Internet Engineering Task Force A. Rundgren, Ed.
Internet-Draft Independent
Intended status: Informational 18 March 2025
Expires: 19 September 2025
Universal CBOR (U-CBOR)
draft-rundgren-universal-cbor-06
Abstract
This document defines Universal CBOR (U-CBOR), a strict subset of
CBOR (RFC 8949) intended to serve as a viable replacement for JSON in
computationally advanced systems like Internet browsers, mobile
phones, and Web servers. To foster interoperability, deterministic
encoding is mandated. Furthermore, the document outlines how
deterministic encoding combined with enhanced CBOR tools, enable
cryptographic methods like signing and hashing, to optionally use
"raw" (non-wrapped) CBOR data as input. This document mainly targets
CBOR tool developers.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 19 September 2025.
Copyright Notice
Copyright (c) 2025 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 (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
Rundgren Expires 19 September 2025 [Page 1]
Internet-Draft U-CBOR March 2025
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Common Definitions . . . . . . . . . . . . . . . . . . . 3
2. Detailed Description . . . . . . . . . . . . . . . . . . . . 3
2.1. Supported CBOR Objects . . . . . . . . . . . . . . . . . 4
2.2. Deterministic Encoding Scheme . . . . . . . . . . . . . . 5
2.3. CBOR Tool Requirements . . . . . . . . . . . . . . . . . 6
2.3.1. Protocol Primitives Support . . . . . . . . . . . . . 7
2.3.2. Media Type . . . . . . . . . . . . . . . . . . . . . 8
2.3.3. Diagnostic Notation Support . . . . . . . . . . . . . 8
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
4. Security Considerations . . . . . . . . . . . . . . . . . . . 12
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1. Normative References . . . . . . . . . . . . . . . . . . 12
5.2. Informative References . . . . . . . . . . . . . . . . . 12
Appendix A. Deterministic Encoding Samples . . . . . . . . . . . 14
A.1. Integers . . . . . . . . . . . . . . . . . . . . . . . . 14
A.2. Floating Point Numbers . . . . . . . . . . . . . . . . . 16
A.3. Invalid Encodings . . . . . . . . . . . . . . . . . . . . 20
Appendix B. Enveloped Signatures . . . . . . . . . . . . . . . . 22
B.1. Sample Signature . . . . . . . . . . . . . . . . . . . . 22
B.1.1. Unsigned Data . . . . . . . . . . . . . . . . . . . . 22
B.1.2. Signature Process . . . . . . . . . . . . . . . . . . 23
B.1.3. Validation Process . . . . . . . . . . . . . . . . . 24
B.1.4. Example Parameters . . . . . . . . . . . . . . . . . 25
B.2. Code Example . . . . . . . . . . . . . . . . . . . . . . 25
Appendix C. Supporting Existing Systems . . . . . . . . . . . . 26
Appendix D. Compatible Online Tools . . . . . . . . . . . . . . 27
Appendix E. Compatible Implementations . . . . . . . . . . . . . 27
Document History . . . . . . . . . . . . . . . . . . . . . . . . 28
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 28
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 28
1. Introduction
The Universal CBOR (U-CBOR) specification is based on CBOR [RFC8949].
While there are different ways you can encode certain CBOR objects,
this is non-trivial to support in general purpose platform-based
tools, not to mention the limited utility of such measures. To cope
with this, U-CBOR defines a specific (non-variant) encoding scheme,
aka "Deterministic Encoding". The selected encoding scheme is
believed to be _compatible_ with most existing _systems_ using CBOR.
Rundgren Expires 19 September 2025 [Page 2]
Internet-Draft U-CBOR March 2025
See also Appendix C.
U-CBOR is intended to be agnostic with respect to programming
languages.
By combining the compact binary representation and the rich set of
data types offered by CBOR, with a deterministic encoding scheme,
U-CBOR could for _new designs_, serve as viable alternative to JSON
[RFC8259]. Although the mandated encoding scheme is deployable in
[CONSTRAINED] environments, the primary target is rather general-
purpose computing platforms like mobile phones and Web servers.
However, for unleashing the full power of deterministic encoding, the
ability to perform cryptographic operations on "raw" (non-wrapped)
CBOR data, compliant U-CBOR tools need additional functionality. See
also Appendix B.
Section 2 contains the actual specification.
1.1. Requirements Language
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.
1.2. Common Definitions
* This document uses the conventions defined in CDDL [RFC8610] for
expressing the type of CBOR [RFC8949] data items.
* Examples showing CBOR data, are expressed in "diagnostic notation"
as defined in Section 8 of [RFC8949].
* The term "CBOR object" is equivalent to "CBOR data item" used in
[RFC8949].
* The term "Universal CBOR" is in this document abbreviated to
"U-CBOR".
2. Detailed Description
This section describes the three pillars that U-CBOR relies on.
Rundgren Expires 19 September 2025 [Page 3]
Internet-Draft U-CBOR March 2025
2.1. Supported CBOR Objects
The following table shows the CBOR subset supported by U-CBOR:
+==============+========================================+
| CDDL | Description |
+==============+========================================+
| int | Integer |
+--------------+----------------------------------------+
| bigint | Big integer |
+--------------+----------------------------------------+
| float | 16-, 32-, and 64-bit [IEEE754] numbers |
+--------------+----------------------------------------+
| tstr | Text string encoded as UTF-8 [RFC3629] |
+--------------+----------------------------------------+
| bstr | Byte string |
+--------------+----------------------------------------+
| bool | Boolean true and false |
+--------------+----------------------------------------+
| null | Represents a null object |
+--------------+----------------------------------------+
| [] | Array |
+--------------+----------------------------------------+
| {} | Map |
+--------------+----------------------------------------+
| #6.nnn(type) | Tagged data |
+--------------+----------------------------------------+
Table 1: Supported CBOR Objects
Conforming implementations (of course) only have to implement the
U-CBOR types required by the targeted application(s).
