirements: Optional¶
Change Controller: IESG¶
Specification Document(s): [[TBD: This RFC]]¶
Algorithm Analysis Documents(s): TODO¶

7.3. JOSE Header Parameters

7.3.1. Authentication Using a Pre-Shared Key

Parameter Name: "psk_id"¶
Parameter Description: A key identifier (kid) for the pre-shared key as defined in { Section 5.1.1 of RFC9180 }¶
Parameter Information Class: Public¶
Change Controller: IESG¶
Specification Document(s): [[This specification]]¶

7.3.2. Authentication Using an Asymmetric Key

Parameter Name: "auth_kid"¶
Parameter Description: A key identifier (kid) for the asymmetric key as defined in { Section 5.1.4 of RFC9180 }¶
Parameter Information Class: Public¶
Change Controller: IESG¶
Specification Document(s): [[This specification]]¶

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>.
[RFC7516]: Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)", RFC 7516, DOI 10.17487/RFC7516, May 2015, <https://www.rfc-editor.org/rfc/rfc7516>.
[RFC7517]: Jones, M., "JSON Web Key (JWK)", RFC 7517, DOI 10.17487/RFC7517, May 2015, <https://www.rfc-editor.org/rfc/rfc7517>.
[RFC7518]: Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, DOI 10.17487/RFC7518, May 2015, <https://www.rfc-editor.org/rfc/rfc7518>.
[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>.
[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>.
[I-D.draft-ietf-lamps-cms-cek-hkdf-sha256]: Housley, R., "Encryption Key Derivation in the Cryptographic Message Syntax (CMS) using HKDF with SHA-256", Work in Progress, Internet-Draft, draft-ietf-lamps-cms-cek-hkdf-sha256-00, 29 January 2024, <https://datatracker.ietf.org/doc/html/draft-ietf-lamps-cms-cek-hkdf-sha256-00>.
[I-D.ietf-cose-hpke]: Tschofenig, H., Steele, O., Daisuke, A., and L. Lundblade, "Use of Hybrid Public-Key Encryption (HPKE) with CBOR Object Signing and Encryption (COSE)", Work in Progress, Internet-Draft, draft-ietf-cose-hpke-07, 22 October 2023, <https://datatracker.ietf.org/doc/html/draft-ietf-cose-hpke-07>.
[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>.

Acknowledgments

This specification leverages text from [I-D.ietf-cose-hpke]. We would like to thank Matt Chanda, Ilari Liusvaara and Aaron Parecki for their feedback.¶

Authors' Addresses

Tirumaleswar Reddy

Nokia

Bangalore

Karnataka

India

Email: kondtir@gmail.com

Hannes Tschofenig

Austria

Email: hannes.tschofenig@gmx.net

Aritra Banerjee

Nokia

Munich

Germany

Email: aritra.banerjee@nokia.com

Orie Steele

Transmute

United States

Email: orie@transmute.industries

Michael B. Jones

independent