draft-ietf-cbor-7049bis-03.txt   draft-ietf-cbor-7049bis-04.txt 
Network Working Group C. Bormann Network Working Group C. Bormann
Internet-Draft Universitaet Bremen TZI Internet-Draft Universitaet Bremen TZI
Intended status: Standards Track P. Hoffman Intended status: Standards Track P. Hoffman
Expires: March 24, 2019 ICANN Expires: April 26, 2019 ICANN
September 20, 2018 October 23, 2018
Concise Binary Object Representation (CBOR) Concise Binary Object Representation (CBOR)
draft-ietf-cbor-7049bis-03 draft-ietf-cbor-7049bis-04
Abstract Abstract
The Concise Binary Object Representation (CBOR) is a data format The Concise Binary Object Representation (CBOR) is a data format
whose design goals include the possibility of extremely small code whose design goals include the possibility of extremely small code
size, fairly small message size, and extensibility without the need size, fairly small message size, and extensibility without the need
for version negotiation. These design goals make it different from for version negotiation. These design goals make it different from
earlier binary serializations such as ASN.1 and MessagePack. earlier binary serializations such as ASN.1 and MessagePack.
Contributing Contributing
skipping to change at page 1, line 47 skipping to change at page 1, line 47
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 24, 2019. This Internet-Draft will expire on April 26, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 25 skipping to change at page 2, line 25
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Objectives . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Objectives . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. CBOR Data Models . . . . . . . . . . . . . . . . . . . . . . 6 2. CBOR Data Models . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Extended Generic Data Models . . . . . . . . . . . . . . 7 2.1. Extended Generic Data Models . . . . . . . . . . . . . . 8
2.2. Specific Data Models . . . . . . . . . . . . . . . . . . 8 2.2. Specific Data Models . . . . . . . . . . . . . . . . . . 8
3. Specification of the CBOR Encoding . . . . . . . . . . . . . 8 3. Specification of the CBOR Encoding . . . . . . . . . . . . . 9
3.1. Major Types . . . . . . . . . . . . . . . . . . . . . . . 9 3.1. Major Types . . . . . . . . . . . . . . . . . . . . . . . 10
3.2. Indefinite Lengths for Some Major Types . . . . . . . . . 11 3.2. Indefinite Lengths for Some Major Types . . . . . . . . . 11
3.2.1. Indefinite-Length Arrays and Maps . . . . . . . . . . 11 3.2.1. Indefinite-Length Arrays and Maps . . . . . . . . . . 12
3.2.2. Indefinite-Length Byte Strings and Text Strings . . . 13 3.2.2. Indefinite-Length Byte Strings and Text Strings . . . 14
3.3. Floating-Point Numbers and Values with No Content . . . . 14 3.3. Floating-Point Numbers and Values with No Content . . . . 15
3.4. Optional Tagging of Items . . . . . . . . . . . . . . . . 16 3.4. Optional Tagging of Items . . . . . . . . . . . . . . . . 16
3.4.1. Date and Time . . . . . . . . . . . . . . . . . . . . 18 3.4.1. Date and Time . . . . . . . . . . . . . . . . . . . . 18
3.4.2. Bignums . . . . . . . . . . . . . . . . . . . . . . . 18 3.4.2. Standard Date/Time String . . . . . . . . . . . . . . 18
3.4.3. Decimal Fractions and Bigfloats . . . . . . . . . . . 19 3.4.3. Epoch-based Date/Time . . . . . . . . . . . . . . . . 18
3.4.4. Content Hints . . . . . . . . . . . . . . . . . . . . 20 3.4.4. Bignums . . . . . . . . . . . . . . . . . . . . . . . 19
3.4.4.1. Encoded CBOR Data Item . . . . . . . . . . . . . 20 3.4.5. Decimal Fractions and Bigfloats . . . . . . . . . . . 20
3.4.4.2. Expected Later Encoding for CBOR-to-JSON 3.4.6. Content Hints . . . . . . . . . . . . . . . . . . . . 21
Converters . . . . . . . . . . . . . . . . . . . 20 3.4.6.1. Encoded CBOR Data Item . . . . . . . . . . . . . 21