Although extensions are imaginable (like supporting all "simple"
types), extensions will most likely cause _interoperability issues_
and are thus NOT RECOMMENDED. In addition, the mandated CBOR subset
is compatible with most computer languages and platforms. Compared
to the current state-of-the-art, JSON [RFC8259], the availability of
bigint, bstr, and "tagged data" represent major improvements.
However, nothing prevents developers from at the application (API)
level, through mapping concepts, support additional, "virtual" data
types, analogous to how you map an application's data model to the
set of data types available, be it a data interchange format, a
database, or a programming language.
OpenAPI [OPENAPI] is an example of an API which defines data types
through mapping.
Rundgren Expires 19 September 2025 [Page 4]
Internet-Draft U-CBOR March 2025
2.2. Deterministic Encoding Scheme
In U-CBOR deterministic encoding is _mandatory_. The encoding scheme
adheres to Section 4.2 of [RFC8949], but adds a few constraints
(denoted by RFC+), where the RFC offers choices. The following list
contains a summary of the U-CBOR deterministic encoding rules:
* RFC+: Floating-point and integer objects MUST be treated as
_distinct types_ regardless of their numeric value. This is
compliant with Rule 2 in Section 4.2.2 of [RFC8949].
* RFC: Integers, represented by the int and bigint types, MUST use
the int type if the value is between -2^64 and 2^64-1, otherwise
the bigint type MUST be used. Appendix A.1 features a list of
compliant integer sample values.
* RFC: Floating-point numbers MUST always use the shortest [IEEE754]
variant that preserves the precision of the original value.
Appendix A.2 features a list of compliant floating-point sample
values.
* RFC+: NaN "signaling" items (like f97e01), MUST be _rejected_.
* RFC: Map keys MUST be sorted in the bytewise lexicographic order
of their deterministic encoding. Duplicate keys MUST be
_rejected_. Somewhat surprisingly the following represents a
properly sorted map:
{
"a": ... ,
"b": ... ,
"aa": ...
}
* RFC+: Since CBOR encodings according to this specification
maintain uniqueness, there are no specific restrictions or tests
needed in order to determine map key equivalence. As an (extreme)
example, the floating-point numbers 0.0 and -0.0, and the integer
number 0 could represent the distinct keys f90000, f98000, and 00
respectively.
* RFC: Indefinite length objects MUST be _rejected_.
Rundgren Expires 19 September 2025 [Page 5]
Internet-Draft U-CBOR March 2025
2.3. CBOR Tool Requirements
An important feature that deterministic encoding brings to the table
is that wrapping CBOR data to be signed in bstr objects, like
specified by COSE in Section 2 of [RFC9052], no longer is a
prerequisite. That is, cryptographic operations can _optionally_ be
performed on "raw" CBOR data. Turn to Appendix B for an example of
an application depending on such features.
However, to make this a reality, the following functionality MUST be
provided by CBOR tools compliant with this specification:
* Decoded CBOR primitives MUST remain _immutable_, regardless if
they are stand-alone or being a part of a tagged object like
bigfloat (see Section 3.4.4 of [RFC8949]).
* It MUST be possible to find out the type of a CBOR object,
_before_ it is accessed.
* It MUST be possible to _add_, _delete_, and _update_ the contents
of CBOR map and array objects, of decoded CBOR data.
* It MUST be possible to _reserialize_ decoded CBOR data, be it
updated or not.
* Irrespective of if CBOR data was decoded, updated, or created
programmatically, deterministic encoding MUST be maintained.
* Invalid or unsupported CBOR constructs, as well as CBOR data not
adhering to the deterministic encoding scheme MUST be _rejected_.
See also Appendix C and Appendix A.3.
As a consequence of these rules, CBOR data and application /
platform-level data, MUST be _separated_ for cases where
_reserialization_ could present a problem, like in this Chrome
browser console example:
> let date = new Date('2025-03-02T13:08:55.0001+03:00');
> date.toISOString()
'2025-03-02T10:08:55.000Z'
How this separation actually is accomplished is out of scope for this
specification. However, _encapsulation_ of CBOR data in _high-
level_, and _self-rendering objects_, represents an established
method, featured in similar tools for ASN.1. The code in
Appendix B.2 shows an example that _updates_ and _reserializes_
decoded CBOR data.
Rundgren Expires 19 September 2025 [Page 6]
Internet-Draft U-CBOR March 2025
2.3.1. Protocol Primitives Support
To facilitate cross-platform _protocol interoperability_,
implementers of U-CBOR compatible tools SHOULD include _decoder_ API
support for the following primitives:
+==============+===========+==============================+======+
| CDDL | Primitive | Description | Note |
+==============+===========+==============================+======+
| int | Int8 | 8-bit signed integer | 1 |
+--------------+-----------+------------------------------+------+
| uint | Uint8 | 8-bit unsigned integer | 1 |
+--------------+-----------+------------------------------+------+
| int | Int16 | 16-bit signed integer | 1 |
+--------------+-----------+------------------------------+------+
| uint | Uint16 | 16-bit unsigned integer | 1 |
+--------------+-----------+------------------------------+------+
| int | Int32 | 32-bit signed integer | 1 |
+--------------+-----------+------------------------------+------+
| uint | Uint32 | 32-bit unsigned integer | 1 |
+--------------+-----------+------------------------------+------+
| int | Int64 | 64-bit signed integer | 1 |
+--------------+-----------+------------------------------+------+
| uint | Uint64 | 64-bit unsigned integer | 1 |
+--------------+-----------+------------------------------+------+
| int / bigint | BigInt | Integer of arbitrary size | 2 |
+--------------+-----------+------------------------------+------+
| float16 | Float16 | 16-bit floating-point number | 3 |
+--------------+-----------+------------------------------+------+
| float16 / | Float32 | 32-bit floating-point number | 3 |
| float32 | | | |
+--------------+-----------+------------------------------+------+
| float | Float64 | 64-bit floating-point number | |
+--------------+-----------+------------------------------+------+
| bool | Boolean | Boolean | |
+--------------+-----------+------------------------------+------+
| null | Null | Null | 4 |
+--------------+-----------+------------------------------+------+
| See note | EpochTime | Time-object expressed as a | 5 |
| | | number | |
+--------------+-----------+------------------------------+------+
| See note | DateTime | Time-object expressed as a | 5 |
| | | text string | |
+--------------+-----------+------------------------------+------+
Table 2: Protocol Primitives Support
Rundgren Expires 19 September 2025 [Page 7]
Internet-Draft U-CBOR March 2025
1. Range testing MUST be performed using the traditional ranges for
_unsigned_ respectively _two-complement_ numbers. That is, a
hypothetical getUint8() MUST reject numbers outside of 0 to 255,
whereas a hypothetical getInt8(), MUST reject numbers outside of
-128 to 127.
