RFC 8037

CFRG Elliptic Curve Diffie-Hellman (ECDH) and Signatures in JSON Object Signing and Encryption (JOSE)

📅 published January 2017, from ietf

RFC 8037 📜💖 CFRG Elliptic Curve Diffie-Hellman (ECDH) and Signatures in JSON Object Signing and Encryption (JOSE)

Okay bestie, let's get into it! ✨ This RFC is by I. Liusvaara, who wrote it as an Independent author 🦋. It's on the Standards Track 👑, dated January 2017 🌸, with ISSN 2070-1721. It doesn't obsolete or update anything, so it's a fresh start 🧚.

Abstract ✨

So the whole point is this 💅. It defines how to use the Diffie-Hellman algorithms "X25519" and "X448", plus the signature algorithms "Ed25519" and "Ed448", all from the IRTF CFRG elliptic curves work 🌈. And it does it inside JOSE (JSON Object Signing and Encryption) 🎀.

Status of This Memo 🌸

This is an Internet Standards Track document 👑.

It's a product of the Internet Engineering Task Force (IETF) 💜. It represents the consensus of the IETF community, got public review, and was approved by the Internet Engineering Steering Group (IESG) 🫶. If you want more on Internet Standards, check Section 2 of RFC 7841 🍓.

Info about the current status, errata, and how to send feedback lives at http://www.rfc-editor.org/info/rfc8037 🔥.

Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved 🌈.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication 📜. Please read these carefully, because they describe your rights and restrictions 🙈. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions, and they come without warranty as described in the Simplified BSD License 💅.

Table of Contents 🧚

1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
  1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
2.  Key Type "OKP"  . . . . . . . . . . . . . . . . . . . . . . .   3
3.  Algorithms  . . . . . . . . . . . . . . . . . . . . . . . . .   4
  3.1.  Signatures  . . . . . . . . . . . . . . . . . . . . . . .   4
    3.1.1.  Signing . . . . . . . . . . . . . . . . . . . . . . .   4
    3.1.2.  Verification  . . . . . . . . . . . . . . . . . . . .   4
  3.2.  ECDH-ES . . . . . . . . . . . . . . . . . . . . . . . . .   4
    3.2.1.  Performing the ECDH Operation . . . . . . . . . . . .   5
4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
  6.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
  6.2.  Informative References  . . . . . . . . . . . . . . . . .   8
Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .   9
  A.1.  Ed25519 Private Key . . . . . . . . . . . . . . . . . . .   9
  A.2.  Ed25519 Public Key  . . . . . . . . . . . . . . . . . . .   9
  A.3.  JWK Thumbprint Canonicalization . . . . . . . . . . . . .   9
  A.4.  Ed25519 Signing . . . . . . . . . . . . . . . . . . . . .  10
  A.5.  Ed25519 Validation  . . . . . . . . . . . . . . . . . . .  11
  A.6.  ECDH-ES with X25519 . . . . . . . . . . . . . . . . . . .  11
  A.7.  ECDH-ES with X448 . . . . . . . . . . . . . . . . . . . .  12
Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  14
Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  14

1. Introduction 🦋

Okay so the Internet Research Task Force (IRTF) Crypto Forum Research Group (CFRG) picked some new stuff 💖. For Diffie-Hellman they chose "X25519" and "X448" ([RFC7748]), and for signatures "Ed25519" and "Ed448" ([RFC8032]), all for asymmetric key crypto 🔥. This doc explains how to use those in JOSE so everything works together interoperably ✨.

This document sets the conventions for use with [RFC7515], [RFC7516], and [RFC7517] 🎀.

The CFRG also defined two pairs of isogenous elliptic curves underneath these algorithms 🧚. But those curves aren't directly exposed, because the algorithms on top are good enough for JOSE and way easier to use 💅.

All inputs to and outputs from the Elliptic Curve Diffie-Hellman (ECDH) and signature functions are defined to be octet strings 🌈, except for the outputs of verification functions, which are booleans 🙈.

1.1. Terminology 💜

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] 📜.

