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Montpellier France anders.rundgren.net@gmail.com https://www.linkedin.com/in/andersrundgren/

Application CBOR CBOR Encoding Deterministic This document describes a deterministic encoding scheme for CBOR intended for usage in high-end computing platforms like mobile phones, Web browsers, and Web servers. In addition to enhancing interoperability, deterministic encoding can also support cryptographic operations like signing CBOR data items. Using this specification, the latter can achieved without wrapping CBOR data items in byte strings or depend on canonicalization procedures.

Introduction This specification introduces a deterministic encoding scheme for data expressed in the CBOR format. This scheme is subsequently referred to as D&nbhy;CBOR.

Objectives The primary objective of D&nbhy;CBOR is providing an interoperable CBOR profile for high-end computing platforms like mobile phones, Web browsers, and Web servers. However, D&nbhy;CBOR also enables performing digital signatures over "raw" (unwrapped) CBOR data items since signatures depend on a unified representation of the data to be signed. In addition, D&nbhy;CBOR permits decoded CBOR data to be subjected to secure transformation and reencoding operations. The deterministic encoding scheme described in this document is characterized by being bidirectional also when CBOR is provided in diagnostic notation (Section 8 of ), making D&nbhy;CBOR comparatively easy to understand, debug, and implement. See also which represents an alternative approach to deterministic encoding.

Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", " SHALL NOT ", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Specification The deterministic encoding scheme used by D&nbhy;CBOR builds on Section 4.2 of . However, to achieve a fixed number representation as outlined in , Rule 2 in Section 4.2.2 MUST also be adhered to. A compliant D&nbhy;CBOR implementation SHOULD support the following CBOR data types:

• integer
• bignum
• floating point
• byte string
• text string
• true
• false
• null
• array
• map
• tag

See also .

IANA Considerations This document has no IANA actions.

Security Considerations This specification inherits all the security considerations of CBOR . Applications that exploit the uniqueness of deterministic encoding should verify that the used decoder actually flags incorrectly formatted CBOR data items.

References Normative References Informative References Blockchain Commons Blockchain Commons

Encoding of Numbers This section is normative. The following sub sections hold examples of numbers and their encoding using D&nbhy;CBOR. Note that the values and encodings are supposed to work in both directions.

Integer Numbers The following table holds a set of integers highlighting the selection between integer and bignum types. Integer Numbers

Value	Encoding
0	00
-1	20
23	17
24	1818
-24	37
-25	3818
255	18ff
256	190100
-256	38ff
-257	390100
65535	19ffff
65536	1a00010000
1099511627775	1b000000ffffffffff
18446744073709551615	1bffffffffffffffff
18446744073709551616	c249010000000000000000
-18446744073709551616	3bffffffffffffffff
-18446744073709551617	c349010000000000000000

Floating Point Numbers

Dedicated Floating Point Numbers The following table holds the set of dedicated IEEE 754 values. Note that NaN "signaling" MUST be flagged as an error. Dedicated Floating Point Numbers

Value	Encoding
0.0	f90000
-0.0	f98000
Infinity	f97c00
-Infinity	f9fc00
NaN	f97e00

Assorted Floating Point Numbers The following table holds a set of "ordinary" IEEE 754 values including some edge cases. Note that subnormal floating point values MUST be supported. Assorted Floating Point Numbers

Value	Encoding
-5.960464477539062e-8	fbbe6fffffffffffff
-5.9604644775390625e-8	f98001
-5.960464477539064e-8	fbbe70000000000001
-5.960465188081798e-8	fab3800001
0.00006097555160522461	f903ff
65504.0	f97bff
65504.00390625	fa477fe001
65536.0	fa47800000
10.559998512268066	fa4128f5c1
10.559998512268068	fb40251eb820000001
3.4028234663852886e+38	fa7f7fffff
3.402823466385289e+38	fb47efffffe0000001
1.401298464324817e-45	fa00000001
1.1754942106924411e-38	fa007fffff
5.0e-324	fb0000000000000001
-1.7976931348623157e+308	fbffefffffffffffff

Implementation Constraints This section is informative. Note that even if an application does not support (or need) bignum or floating point types, you can still use D-CBOR since a strict subset is upwardly compatible with full-blown implementations. Low-end platforms typically also restrict CBOR map keys to integer and text string types. Since these issues are application specific, they are out of scope for this specification.

Reference Implementations This section is informative. Reference implementations that conform to this specification include:

• JavaScript:
• JDK 17+:
• Android/Java:

Online Tools This section is informative. The following online tools enable testing D&nbhy;CBOR without installing any software:

Acknowledgements TBD

Document History [[ This section to be removed by the RFC Editor before publication as an RFC ]] Version 00:

• Initial publication.