2. Note that a hypothetical getBigInt() MUST also accept CBOR int
objects since int is used for integers that fit in CBOR major
type 0 and 1 objects. See also Appendix A.1 and Appendix C.
3. Some platforms do not natively support float32 and/or float16.
In this case a hypothetical getFloat16() would need to use a
bigger floating-point type for the return value.
Note that a hypothetical getFloat16() MUST reject encountered
Float32 and Float64 objects. See also Appendix C.
4. Since a CBOR null typically represents the absence of a value, a
decoder MUST provide a test-function, like isNull().
5. Since CBOR does not feature a native-level time-object,
Section 3.4 of [RFC8949] introduces two variants of time-objects
using the CBOR tags 0 and 1. The time-objects SHOULD also be
supported without the tag construct.
If a call does not match the underlying CDDL type, the call MUST be
rejected,
Due to considerable variations between platforms, corresponding
_encoder_ API support does not appear to be meaningful to specify in
detail: Java doesn't have built-in support for unsigned integers,
whereas JavaScript requires the use of the JavaScript BigInt type for
dealing with 64-bit integers.
2.3.2. Media Type
Protocols building on U-CBOR, are RECOMMENDED using the media type:
application/cbor.
2.3.3. Diagnostic Notation Support
Compliant U-CBOR implementations SHOULD include support for _bi-
directional_ diagnostic notation, to facilitate:
* Human-centric debugging and logging
* Easy creation of test and configuration data
Rundgren Expires 19 September 2025 [Page 8]
Internet-Draft U-CBOR March 2025
The supported notation is compliant with a subset of Section 8 of
[RFC8949] (b32' and encoding indicators were left out), but adds a
few items to make diagnostic notation slightly more adapted for
parsing, like single-line comments:
+=========+==============================+==================+=======+
| CDDL | Syntax | Description | Notes |
+=========+==============================+==================+=======+
| | / _comment text_ / |Multi-line | 6 |
| | |comment. Multi- | |
| | |line comments are | |
| | |treated as | |
| | |whitespace and | |
| | |may thus also be | |
| | |used _between_ | |
| | |CBOR objects. | |
+---------+------------------------------+------------------+-------+
| | # _comment text_ |Single-line | 6 |
| | |comment. Single- | |
| | |line comments are | |
| | |terminated by a | |
| | |newline character | |
| | |('\n') or EOF. | |
| | |Single-line | |
| | |comments may also | |
| | |terminate lines | |
| | |holding regular | |
| | |CBOR items. | |
+---------+------------------------------+------------------+-------+
| int / | {_sign_}{0b|0o|0x}_n_ |Arbitrary sized | 1, 2 |
| bigint | |integers without | |
| | |fractional | |
| | |components or | |
| | |exponents. See | |
| | |also CBOR integer | |
| | |encoding. For | |
| | |_input_ data in | |
| | |diagnostic | |
| | |notation, binary, | |
| | |octal, and | |
| | |hexadecimal | |
| | |notation is also | |
| | |supported by | |
| | |prepending | |
| | |numbers with 0b, | |
| | |0o, and 0x | |
| | |respectively. | |
| | |The latter also | |
Rundgren Expires 19 September 2025 [Page 9]
Internet-Draft U-CBOR March 2025
| | |permit arbitrary | |
| | |insertions of '_' | |
| | |characters | |
| | |between digits to | |
| | |enable grouping | |
| | |of data like | |
| | |0b100_000000001. | |
+---------+------------------------------+------------------+-------+
|float16 /| {_sign_}_n_._n_{e±_n_} |Floating point | 1, 2 |
|float32 /| |values MUST | |
| float64 | |include a decimal | |
| | |point and at | |
| | |least one | |
| | |fractional digit, | |
| | |whereas exponents | |
| | |are _optional_. | |
+---------+------------------------------+------------------+-------+
| float16 | NaN |Not a number. | |
+---------+------------------------------+------------------+-------+
| float16 | {_sign_}Infinity |Infinity. | 2 |
+---------+------------------------------+------------------+-------+
| bstr | h'_hex data_' |Byte data | 3 |
| | |provided in | |
| | |hexadecimal | |
| | |notation. Each | |
| | |byte MUST be | |
| | |represented by | |
| | |two hexadecimal | |
| | |digits. | |
+---------+------------------------------+------------------+-------+
| bstr | b64'_base64 data_' |Byte data | 3, 6 |
| | |provided in | |
| | |base64 or | |
| | |base64URL | |
| | |notation. | |
| | |Padding with '=' | |
| | |characters is | |
| | |_optional_. | |
+---------+------------------------------+------------------+-------+
| bstr | '_text_' |Byte data |4, 5, 6|
| | |provided as UTF-8 | |
| | |encoded text. | |
+---------+------------------------------+------------------+-------+
| bstr | << {_object_, }... >> |Construct holding | 6 |
| | |zero or more | |
| | |comma-separated | |
| | |CBOR objects | |
| | |which are | |
Rundgren Expires 19 September 2025 [Page 10]