"JWS Signing Input" and "JWS Signature" are defined by [RFC7515] 🫶.

"Key Agreement with Elliptic Curve Diffie-Hellman Ephemeral Static" is defined by Section 4.6 of [RFC7518] 🍓.

The JOSE key format ("JSON Web Key (JWK)") is defined by [RFC7517], and thumbprints for it ("JSON Web Key (JWK) Thumbprint") are in [RFC7638] 🔥.

2. Key Type "OKP" 🌸

A brand new key type (kty) value, "OKP" (Octet Key Pair), is defined for public key algorithms that use octet strings as private and public keys 💖. It has these parameters:

  • The parameter "kty" MUST be "OKP".
  • The parameter "crv" MUST be present and contain the subtype of the key (from the "JSON Web Elliptic Curve" registry) 👑.
  • The parameter "x" MUST be present and contain the public key encoded using the base64url [RFC4648] encoding 🧚.
  • The parameter "d" MUST be present for private keys and contain the private key encoded using the base64url encoding. This parameter MUST NOT be present for public keys 🙈.
Note: Do not assume there's an underlying elliptic curve, even though the "crv" and "x" parameters exist 💀. (For instance, this key type could be extended to represent Diffie-Hellman (DH) algorithms based on hyperelliptic surfaces 🌈.)

When calculating JWK Thumbprints [RFC7638], the three public key fields go into the hash input in lexicographic order: "crv", "kty", and "x" 🎀.

3. Algorithms 🦋

3.1. Signatures 💅

For signing data with the Edwards-curve Digital Signature Algorithm (EdDSA) using "JSON Web Signature (JWS)" [RFC7515], the algorithm "EdDSA" is defined here, to be applied as the value of the "alg" parameter ✨.

These key subtypes are defined for use with EdDSA:

"crv"             EdDSA Variant
Ed25519           Ed25519
Ed448             Ed448

The key type used with these keys is "OKP", and the signing algorithm is "EdDSA" 🔥. These subtypes MUST NOT be used for Elliptic Curve Diffie-Hellman Ephemeral Static (ECDH-ES) 🙈.

The EdDSA variant depends on the key's subtype (Ed25519 for "Ed25519" and Ed448 for "Ed448") 💖.

3.1.1. Signing 🌸

Signing is done by applying the signing algorithm from [RFC8032] to the private key (as private key), the public key (as public key), and the JWS Signing Input (as message) 🧚. The result is the JWS Signature 🫶. All inputs and outputs are octet strings 💜.

3.1.2. Verification 🌈

Verification is done by applying the verification algorithm from [RFC8032] to the public key (as public key), the JWS Signing Input (as message), and the JWS Signature (as signature) ✨. All inputs are octet strings 🎀. If the algorithm accepts, the signature is valid; otherwise, it's invalid 👑.

3.2. ECDH-ES 🌸

These key subtypes are defined for "Key Agreement with Elliptic Curve Diffie-Hellman Ephemeral Static" (ECDH-ES) 💖:

"crv"             ECDH Function Applied
X25519            X25519
X448              X448

The key type used with these keys is "OKP". These subtypes MUST NOT be used for signing 🙈.

Section 4.6 of [RFC7518] defines the ECDH-ES algorithms "ECDH-ES+A128KW", "ECDH-ES+A192KW", "ECDH-ES+A256KW", and "ECDH-ES" 🔥.

3.2.1. Performing the ECDH Operation 🧚

The "x" parameter of the "epk" field is set like this 💅:

Apply the appropriate ECDH function to the ephemeral private key (as scalar input) and the standard base point (as u-coordinate input) ✨. The base64url encoding of the output is the value for the "x" parameter of the "epk" field 🦋. All inputs and outputs are octet strings 🌈.

The Z value (raw key agreement output) for key agreement, used in the subsequent Key Derivation Function (KDF) per Section 4.6.2 of [RFC7518], is determined like this 👑:

Apply the appropriate ECDH function to the ephemeral private key (as scalar input) and receiver public key (as u-coordinate input) 💖. The output is the Z value 🫶. All inputs and outputs are octet strings 💜.

