Internet DRAFT - draft-amringer-jose-chacha
draft-amringer-jose-chacha
(No Working Group) G. Amringer
Internet-Draft January 9, 2020
Intended status: Informational
Expires: July 12, 2020
Chacha derived AEAD algorithms in JSON Object Signing and Encryption
(JOSE)
draft-amringer-jose-chacha-02
Abstract
This document defines how to use the AEAD algorithms
"AEAD_XCHACHA20_POLY1305" and "AEAD_CHACHA20_POLY1305" from [RFC8439]
and [I-D.irtf-cfrg-xchacha] in JSON Object Signing and Encryption
(JOSE).
Status of This Memo
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This Internet-Draft will expire on July 12, 2020.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notation and Conventions . . . . . . . . . . . . . . . . 2
2. Key Encryption . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Algorithms . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Header Parameters Used for Key Encryption . . . . . . . . 3
2.2.1. "iv" (Initialization Vector) Header Parameter . . . . 3
2.2.2. "tag" (Authentication Tag) Header Parameter . . . . . 4
3. Key Agreement with Elliptic Curve Diffie-Hellman Ephemeral
Static . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Content Encryption . . . . . . . . . . . . . . . . . . . . . 4
4.1. Algorithms . . . . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 6
6.2. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Appendix A. Example using XC20PKW . . . . . . . . . . . . . . . 7
Appendix B. Example using ECDH-ES+XC20PKW . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
The Internet Research Task Force (IRTF) Crypto Forum Research Group
(CFRG) defined the ChaCha20 and Poly1305 algorithms to be used in
IETF protocols both independantly and as an AEAD construction
([RFC8439]). It has also been presented with a definition of an
eXtended-nonce variant ([I-D.irtf-cfrg-xchacha]) for use in stateless
contexts. This document defines how to use those algorithms in JOSE
in an interoperable manner.
This document defines the conventions to use in the context of
[RFC7516], and [RFC7517].
1.1. Notation and Conventions
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].
The JOSE key format ("JSON Web Key (JWK)") is defined by [RFC7517]
and thumbprints for it ("JSON Web Key (JWK) Thumbprint") in
[RFC7638].
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2. Key Encryption
2.1. Algorithms
This section defines the specifics of encrypting a JWE Content
Encryption Key (CEK) with AEAD_CHACHA20_POLY1305 [RFC8439] and
AEAD_XCHACHA20_POLY1305 [I-D.irtf-cfrg-xchacha].
Use of an Initialization Vector (IV) is REQUIRED with this algorithm.
The IV is represented in base64url-encoded form as the "iv"
(initialization vector) Header Parameter value.
The Additional Authenticated Data value used is the empty octet
string.
The JWE Encrypted Key value is the ciphertext output.
The Authentication Tag output is represented in base64url-encoded
form as the "tag" (authentication tag) Header Parameter value.
The following "alg" (algorithm) Header Parameter values are used to
indicate that the JWE Encrypted Key is the result of encrypting the
CEK using the corresponding algorithm and IV size:
+-------------------------+----------+-------------+
| Algorithm | IV size | "alg" value |
+-------------------------+----------+-------------+
| AEAD_CHACHA20_POLY1305 | 96 bits | C20PKW |
| AEAD_XCHACHA20_POLY1305 | 192 bits | XC20PKW |
+-------------------------+----------+-------------+
2.2. Header Parameters Used for Key Encryption
The following Header Parameters are used for both algorithms defined
for key encryption.
2.2.1. "iv" (Initialization Vector) Header Parameter
The "iv" (initialization vector) Header Parameter value is the
base64url-encoded representation of the 96-bit or 192-bit IV value
used for the key encryption operation. This Header Parameter MUST be
present and MUST be understood and processed by implementations when
these algorithms are used.
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2.2.2. "tag" (Authentication Tag) Header Parameter
The "tag" (authentication tag) Header Parameter value is the
base64url-encoded representation of the 128-bit Authentication Tag
value resulting from the key encryption operation. This Header
Parameter MUST be present and MUST be understood and processed by
implementations when these algorithms are used.
3. Key Agreement with Elliptic Curve Diffie-Hellman Ephemeral Static
This section defines the specifics of key agreement with Elliptic
Curve Diffie-Hellman Ephemeral Static [RFC6090], in combination with
the Concat KDF, as defined in Section 5.8.2.1 of NIST.800-56A [1] for
use as a symmetric key to wrap the CEK with the "C20PKW", or
"XC20PKW" algorithms, in the Key Agreement with Key Wrapping mode.