Internet-Draft U-CBOR March 2025
| | |subsequently | |
| | |wrapped in a | |
| | |byte-string. | |
+---------+------------------------------+------------------+-------+
| tstr | "_text_" |UTF-8 encoded | 4, 5 |
| | |text-string. | |
+---------+------------------------------+------------------+-------+
| bool | true | false |Boolean value. | |
+---------+------------------------------+------------------+-------+
| null | null |Null value. | |
+---------+------------------------------+------------------+-------+
| [] | [ {_object_, }... ] |Array with zero | |
| | |or more comma- | |
| | |separated CBOR | |
| | |objects. | |
+---------+------------------------------+------------------+-------+
| {} | { {_key_:_value_, }... } |Map with zero or | |
| | |more comma- | |
| | |separated key/ | |
| | |value pairs. | |
| | |Keys and values | |
| | |are expressed as | |
| | |CBOR objects. | |
+---------+------------------------------+------------------+-------+
| #6.n | _n_( _object_ ) |Tag holding a | 1 |
| | |CBOR object. | |
+---------+------------------------------+------------------+-------+
Table 3: Diagnostic Notation Support
1. The letter _n_ in the Syntax column denotes one or more digits.
2. The optional {_sign_} must be a single hyphen ('-') character.
3. _Input only_: between the quotes, the whitespace characters (' ',
'\t', '\r', '\n') are _ignored_.
4. _Input only_: the control characters ('\t' and '\n') inside of
string quotes _become a part of the text_. For normalizing line
terminators, a single '\r' or the combination '\r\n' are
rewritten as '\n'. To _avoid_ getting newline characters ('\n')
included in multi-line text strings, a _line continuation marker_
consisting of a backslash ('\') immediately preceding the newline
may be used.
5. Text strings may also include JavaScript compatible escape
sequences ('\'', '\"', '\\', '\b', '\f', '\n', '\r', '\t',
'\u_hhhh_').
Rundgren Expires 19 September 2025 [Page 11]
Internet-Draft U-CBOR March 2025
6. _Input only_.
3. IANA Considerations
This memo includes no request to IANA.
4. Security Considerations
All is good 😸
U-CBOR does not introduce security issues beyond what is already
applicable to [RFC8949]. Applications may certainly add security
issues, but these are out of scope for this specification.
5. References
5.1. 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/info/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/info/rfc8174>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/info/rfc3629>.
[IEEE754] IEEE, "IEEE Standard for Floating-Point Arithmetic", IEEE
Std 754-2019, DOI 10.1109/IEEESTD.2019.8766229,
<https://ieeexplore.ieee.org/document/8766229>.
5.2. Informative References
Rundgren Expires 19 September 2025 [Page 12]
Internet-Draft U-CBOR March 2025
[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/info/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/info/rfc9053>.
[RFC8785] Rundgren, A., Jordan, B., and S. Erdtman, "JSON
Canonicalization Scheme (JCS)", RFC 8785,
DOI 10.17487/RFC8785, June 2020,
<https://www.rfc-editor.org/info/rfc8785>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[CSF] Rundgren, A., "CBOR Signature Format (CSF)",
<https://cyberphone.github.io/javaapi/org/webpki/cbor/doc-
files/signatures.html>.
[CEF] Rundgren, A., "CBOR Encryption Format (CEF)",
<https://cyberphone.github.io/javaapi/org/webpki/cbor/doc-
files/encryption.html>.
[COTX] Rundgren, A., "CBOR Object Type Extension (COTX)",
<https://www.ietf.org/archive/id/draft-rundgren-cotx-
04.html>.
[CONSTRAINED]
"D-CBOR for Constrained Devices",
<https://github.com/cyberphone/D-CBOR/blob/main/d-cbor-4-
constrained-devices.md>.
[NODE.JS] "Node.js - JavaScript server", <https://nodejs.org/>.
[CBOR.JS] "CBOR.js - CBOR for JavaScript",
<https://github.com/cyberphone/CBOR.js>.
[CSF-LAB] "Online CBOR and CSF test tool",
<https://test.webpki.org/csf-lab>.
[PLAYGROUND]
"Online CBOR testing tool",
<https://cyberphone.github.io/CBOR.js/doc/
playground.html>.
Rundgren Expires 19 September 2025 [Page 13]
Internet-Draft U-CBOR March 2025
[OPENKEYSTORE]
"Java library supporting JSON, CBOR, and Crypto",
<https://github.com/cyberphone/openkeystore>.
[ANDROID-CBOR]
"Android/Java library supporting CBOR and Crypto",
<https://github.com/cyberphone/android-cbor>.
[OPENAPI] "The OpenAPI Initiative", <https://openapis.org/>.
[CREDENTIALS]
Sporny (et al), M., "Verifiable Credential Data Integrity
1.0", 2025, <https://www.w3.org/TR/vc-data-integrity/>.
[CBOR.ME] Bormann, C., "Online CBOR testing tool",
<https://cbor.me/>.
[ECMASCRIPT]
Ecma International, "ECMAScript® 2024 Language
Specification", Standard ECMA-262, 15th Edition, June
2024, <https://www.ecma-
international.org/publications/standards/Ecma-262.htm>.
[WALLET] Rundgren, A., "Defensive publication: Partial Encryption,
Full Signature", <https://cyberphone.github.io/doc/
defensive-publications/partial-encryption-full-
signature.pdf>.
Appendix A. Deterministic Encoding Samples
A.1. Integers
This _normative_ section holds a selection of CBOR integer values,
with an emphasize on edge cases.