4. Security Considerations 💀

Security considerations from [RFC7748] and [RFC8032] apply here 🔥.

Okay, this section is SERIOUS, bestie 😭.

Do not separate key material from information about what key subtype it's for 🙈. When you use keys, check that the algorithm is compatible with the key's subtype 🚨. Doing otherwise opens the system up to attacks through mixing up algorithms 💀. Mixing up signature and Message Authentication Code (MAC) algorithms is especially dangerous 😱.

Even though for Ed25519 and Ed448 the signature binds the key used for signing, do not assume this 🙅, because lots of signature algorithms fail to make that binding 💅. If you want key-binding, include the key used for signing either inside the JWS protected header or the data being signed 🎀.

If key generation or batch signature verification is performed, a well-seeded cryptographic random number generator is REQUIRED 🎲. Signing and non-batch signature verification are deterministic operations and don't need random numbers of any kind ✨.

The JSON Web Algorithm (JWA) ECDH-ES KDF construction does not mix keys into the final shared secret 😬. In key exchange, that mixing could be a seriously bad mistake 💀; but here, either the receiver public key has to be chosen maliciously or the sender has to be malicious in order to cause problems 😈. In either case, all security evaporates 🫠.

The nominal security strengths of X25519 and X448 are ~126 and ~223 bits 📊. Therefore, using 256-bit symmetric encryption (especially key wrapping and encryption) with X448 is RECOMMENDED 💖.

That's the first part, bestie! More is coming 🫶✨

5. IANA Considerations ✨

okay bestie, this part is all about registries 📋💅 IANA keeps the official lists, and this section says exactly which new entries get added to them. Let's go!

The following has been added to the "JSON Web Key Types" registry:

  • "kty" Parameter Value: "OKP"
  • Key Type Description: Octet string key pairs
  • JOSE Implementation Requirements: Optional
  • Change Controller: IESG
  • Specification Document(s): Section 2 of RFC 8037

OKP is the new key type, and it's giving main character energy 👑🌸

The following has been added to the "JSON Web Key Parameters" registry:

  • Parameter Name: "crv"
  • Parameter Description: The subtype of key pair
  • Parameter Information Class: Public
  • Used with "kty" Value(s): "OKP"
  • Change Controller: IESG
  • Specification Document(s): Section 2 of RFC 8037
  • Parameter Name: "d"
  • Parameter Description: The private key
  • Parameter Information Class: Private
  • Used with "kty" Value(s): "OKP"
  • Change Controller: IESG
  • Specification Document(s): Section 2 of RFC 8037
  • Parameter Name: "x"
  • Parameter Description: The public key
  • Parameter Information Class: Public
  • Used with "kty" Value(s): "OKP"
  • Change Controller: IESG
  • Specification Document(s): Section 2 of RFC 8037

The following has been added to the "JSON Web Signature and Encryption Algorithms" registry:

  • Algorithm Name: "EdDSA"
  • Algorithm Description: EdDSA signature algorithms
  • Algorithm Usage Location(s): "alg"
  • JOSE Implementation Requirements: Optional
  • Change Controller: IESG
  • Specification Document(s): Section 3.1 of RFC 8037
  • Algorithm Analysis Documents(s): [RFC8032]

The following has been added to the "JSON Web Key Elliptic Curve" registry:

  • Curve Name: "Ed25519"
  • Curve Description: Ed25519 signature algorithm key pairs
  • JOSE Implementation Requirements: Optional
  • Change Controller: IESG
  • Specification Document(s): Section 3.1 of RFC 8037
  • Curve Name: "Ed448"
  • Curve Description: Ed448 signature algorithm key pairs
  • JOSE Implementation Requirements: Optional
  • Change Controller: IESG
  • Specification Document(s): Section 3.1 of RFC 8037
  • Curve name: "X25519"
  • Curve Description: X25519 function key pairs
  • JOSE Implementation Requirements: Optional
  • Change Controller: IESG
  • Specification Document(s): Section 3.2 of RFC 8037
  • Analysis Documents(s): [RFC7748]
  • Curve Name: "X448"
  • Curve Description: X448 function key pairs
  • JOSE Implementation Requirements: Optional
  • Change Controller: IESG
  • Specification Document(s): Section 3.2 of RFC 8037
  • Analysis Documents(s): [RFC7748]

6. References 📚

6.1. 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,
           <http://www.rfc-editor.org/info/rfc2119>.

[RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
           Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
           <http://www.rfc-editor.org/info/rfc4648>.

[RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
           Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
           2015, <http://www.rfc-editor.org/info/rfc7515>.

[RFC7517]  Jones, M., "JSON Web Key (JWK)", RFC 7517,
           DOI 10.17487/RFC7517, May 2015,
           <http://www.rfc-editor.org/info/rfc7517>.

[RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
           DOI 10.17487/RFC7518, May 2015,
           <http://www.rfc-editor.org/info/rfc7518>.

[RFC7638]  Jones, M. and N. Sakimura, "JSON Web Key (JWK)
           Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September
           2015, <http://www.rfc-editor.org/info/rfc7638>.

[RFC7748]  Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
           for Security", RFC 7748, DOI 10.17487/RFC7748, January
           2016, <http://www.rfc-editor.org/info/rfc7748>.

[RFC8032]  Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
           Signature Algorithm (EdDSA)", RFC 8032,
           DOI 10.17487/RFC8032, January 2017,
           <http://www.rfc-editor.org/info/rfc8032>.

6.2. Informative References

[RFC7516]  Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
           RFC 7516, DOI 10.17487/RFC7516, May 2015,
           <http://www.rfc-editor.org/info/rfc7516>.

Appendix A. Examples 🧁

To the extent possible, these examples use material taken from test vectors of [RFC7748] and [RFC8032]. 🧪

A.1. Ed25519 Private Key

{"kty":"OKP","crv":"Ed25519",
"d":"nWGxne_9WmC6hEr0kuwsxERJxWl7MmkZcDusAxyuf2A",
"x":"11qYAYKxCrfVS_7TyWQHOg7hcvPapiMlrwIaaPcHURo"}

The hexadecimal dump of private key is:

9d 61 b1 9d ef fd 5a 60 ba 84 4a f4 92 ec 2c c4
44 49 c5 69 7b 32 69 19 70 3b ac 03 1c ae 7f 60

And of the public key is:

d7 5a 98 01 82 b1 0a b7 d5 4b fe d3 c9 64 07 3a
0e e1 72 f3 da a6 23 25 af 02 1a 68 f7 07 51 1a

A.2. Ed25519 Public Key

This is the public part of the previous private key (which just omits "d"):

{"kty":"OKP","crv":"Ed25519",
"x":"11qYAYKxCrfVS_7TyWQHOg7hcvPapiMlrwIaaPcHURo"}

A.3. JWK Thumbprint Canonicalization

The JWK Thumbprint canonicalization of the two examples above (with a linebreak inserted for formatting reasons) is:

{"crv":"Ed25519","kty":"OKP","x":"11qYAYKxCrfVS_7TyWQHOg7hcvPapiMlrwI
aaPcHURo"}

Which has the SHA-256 hash (in hexadecimal) of 90facafea9b1556698540f70c0117a22ea37bd5cf3ed3c47093c1707282b4b89, which results in the base64url encoded JWK Thumbprint representation of "kPrK_qmxVWaYVA9wwBF6Iuo3vVzz7TxHCTwXBygrS4k".