This mode is used exactly as defined in Section 4.6 of RFC7518 [2],
except that the combined key wrapping algorithms are the ones
indicated in this document. All headers pertaining to both the ECDH-
ES and key wrapping components ("iv",' "tag", "epk", "apu", "apv")
have the same meaning and requirement as in their original
definitions.
The following "alg" (algorithm) Header Parameter values are used to
indicate that the JWE Encrypted Key is the result of encrypting the
CEK using the corresponding algorithm:
+-----------------+-------------------------------------------------+
| "alg" value | Key Management Algorithm |
+-----------------+-------------------------------------------------+
| ECDH-ES+C20PKW | ECDH-ES using Concat KDF and CEK wrapped with |
| | C20PKW |
| ECDH-ES+XC20PKW | ECDH-ES using Concat KDF and CEK wrapped with |
| | XC20PKW |
+-----------------+-------------------------------------------------+
4. Content Encryption
4.1. Algorithms
This section defines the specifics of performing authenticated
encryption with ChaCha20-Poly1305.
The CEK is used as the encryption key.
Use of an IV is REQUIRED with this algorithm.
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The following "enc" (encryption algorithm) Header Parameter values
are used to indicate that the JWE Ciphertext and JWE Authentication
Tag values have been computed using the corresponding algorithm and
IV size:
+-------------------------+----------+-------------+
| Algorithm | IV size | "alg" value |
+-------------------------+----------+-------------+
| AEAD_CHACHA20_POLY1305 | 96 bits | C20P |
| AEAD_XCHACHA20_POLY1305 | 192 bits | XC20P |
+-------------------------+----------+-------------+
5. IANA Considerations
The following is added to the "JSON Web Signature and Encryption
Algorithms" registry:
o Algorithm Name: "C20PKW"
o Algorithm Description: Key wrapping with ChaCha20-Poly1305
o Algorithm Usage Location(s): "alg"
o JOSE Implementation Requirements: Optional
o Change Controller: IESG
o Specification Document(s): Section 2 of [RFC-THIS]
o Algorithm Analysis Documents(s): [RFC8439]
o Algorithm Name: "XC20PKW"
o Algorithm Description: Key wrapping with XChaCha20-Poly1305
o Algorithm Usage Location(s): "alg"
o JOSE Implementation Requirements: Optional
o Change Controller: IESG
o Specification Document(s): Section 2 of [RFC-THIS]
o Algorithm Analysis Documents(s): [I-D.irtf-cfrg-xchacha]
o Algorithm Name: "ECDH-ES+C20PKW"
o Algorithm Description: ECDH-ES using Concat KDF and "C20PKW"
wrapping
o Algorithm Usage Location(s): "alg"
o JOSE Implementation Requirements: Optional
o Change Controller: IESG
o Specification Document(s): Section 3 of [RFC-THIS]
o Algorithm Analysis Documents(s): n/a
o Algorithm Name: "ECDH-ES+XC20PKW"
o Algorithm Description: ECDH-ES using Concat KDF and "XC20PKW"
wrapping
o Algorithm Usage Location(s): "alg"
o JOSE Implementation Requirements: Optional
o Change Controller: IESG
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o Specification Document(s): Section 3 of [RFC-THIS]
o Algorithm Analysis Documents(s): n/a
o Algorithm Name: "C20P"
o Algorithm Description: ChaCha20-Poly1305
o Algorithm Usage Location(s): "enc"
o JOSE Implementation Requirements: Optional
o Change Controller: IESG
o Specification Document(s): Section 4 of [RFC-THIS]
o Algorithm Analysis Documents(s): [RFC8439]
o Algorithm Name: "XC20P"
o Algorithm Description: ChaCha20-Poly1305
o Algorithm Usage Location(s): "enc"
o JOSE Implementation Requirements: Optional
o Change Controller: IESG
o Specification Document(s): Section 4 of [RFC-THIS]
o Algorithm Analysis Documents(s): [I-D.irtf-cfrg-xchacha]
6. References
6.1. Normative References
[I-D.irtf-cfrg-xchacha]
Arciszewski, S., "XChaCha: eXtended-nonce ChaCha and
AEAD_XChaCha20_Poly1305", draft-irtf-cfrg-xchacha-01 (work
in progress), July 2019.
[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>.
[RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
Curve Cryptography Algorithms", RFC 6090,
DOI 10.17487/RFC6090, February 2011,
<https://www.rfc-editor.org/info/rfc6090>.
[RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
RFC 7516, DOI 10.17487/RFC7516, May 2015,
<https://www.rfc-editor.org/info/rfc7516>.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/RFC7517, May 2015,
<https://www.rfc-editor.org/info/rfc7517>.