+=======================+========================+================+
| Value | CBOR Encoding | Description |
+=======================+========================+================+
| 0 | 00 | Smallest |
| | | positive |
| | | implicit int |
+-----------------------+------------------------+----------------+
| -1 | 20 | Smallest |
| | | negative |
| | | implicit int |
+-----------------------+------------------------+----------------+
| 23 | 17 | Largest |
| | | positive |
Rundgren Expires 19 September 2025 [Page 14]
Internet-Draft U-CBOR March 2025
| | | implicit int |
+-----------------------+------------------------+----------------+
| -24 | 37 | Largest |
| | | negative |
| | | implicit int |
+-----------------------+------------------------+----------------+
| 24 | 1818 | Smallest |
| | | positive one- |
| | | byte int |
+-----------------------+------------------------+----------------+
| -25 | 3818 | Smallest |
| | | negative one- |
| | | byte int |
+-----------------------+------------------------+----------------+
| 255 | 18ff | Largest |
| | | positive one- |
| | | byte int |
+-----------------------+------------------------+----------------+
| -256 | 38ff | Largest |
| | | negative one- |
| | | byte int |
+-----------------------+------------------------+----------------+
| 256 | 190100 | Smallest |
| | | positive two- |
| | | byte int |
+-----------------------+------------------------+----------------+
| -257 | 390100 | Smallest |
| | | negative two- |
| | | byte int |
+-----------------------+------------------------+----------------+
| 65535 | 19ffff | Largest |
| | | positive two- |
| | | byte int |
+-----------------------+------------------------+----------------+
| -65536 | 39ffff | Largest |
| | | negative two- |
| | | byte int |
+-----------------------+------------------------+----------------+
| 65536 | 1a00010000 | Smallest |
| | | positive four- |
| | | byte int |
+-----------------------+------------------------+----------------+
| -65537 | 3a00010000 | Smallest |
| | | negative four- |
| | | byte int |
+-----------------------+------------------------+----------------+
| 4294967295 | 1affffffff | Largest |
| | | positive four- |
Rundgren Expires 19 September 2025 [Page 15]
Internet-Draft U-CBOR March 2025
| | | byte int |
+-----------------------+------------------------+----------------+
| -4294967296 | 3affffffff | Largest |
| | | negative four- |
| | | byte int |
+-----------------------+------------------------+----------------+
| 4294967296 | 1b0000000100000000 | Smallest |
| | | positive |
| | | eight-byte int |
+-----------------------+------------------------+----------------+
| -4294967297 | 3b0000000100000000 | Smallest |
| | | negative |
| | | eight-byte int |
+-----------------------+------------------------+----------------+
| 18446744073709551615 | 1bffffffffffffffff | Largest |
| | | positive |
| | | eight-byte int |
+-----------------------+------------------------+----------------+
| -18446744073709551616 | 3bffffffffffffffff | Largest |
| | | negative |
| | | eight-byte int |
+-----------------------+------------------------+----------------+
| 18446744073709551616 | c249010000000000000000 | Smallest |
| | | positive |
| | | bigint |
+-----------------------+------------------------+----------------+
| -18446744073709551617 | c349010000000000000000 | Smallest |
| | | negative |
| | | bigint |
+-----------------------+------------------------+----------------+
Table 4: Integers
A.2. Floating Point Numbers
This _normative_ section holds a selection of [IEEE754] 16, 32, and
64-bit values, with an emphasize on edge cases.
The textual representation of the values is based on the
serialization method for the Number data type, defined by
[ECMASCRIPT] with one change: to comply with diagnostic notation
(section 8 of [RFC8949]), all values are expressed as floating-point
numbers. The rationale for using [ECMASCRIPT] serialization is
because it supposed to generate the shortest and most correct
representation of [IEEE754] numbers.
Rundgren Expires 19 September 2025 [Page 16]
Internet-Draft U-CBOR March 2025
+===========================+====================+==================+
| Value | CBOR Encoding | Description |
+===========================+====================+==================+
| 0.0 | f90000 | Zero |
+---------------------------+--------------------+------------------+
| -0.0 | f98000 | Negative |
| | | zero |
+---------------------------+--------------------+------------------+
| Infinity | f97c00 | Infinity |
+---------------------------+--------------------+------------------+
| -Infinity | f9fc00 | -Infinity |
+---------------------------+--------------------+------------------+
| NaN | f97e00 | NaN |
+---------------------------+--------------------+------------------+
| 5.960464477539063e-8 | f90001 | Smallest |
| | | positive |
| | | _subnormal_ |
| | | 16-bit float |
+---------------------------+--------------------+------------------+
| 0.00006097555160522461 | f903ff | Largest |
| | | positive |
| | | _subnormal_ |
| | | 16-bit float |
+---------------------------+--------------------+------------------+
| 0.00006103515625 | f90400 | Smallest |
| | | positive |
| | | 16-bit float |
+---------------------------+--------------------+------------------+
| 65504.0 | f97bff | Largest |
| | | positive |
| | | 16-bit float |
+---------------------------+--------------------+------------------+
| 1.401298464324817e-45 | fa00000001 | Smallest |
| | | positive |