A.4. Ed25519 Signing

The JWS protected header is:

{"alg":"EdDSA"}

This has the base64url encoding of:

eyJhbGciOiJFZERTQSJ9

The payload is (text):

Example of Ed25519 signing

This has the base64url encoding of:

RXhhbXBsZSBvZiBFZDI1NTE5IHNpZ25pbmc

The JWS signing input is (a concatenation of base64url encoding of the (protected) header, a dot, and base64url encoding of the payload) is:

eyJhbGciOiJFZERTQSJ9.RXhhbXBsZSBvZiBFZDI1NTE5IHNpZ25pbmc

Applying the Ed25519 signing algorithm using the private key, public key, and the JWS signing input yields the signature (hex):

86 0c 98 d2 29 7f 30 60 a3 3f 42 73 96 72 d6 1b
53 cf 3a de fe d3 d3 c6 72 f3 20 dc 02 1b 41 1e
9d 59 b8 62 8d c3 51 e2 48 b8 8b 29 46 8e 0e 41
85 5b 0f b7 d8 3b b1 5b e9 02 bf cc b8 cd 0a 02

Converting this to base64url yields:

hgyY0il_MGCjP0JzlnLWG1PPOt7-09PGcvMg3AIbQR6dWbhijcNR4ki4iylGjg5BhVsPt
9g7sVvpAr_MuM0KAg

So the compact serialization of the JWS is (a concatenation of signing input, a dot, and base64url encoding of the signature):

eyJhbGciOiJFZERTQSJ9.RXhhbXBsZSBvZiBFZDI1NTE5IHNpZ25pbmc.hgyY0il_MGCj
P0JzlnLWG1PPOt7-09PGcvMg3AIbQR6dWbhijcNR4ki4iylGjg5BhVsPt9g7sVvpAr_Mu
M0KAg

A.5. Ed25519 Validation

The JWS from the example above is:

eyJhbGciOiJFZERTQSJ9.RXhhbXBsZSBvZiBFZDI1NTE5IHNpZ25pbmc.hgyY0il_MGCj
P0JzlnLWG1PPOt7-09PGcvMg3AIbQR6dWbhijcNR4ki4iylGjg5BhVsPt9g7sVvpAr_Mu
M0KAg

This has 2 dots in it, so it might be valid a JWS. Base64url decoding the protected header yields:

{"alg":"EdDSA"}

So this is an EdDSA signature. Now the key has: "kty":"OKP" and "crv":"Ed25519", so the signature is Ed25519 signature.

The signing input is the part before the second dot:

eyJhbGciOiJFZERTQSJ9.RXhhbXBsZSBvZiBFZDI1NTE5IHNpZ25pbmc

Applying the Ed25519 verification algorithm to the public key, JWS signing input, and the signature yields true. So the signature is valid. The message is the base64url decoding of the part between the dots:

Example of Ed25519 Signing

A.6. ECDH-ES with X25519

The public key to encrypt to is:

{"kty":"OKP","crv":"X25519","kid":"Bob",
"x":"3p7bfXt9wbTTW2HC7OQ1Nz-DQ8hbeGdNrfx-FG-IK08"}

The public key from the target key is (hex):

de 9e db 7d 7b 7d c1 b4 d3 5b 61 c2 ec e4 35 37
3f 83 43 c8 5b 78 67 4d ad fc 7e 14 6f 88 2b 4f

The ephemeral secret happens to be (hex):

77 07 6d 0a 73 18 a5 7d 3c 16 c1 72 51 b2 66 45
df 4c 2f 87 eb c0 99 2a b1 77 fb a5 1d b9 2c 2a

So the ephemeral public key is X25519(ephkey, G) (hex):

85 20 f0 09 89 30 a7 54 74 8b 7d dc b4 3e f7 5a
0d bf 3a 0d 26 38 1a f4 eb a4 a9 8e aa 9b 4e 6a

This is represented as the ephemeral public key value:

{"kty":"OKP","crv":"X25519",
"x":"hSDwCYkwp1R0i33ctD73Wg2_Og0mOBr066SpjqqbTmo"}

So the protected header could be, for example:

{"alg":"ECDH-ES+A128KW","epk":{"kty":"OKP","crv":"X25519",
"x":"hSDwCYkwp1R0i33ctD73Wg2_Og0mOBr066SpjqqbTmo"},
"enc":"A128GCM","kid":"Bob"}

And the sender computes the DH Z value as X25519(ephkey, recv_pub) (hex):

4a 5d 9d 5b a4 ce 2d e1 72 8e 3b f4 80 35 0f 25
e0 7e 21 c9 47 d1 9e 33 76 f0 9b 3c 1e 16 17 42

The receiver computes the DH Z value as X25519(seckey, ephkey_pub) (hex):

4a 5d 9d 5b a4 ce 2d e1 72 8e 3b f4 80 35 0f 25
e0 7e 21 c9 47 d1 9e 33 76 f0 9b 3c 1e 16 17 42

This is the same as the sender's value (both sides run this through the KDF before using it as a direct encryption key or AES128-KW key).