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[RFC7638] Jones, M. and N. Sakimura, "JSON Web Key (JWK)
Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September
2015, <https://www.rfc-editor.org/info/rfc7638>.
[RFC8439] Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
Protocols", RFC 8439, DOI 10.17487/RFC8439, June 2018,
<https://www.rfc-editor.org/info/rfc8439>.
6.2. URIs
[1] https://csrc.nist.gov/publications/detail/sp/800-56a/rev-3/final
[2] https://tools.ietf.org/html/rfc7518#section-4.6
Appendix A. Example using XC20PKW
*Considering the payload of "Hello World!" (Base64URL):*
SGVsbG8gV29ybGQh
*We begin by generating the XChacha20-Poly1309 content encryption key
(Base64URL):*
la2knCeFPAvUE2IVPm-RNrwj4UrHffLU6Y1tx3d5T1Q
*We follow by encrypting the CEK using XChacha20-Poly1309 itself. We
generate a new key and a nonce:*
KEK (Base64URL)
Rpv7sxPJYeNjKr-L8gPrKtQLHX-1dDuqtJuriVQ0eUY
Nonce (Base64URL)
LuNNS5RAagkOQVewQOLRp9noXET_YsPX
*Using those parameters, we end up with the following output from
XChacha20-Poly1309:*
Ciphertext (Base64URL)
K-kXEFjmSsjKzU91
Tag (Base64URL)
VT2Z9a93JFe2om2gboUz4g
*We then construct the following JWE header:*
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{"alg":"XC20PKW","enc":"XC20P","iv":"LuNNS5RAagkOQVewQOLRp9noXET
_YsPX","tag":"VT2Z9a93JFe2om2gboUz4g"}
*The next step is to prepare the content encryption:*
AAD (Base64URL)
eyJhbGciOiJYQzIwUEtXIiwiZW5jIjoiWEMyMFAiLCJpdiI6Ikx1Tk5TNVJBYWdr
T1FWZXdRT0xScDlub1hFVF9Zc1BYIiwidGFnIjoiVlQyWjlhOTNKRmUyb20yZ2Jv
VXo0ZyJ9
Key (generated earlier):
la2knCeFPAvUE2IVPm-RNrwj4UrHffLU6Y1tx3d5T1Q
Nonce (Base64URL)
LHs6vru3ggyuAzgT2UJkWyqJuZSv0Gae
*We then encrypt the payload with XChacha20-Poly1309 using the
previous parameters, which results in the following output:*
Ciphertext (Base64URL)
QgxRd4qQrkQNaEK3
Tag (Base64URL)
aQDs_RkdWabvzmxYEnoShg
*Lastly, we combine all the previous outputs to form the following
JWE:*
eyJhbGciOiJYQzIwUEtXIiwiZW5jIjoiWEMyMFAiLCJpdiI6Ikx1Tk5TNVJBYWdr
T1FWZXdRT0xScDlub1hFVF9Zc1BYIiwidGFnIjoiVlQyWjlhOTNKRmUyb20yZ2Jv
VXo0ZyJ9.K-kXEFjmSsjKzU91.LHs6vru3ggyuAzgT2UJkWyqJuZSv0Gae.QgxRd
4qQrkQNaEK3.aQDs_RkdWabvzmxYEnoShg
Appendix B. Example using ECDH-ES+XC20PKW
*Considering the payload of "Hello World!" (Base64URL):*
SGVsbG8gV29ybGQh
*We begin by generating the XChacha20-Poly1309 content encryption key
(Base64URL):*
O2-TuP5Qz_ab6N61LhVS6asFdN_X5zF0YhJ6Df0vtoE
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*We follow by encrypting the CEK using XChacha20-Poly1309 itself
following a key agreement. We generate a new key pair:*
Private X (Base64URL)
OtbkdOjp6SIgQ-TMXlqg48Ds8ycsSCxadJrjCurCcSM
Public X (Base64URL)