| | | _subnormal_ |
| | | 32-bit float |
+---------------------------+--------------------+------------------+
| 1.1754942106924411e-38 | fa007fffff | Largest |
| | | positive |
| | | _subnormal_ |
| | | 32-bit float |
+---------------------------+--------------------+------------------+
| 1.1754943508222875e-38 | fa00800000 | Smallest |
| | | positive |
| | | 32-bit float |
+---------------------------+--------------------+------------------+
| 3.4028234663852886e+38 | fa7f7fffff | Largest |
| | | positive |
Rundgren Expires 19 September 2025 [Page 17]
Internet-Draft U-CBOR March 2025
| | | 32-bit float |
+---------------------------+--------------------+------------------+
| 5.0e-324 | fb0000000000000001 | Smallest |
| | | positive |
| | | _subnormal_ |
| | | 64-bit float |
+---------------------------+--------------------+------------------+
| 2.225073858507201e-308 | fb000fffffffffffff | Largest |
| | | positive |
| | | _subnormal_ |
| | | 64-bit float |
+---------------------------+--------------------+------------------+
| 2.2250738585072014e-308 | fb0010000000000000 | Smallest |
| | | positive |
| | | 64-bit float |
+---------------------------+--------------------+------------------+
| 1.7976931348623157e+308 | fb7fefffffffffffff | Largest |
| | | positive |
| | | 64-bit float |
+---------------------------+--------------------+------------------+
| -0.0000033333333333333333 | fbbecbf647612f3696 | Randomly |
| | | selected |
| | | number |
+---------------------------+--------------------+------------------+
| 10.559998512268066 | fa4128f5c1 | -"- |
+---------------------------+--------------------+------------------+
| 10.559998512268068 | fb40251eb820000001 | Next in |
| | | succession |
+---------------------------+--------------------+------------------+
| 295147905179352830000.0 | fa61800000 | 2^68 |
| | | (diagnostic |
| | | notation |
| | | truncates |
| | | precision) |
+---------------------------+--------------------+------------------+
| 2.0 | f94000 | Number |
| | | without a |
| | | fractional |
| | | part |
+---------------------------+--------------------+------------------+
| -5.960464477539063e-8 | f98001 | Smallest |
| | | negative |
| | | _subnormal_ |
| | | 16-bit float |
+---------------------------+--------------------+------------------+
| -5.960464477539062e-8 | fbbe6fffffffffffff | Adjacent |
| | | smallest |
| | | negative |
Rundgren Expires 19 September 2025 [Page 18]
Internet-Draft U-CBOR March 2025
| | | _subnormal_ |
| | | 16-bit float |
+---------------------------+--------------------+------------------+
| -5.960464477539064e-8 | fbbe70000000000001 | -"- |
+---------------------------+--------------------+------------------+
| -5.960465188081798e-8 | fab3800001 | -"- |
+---------------------------+--------------------+------------------+
| 0.0000609755516052246 | fb3f0ff7ffffffffff | Adjacent |
| | | largest |
| | | _subnormal_ |
| | | 16-bit float |
+---------------------------+--------------------+------------------+
| 0.000060975551605224616 | fb3f0ff80000000001 | -"- |
+---------------------------+--------------------+------------------+
| 0.000060975555243203416 | fa387fc001 | -"- |
+---------------------------+--------------------+------------------+
| 0.00006103515624999999 | fb3f0fffffffffffff | Adjacent |
| | | smallest |
| | | 16-bit float |
+---------------------------+--------------------+------------------+
| 0.00006103515625000001 | fb3f10000000000001 | -"- |
+---------------------------+--------------------+------------------+
| 0.00006103516352595761 | fa38800001 | -"- |
+---------------------------+--------------------+------------------+
| 65503.99999999999 | fb40effbffffffffff | Adjacent |
| | | largest |
| | | 16-bit float |
+---------------------------+--------------------+------------------+
| 65504.00000000001 | fb40effc0000000001 | -"- |
+---------------------------+--------------------+------------------+
| 65504.00390625 | fa477fe001 | -"- |
+---------------------------+--------------------+------------------+
| 1.4012984643248169e-45 | fb369fffffffffffff | Adjacent |
| | | smallest |
| | | _subnormal_ |
| | | 32-bit float |
+---------------------------+--------------------+------------------+
| 1.4012984643248174e-45 | fb36a0000000000001 | -"- |
+---------------------------+--------------------+------------------+
| 1.175494210692441e-38 | fb380fffffbfffffff | Adjacent |
| | | largest |
| | | _subnormal_ |
| | | 32-bit float |
+---------------------------+--------------------+------------------+
| 1.1754942106924412e-38 | fb380fffffc0000001 | -"- |
+---------------------------+--------------------+------------------+
| 1.1754943508222874e-38 | fb380fffffffffffff | Adjacent |
| | | smallest |
Rundgren Expires 19 September 2025 [Page 19]
Internet-Draft U-CBOR March 2025
| | | 32-bit float |
+---------------------------+--------------------+------------------+
| 1.1754943508222878e-38 | fb3810000000000001 | -"- |
+---------------------------+--------------------+------------------+
| 3.4028234663852882e+38 | fb47efffffdfffffff | Adjacent |
| | | largest |
| | | 32-bit float |
+---------------------------+--------------------+------------------+
| 3.402823466385289e+38 | fb47efffffe0000001 | -"- |
+---------------------------+--------------------+------------------+
Table 5: Floating Point Numbers
A.3. Invalid Encodings
The following table holds a selection of valid CBOR objects, not
permitted by U-CBOR.
Rundgren Expires 19 September 2025 [Page 20]