A.7. ECDH-ES with X448

The public key to encrypt to (with a linebreak inserted for formatting reasons) is:

{"kty":"OKP","crv":"X448","kid":"Dave",
"x":"PreoKbDNIPW8_AtZm2_sz22kYnEHvbDU80W0MCfYuXL8PjT7QjKhPKcG3LV67D2
uB73BxnvzNgk"}

The public key from the target key is (hex):

3e b7 a8 29 b0 cd 20 f5 bc fc 0b 59 9b 6f ec cf
6d a4 62 71 07 bd b0 d4 f3 45 b4 30 27 d8 b9 72
fc 3e 34 fb 42 32 a1 3c a7 06 dc b5 7a ec 3d ae
07 bd c1 c6 7b f3 36 09

The ephemeral secret happens to be (hex):

9a 8f 49 25 d1 51 9f 57 75 cf 46 b0 4b 58 00 d4
ee 9e e8 ba e8 bc 55 65 d4 98 c2 8d d9 c9 ba f5
74 a9 41 97 44 89 73 91 00 63 82 a6 f1 27 ab 1d
9a c2 d8 c0 a5 98 72 6b

So the ephemeral public key is X448(ephkey, G) (hex):

9b 08 f7 cc 31 b7 e3 e6 7d 22 d5 ae a1 21 07 4a
27 3b d2 b8 3d e0 9c 63 fa a7 3d 2c 22 c5 d9 bb
c8 36 64 72 41 d9 53 d4 0c 5b 12 da 88 12 0d 53
17 7f 80 e5 32 c4 1f a0

This is packed into the ephemeral public key value (a linebreak inserted for formatting purposes):

{"kty":"OKP","crv":"X448",
"x":"mwj3zDG34-Z9ItWuoSEHSic70rg94Jxj-qc9LCLF2bvINmRyQdlT1AxbEtqIEg1
TF3-A5TLEH6A"}

So the protected header could be, for example (a linebreak inserted for formatting purposes):

{"alg":"ECDH-ES+A256KW","epk":{"kty":"OKP","crv":"X448",
"x":"mwj3zDG34-Z9ItWuoSEHSic70rg94Jxj-qc9LCLF2bvINmRyQdlT1AxbEtqIEg1
TF3-A5TLEH6A"},"enc":"A256GCM","kid":"Dave"}

And the sender computes the DH Z value as X448(ephkey,recv_pub) (hex):

07 ff f4 18 1a c6 cc 95 ec 1c 16 a9 4a 0f 74 d1
2d a2 32 ce 40 a7 75 52 28 1d 28 2b b6 0c 0b 56
fd 24 64 c3 35 54 39 36 52 1c 24 40 30 85 d5 9a
44 9a 50 37 51 4a 87 9d

The receiver computes the DH Z value as X448(seckey, ephkey_pub) (hex):

07 ff f4 18 1a c6 cc 95 ec 1c 16 a9 4a 0f 74 d1
2d a2 32 ce 40 a7 75 52 28 1d 28 2b b6 0c 0b 56
fd 24 64 c3 35 54 39 36 52 1c 24 40 30 85 d5 9a
44 9a 50 37 51 4a 87 9d

This is the same as the sender's value (both sides run this through KDF before using it as the direct encryption key or AES256-KW key).

Acknowledgements 💖

Thanks to Michael B. Jones for his comments on an initial draft of this document and editorial help.

Thanks to Matt Miller for some editorial help.

Author's Address 🦋

Ilari Liusvaara Independent

Email: ilariliusvaara@welho.com

📦 where this page comes from