xxXXpDLvS0z-Zlx5J6dsVPPVonYufe9zTKfat0dEryM
*Using the recipient public key, we generate a shared secret*
Recipient PK (Base64URL)
8llBJmFOkoFO8TYhFyDFm90Z8c6ytiD18wUgM5alCHY
Shared Secret (Base64URL)
llX-1dAQU6BiuTDUq4DgRy9Ob-1zoLp-1hvmKa8baGk
*We can now derive a KEK:*
APU (Base64URL)
Q2tkNDNqSkZNb2FHeGVJZW9FUHgtNF9SYlNmLWd1T19MRHpvbDhrLWFnM2NELXhm
dzdWX1IzM0lXVHRDZ0NqVmhmWTVQa29aT3AyTGwxZTR5ZWZ4d2c
KEK (Base64URL)
jPC4ybPvJ-FF4qz7hYiHDxr7XGQdQCMDjWaQ-y_MJfQ
*We can now perform XChacha20-Poly1309 on the CEK using a new random
nonce:*
Nonce (Base64URL)
1Ef_Hs3NdFIujh9-uZEYLz4N_b1K1CJl
Ciphertext (Base64URL)
mzHMc5XlqW-jkGP4
Tag (Base64URL)
G8A4JnNmsG2wgvQh6Q5A8g
*We then construct the following JWE header:*
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{"alg":"ECDH-ES+XC20PKW","enc":"XC20P","iv":"1Ef_Hs3NdFIujh9-uZE
YLz4N_b1K1CJl","tag":"G8A4JnNmsG2wgvQh6Q5A8g","apu":"Q2tkNDNqSkZ
Nb2FHeGVJZW9FUHgtNF9SYlNmLWd1T19MRHpvbDhrLWFnM2NELXhmdzdWX1IzM0l
XVHRDZ0NqVmhmWTVQa29aT3AyTGwxZTR5ZWZ4d2c","epk":{"typ":"OKP","cr
v":"X25519","x":"xxXXpDLvS0z-Zlx5J6dsVPPVonYufe9zTKfat0dEryM"}}
*The next step is to prepare the content encryption:*
AAD (Base64URL)
eyJhbGciOiJFQ0RILUVTK1hDMjBQS1ciLCJlbmMiOiJYQzIwUCIsIml2IjoiMUVm
X0hzM05kRkl1amg5LXVaRVlMejROX2IxSzFDSmwiLCJ0YWciOiJHOEE0Sm5ObXNH
MndndlFoNlE1QThnIiwiYXB1IjoiUTJ0a05ETnFTa1pOYjJGSGVHVkpaVzlGVUhn
dE5GOVNZbE5tTFdkMVQxOU1SSHB2YkRockxXRm5NMk5FTFhobWR6ZFdYMUl6TTBs
WFZIUkRaME5xVm1obVdUVlFhMjlhVDNBeVRHd3haVFI1WldaNGQyYyIsImVwayI6
eyJ0eXAiOiJPS1AiLCJjcnYiOiJYMjU1MTkiLCJ4IjoieHhYWHBETHZTMHotWmx4
NUo2ZHNWUFBWb25ZdWZlOXpUS2ZhdDBkRXJ5TSJ9fQ
Key (generated earlier):
O2-TuP5Qz_ab6N61LhVS6asFdN_X5zF0YhJ6Df0vtoE
Nonce (Base64URL)
okZz0AJz-PfUL4OGjioPLsg6-siwyq2I
*We then encrypt the payload with XChacha20-Poly1309 using the
previous parameters, which results in the following output:*
Ciphertext (Base64URL)
yxpuuXB7DcXBlyVE
Tag (Base64URL)
IwvDEC8hxltfzidjmUKeMg
*Lastly, we combine all the previous outputs to form the following
JWE:*
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eyJhbGciOiJFQ0RILUVTK1hDMjBQS1ciLCJlbmMiOiJYQzIwUCIsIml2IjoiMUVm
X0hzM05kRkl1amg5LXVaRVlMejROX2IxSzFDSmwiLCJ0YWciOiJHOEE0Sm5ObXNH
MndndlFoNlE1QThnIiwiYXB1IjoiUTJ0a05ETnFTa1pOYjJGSGVHVkpaVzlGVUhn
dE5GOVNZbE5tTFdkMVQxOU1SSHB2YkRockxXRm5NMk5FTFhobWR6ZFdYMUl6TTBs
WFZIUkRaME5xVm1obVdUVlFhMjlhVDNBeVRHd3haVFI1WldaNGQyYyIsImVwayI6
eyJ0eXAiOiJPS1AiLCJjcnYiOiJYMjU1MTkiLCJ4IjoieHhYWHBETHZTMHotWmx4
NUo2ZHNWUFBWb25ZdWZlOXpUS2ZhdDBkRXJ5TSJ9fQ.mzHMc5XlqW-jkGP4.okZz
0AJz-PfUL4OGjioPLsg6-siwyq2I.yxpuuXB7DcXBlyVE.IwvDEC8hxltfzidjmU
KeMg
Author's Address
Guillaume Amringer
Canada
Email: g.amringer@gmail.com
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