Internet-Draft U-CBOR March 2025
+==========================+=====================+=============+====+
| CBOR Encoding | Diagnostic Notation | Description |Note|
+==========================+=====================+=============+====+
| a2616200616101 |{"b":0,"a":1} | Improper | 1 |
| | | map key | |
| | | ordering | |
+--------------------------+---------------------+-------------+----+
| 1900ff |255 | Number with | 1 |
| | | leading | |
| | | zero bytes | |
+--------------------------+---------------------+-------------+----+
| c34a00010000000000000000 |-18446744073709551617| Number with | 1 |
| | | leading | |
| | | zero bytes | |
+--------------------------+---------------------+-------------+----+
| Fa41280000 |10.5 | Not in | 1 |
| | | shortest | |
| | | encoding | |
+--------------------------+---------------------+-------------+----+
| fa7fc00000 |NaN | Not in | 1 |
| | | shortest | |
| | | encoding | |
+--------------------------+---------------------+-------------+----+
| c243010000 |65536 | Incorrect | 1 |
| | | value for | |
| | | bigint | |
+--------------------------+---------------------+-------------+----+
| f97e01 |NaN | NaN with | 1 |
| | | payload | |
+--------------------------+---------------------+-------------+----+
| f7 |undefined | Unsupported | |
| | | simple type | |
+--------------------------+---------------------+-------------+----+
| f0 |simple(16) | Unsupported | |
| | | simple type | |
+--------------------------+---------------------+-------------+----+
| 5f4101420203ff |(_ h'01', h'0203') | Unsupported | |
| | | indefinite | |
| | | length | |
| | | object | |
+--------------------------+---------------------+-------------+----+
Table 6: Invalid Encodings
1. See also Appendix C.
Rundgren Expires 19 September 2025 [Page 21]
Internet-Draft U-CBOR March 2025
Appendix B. Enveloped Signatures
This is a _non-normative_ appendix showing how U-CBOR can be used for
supporting enveloped signatures.
The primary advantages with _enveloped_ signatures compared to
_enveloping_ signatures (like used by COSE [RFC9052]), include:
* Keeping the _structure_ of the original (unsigned) data intact, by
simply making signatures an additional attribute.
* Enabling top-level, _object identifiers_ to become a part of the
signed data as well:
123456789({ # CBOR tag (objectId)
1: "This is not rocket science!", # Object instance data
2: [38.8882, -77.01988], # ""
3: «signature covering the entire object»
})
See also [COTX].
* Permitting signing CBOR data and associated security attributes
(aka "headers"), _in one go_, without having to wrap data in CBOR
"bstr" objects. Non-wrapped data also makes debugging and
documentation easier.
Enveloped signatures are for example featured in Verified Credentials
[CREDENTIALS]. A drawback with designs based on JSON [RFC8259] is
that they rely on _canonicalization schemes_ like JCS [RFC8785], that
require specialized encoders and decoders, whereas U-CBOR works
"straight out of the box".
B.1. Sample Signature
Although this specification is not "married" to any particular
signature schema, the following example uses the CBOR Signature
Format [CSF]. For the sake of simplicity, the example uses an HMAC
(see Appendix B.1.4) as signature algorithm.
For a more sophisticated use of U-CBOR, combining signatures and
encryption, see [WALLET].
B.1.1. Unsigned Data
Imagine you have a CBOR map object like the following that you want
to sign:
Rundgren Expires 19 September 2025 [Page 22]
Internet-Draft U-CBOR March 2025
{
1: "data",
2: "more data"
}
B.1.2. Signature Process
This section describes the steps required for adding an enveloped
signature to the CBOR map object in Appendix B.1.1. To avoid
confusing CBOR map keys with cryptographic keys, the former are
referred to as "labels".
1. Add an empty CSF container (a CBOR map) to the unsigned CBOR map
using an _application-defined_ label (-1).
2. Add the designated signature algorithm to the CSF container using
the CSF algorithm label (1).
3. _Optional_. Add other signature meta data to the CSF container.
Not used in the example.
4. Generate a signature by invoking a (hypothetical) signature
method with the following arguments:
* the designated signature key.
* the designated signature algorithm.
* the _deterministic encoding_ of the current CBOR object in its
_entirety_. In the example that would be
a301646461746102696d6f7265206461746120a10105, if expressed in
hex code.
5. Add the returned signature value to the CSF container using the
CSF signature label (6).
The result after the final step (using the parameters from
Appendix B.1.4), should match the following CBOR object:
{
1: "data",
2: "more data",
-1: {
1: 5,
6: h'4853d7730cc1340682b1748dc346cf627a5e91ce62c67fff15c40257ed2a37a1'
}
}
Rundgren Expires 19 September 2025 [Page 23]
Internet-Draft U-CBOR March 2025
Note that the signature covers the _entire_ CBOR object except for
the CSF signature value and label (6).
B.1.3. Validation Process
In order to validate the enveloped signature created in the
Appendix B.1.2, the following steps are performed:
1. Fetch a _reference_ to the CSF container using the _application-
defined_ label (-1). Next perform the following operations using
the reference:
1. Retrieve the signature algorithm using the CSF algorithm
label (1).
2. Retrieve the signature value using the CSF algorithm label
(6).
3. Remove the CSF algorithm label (6) and its associated value.
Now we should have exactly the same CBOR object as we had
_before_ step #4 in Appendix B.1.2. That is:
{
1: "data",
2: "more data",
-1: {
1: 5
}
}
2. Validate the signature data by invoking a (hypothetical)
signature validation method with the following arguments:
* the designated signature key (in the example taken from
Appendix B.1.4).
* the signature algorithm retrieved in step #1.
* the signature value retrieved in step #1.
* the _deterministic encoding_ of the current CBOR object in its
_entirety_.
Note: this is a "bare-bones" validation process, lacking the
ruggedness of a real-world implementation.
Rundgren Expires 19 September 2025 [Page 24]
Internet-Draft U-CBOR March 2025
B.1.4. Example Parameters
The signature and validation processes depend on the COSE [RFC9053]
algorithm "HMAC 256/256" and an associated 256-bit key, here provided
in hex code:
7fdd851a3b9d2dafc5f0d00030e22b9343900cd42ede4948568a4a2ee655291a
B.2. Code Example
Using a JavaScript implementation [CBOR.JS] of U-CBOR, together with
Node.js [NODE.JS], basic signature creation and validation supporting
the example in Appendix B.1, could be performed by the following
code:
// hmac.mjs
import CBOR from 'cbor-object';
const crypto = await import('node:crypto');
// CSF constants
const CSF_ALG_LBL = CBOR.Int(1);
const CSF_SIG_LBL = CBOR.Int(6);
// COSE => Node.js algorithm translation
const HASH_ALGORITHMS = new Map()
.set(5, "sha256").set(6, "sha384").set(7, "sha512");
function hmac(coseAlg, key, data) {
let alg = HASH_ALGORITHMS.get(coseAlg);
if (alg === undefined) throw "Unknown alg: " + coseAlg;
return crypto.createHmac(alg, key).update(data).digest();
}
const SHARED_KEY = crypto.createSecretKey(
'7fdd851a3b9d2dafc5f0d00030e22b9343900cd42ede4948568a4a2ee655291a', 'hex');
const APP_P1_LBL = CBOR.Int(1); // Application label
const APP_P2_LBL = CBOR.Int(2); // ""
const APP_CSF_LBL = CBOR.Int(-1); // Where to put the
// CSF container
////////////////////////////////////
// Create an unsigned CBOR object //
////////////////////////////////////
let object = CBOR.Map()
.set(APP_P1_LBL, CBOR.String("data")) // Application data
.set(APP_P2_LBL, CBOR.String("more data")); // ""
////////////////////////////////////////
Rundgren Expires 19 September 2025 [Page 25]
Internet-Draft U-CBOR March 2025
// Add a signature to the CBOR object //
////////////////////////////////////////
const COSE_ALG = 5; // Selected HMAC algorithm
let csf = CBOR.Map() // Create CSF container and
.set(CSF_ALG_LBL, CBOR.Int(COSE_ALG)); // add COSE algorithm to it
object.set(APP_CSF_LBL, csf); // Add CSF container to object
let sig = hmac(COSE_ALG, // Generate signature over
SHARED_KEY, // the current object
object.encode()); // encode(): all we got so far
csf.set(CSF_SIG_LBL, CBOR.Bytes(sig)); // Add signature to CSF container
let cborBinary = object.encode(); // Return CBOR as an Uint8Array
console.log(object.toString()); // Show in Diagnostic Notation
/////////////////////////////////////
// Validate the signed CBOR object //
/////////////////////////////////////
object = CBOR.decode(cborBinary); // Decode CBOR object
csf = object.get(APP_CSF_LBL); // Get CSF container
let alg = csf.get(CSF_ALG_LBL).getInt(); // Get COSE algorithm
let readSig = csf.remove(CSF_SIG_LBL).getBytes(); // Get and REMOVE signature value
let actualSig = hmac(alg, // Calculate signature over
SHARED_KEY, // the current object
object.encode()); // encode(): all but the signature
if (CBOR.compareArrays(readSig, actualSig)) { // HMAC validation
throw "Signature did not validate";
}
// Validated object, access the "payload":
let p1 = object.get(APP_P1_LBL).getString(); // p1 should now contain "data"
Note that this code depends heavily on the CBOR tool features
outlined in Section 2.3.
Appendix C. Supporting Existing Systems
It is assumed that _most_ systems using CBOR are able to process an
(_application specific_), selection of CBOR data items that are
encoded in compliance with [RFC8949]. Since the deterministic
encoding scheme mandated by U-CBOR, also is compliant with [RFC8949],
there should be no major interoperability issues. That is, if the
previous assumption actually is correct 😏
Rundgren Expires 19 September 2025 [Page 26]
Internet-Draft U-CBOR March 2025
However, in the _other_ direction (U-CBOR tools processing data from
Systems using "legacy" CBOR encoding schemes), the situation is
likely to be considerably more challenging since deterministic
encoding "by design" is _strict_. Due to this potential obstacle,
implementers of U-CBOR tools, are RECOMMENDED to offer _decoder_
options that permit "relaxing" the rigidness of deterministic
encoding with respect to:
Numbers:
Numbers MUST still be compliant with [RFC8949].
Sorted maps:
Duplicate keys MUST still be rejected.
Note that regardless of the format of decoded CBOR data, a compliant
U-CBOR implementation MUST maintain deterministic encoding. See also
Appendix A.3.
Appendix D. Compatible Online Tools
For testing and learning about U-CBOR, there are currently a number
of compatible online tools (subject to availability...).
[PLAYGROUND]:
Browser-based CBOR "playground"
[CSF-LAB]:
Server-based CBOR and [CSF] test system
Appendix E. Compatible Implementations
For using U-CBOR in applications, there are currently a number of
compatible libraries.
[CBOR.JS]:
JavaScript-based implementation supporting browsers as well as
[NODE.JS]
[OPENKEYSTORE]:
Java-based implementation that also supports [CSF] and [CEF]
[ANDROID-CBOR]:
Android Java-based implementation that also supports [CSF] and
[CEF]
Rundgren Expires 19 September 2025 [Page 27]
Internet-Draft U-CBOR March 2025
Document History
* 00. First cut.
* 01. Editorial. Changed order of columns in invalid encoding.
* 02. Editorial. "unwrapped" changed to "non-wrapped".
* 03:
Tweaking the abstract.
Protocol Primitives Support sub-section added.
Diagnostic Notation Support sub-section added.
Updated CBOR Tool Requirements
Updated code example to actually use crypto
Updated Acknowledgements.
Updated Security Considerations.
* 04:
Minor addition in CBOR tools
Updated Acknowledgements
* 05:
Regression bug fix
* 06:
Media type added
Acknowledgements
For verifying the correctness of the encoding scheme, the [CBOR.ME]
on-line CBOR tool, by the [RFC8949] author, Carsten Bormann, proved
to be invaluable.
Author's Address
Rundgren Expires 19 September 2025 [Page 28]
Internet-Draft U-CBOR March 2025
Anders Rundgren (editor)
Independent
Montpellier
France
Email: anders.rundgren.net@gmail.com
URI: https://www.linkedin.com/in/andersrundgren/
Rundgren Expires 19 September 2025 [Page 29]