3.4.4.3. Encoded Text . . . . . . . . . . . . . . . . . . 21 3.4.6.2. Expected Later Encoding for CBOR-to-JSON
3.4.5. Self-Describe CBOR . . . . . . . . . . . . . . . . . 21 Converters . . . . . . . . . . . . . . . . . . . 21
4. Creating CBOR-Based Protocols . . . . . . . . . . . . . . . . 22 3.4.6.3. Encoded Text . . . . . . . . . . . . . . . . . . 22
4.1. CBOR in Streaming Applications . . . . . . . . . . . . . 23 3.4.7. Self-Describe CBOR . . . . . . . . . . . . . . . . . 22
4.2. Generic Encoders and Decoders . . . . . . . . . . . . . . 23 4. Creating CBOR-Based Protocols . . . . . . . . . . . . . . . . 23
4.3. Syntax Errors . . . . . . . . . . . . . . . . . . . . . . 24 4.1. CBOR in Streaming Applications . . . . . . . . . . . . . 24
4.3.1. Incomplete CBOR Data Items . . . . . . . . . . . . . 24 4.2. Generic Encoders and Decoders . . . . . . . . . . . . . . 24
4.3.2. Malformed Indefinite-Length Items . . . . . . . . . . 24 4.3. Syntax Errors . . . . . . . . . . . . . . . . . . . . . . 25
4.3.3. Unknown Additional Information Values . . . . . . . . 25 4.3.1. Incomplete CBOR Data Items . . . . . . . . . . . . . 25
4.4. Other Decoding Errors . . . . . . . . . . . . . . . . . . 25 4.3.2. Malformed Indefinite-Length Items . . . . . . . . . . 25
4.5. Handling Unknown Simple Values and Tags . . . . . . . . . 26 4.3.3. Unknown Additional Information Values . . . . . . . . 26
4.6. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.7. Specifying Keys for Maps . . . . . . . . . . . . . . . . 27 4.4. Other Decoding Errors . . . . . . . . . . . . . . . . . . 26
4.7.1. Equivalence of Keys . . . . . . . . . . . . . . . . . 28 4.5. Handling Unknown Simple Values and Tags . . . . . . . . . 27
4.8. Undefined Values . . . . . . . . . . . . . . . . . . . . 29 4.6. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.9. Canonical CBOR . . . . . . . . . . . . . . . . . . . . . 29 4.7. Specifying Keys for Maps . . . . . . . . . . . . . . . . 28
4.9.1. Length-first map key ordering . . . . . . . . . . . . 31 4.7.1. Equivalence of Keys . . . . . . . . . . . . . . . . . 29
4.10. Strict Mode . . . . . . . . . . . . . . . . . . . . . . . 32 4.8. Undefined Values . . . . . . . . . . . . . . . . . . . . 30
5. Converting Data between CBOR and JSON . . . . . . . . . . . . 33 4.9. Preferred Serialization . . . . . . . . . . . . . . . . . 30
5.1. Converting from CBOR to JSON . . . . . . . . . . . . . . 33 4.10. Canonical CBOR . . . . . . . . . . . . . . . . . . . . . 31
5.2. Converting from JSON to CBOR . . . . . . . . . . . . . . 35 4.10.1. Length-first map key ordering . . . . . . . . . . . 33
6. Future Evolution of CBOR . . . . . . . . . . . . . . . . . . 36 4.11. Strict Mode . . . . . . . . . . . . . . . . . . . . . . . 34
6.1. Extension Points . . . . . . . . . . . . . . . . . . . . 36 5. Converting Data between CBOR and JSON . . . . . . . . . . . . 35
6.2. Curating the Additional Information Space . . . . . . . . 37 5.1. Converting from CBOR to JSON . . . . . . . . . . . . . . 35
7. Diagnostic Notation . . . . . . . . . . . . . . . . . . . . . 37 5.2. Converting from JSON to CBOR . . . . . . . . . . . . . . 37
7.1. Encoding Indicators . . . . . . . . . . . . . . . . . . . 38 6. Future Evolution of CBOR . . . . . . . . . . . . . . . . . . 37
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39 6.1. Extension Points . . . . . . . . . . . . . . . . . . . . 38
8.1. Simple Values Registry . . . . . . . . . . . . . . . . . 39 6.2. Curating the Additional Information Space . . . . . . . . 39
8.2. Tags Registry . . . . . . . . . . . . . . . . . . . . . . 39 7. Diagnostic Notation . . . . . . . . . . . . . . . . . . . . . 39
8.3. Media Type ("MIME Type") . . . . . . . . . . . . . . . . 40 7.1. Encoding Indicators . . . . . . . . . . . . . . . . . . . 40
8.4. CoAP Content-Format . . . . . . . . . . . . . . . . . . . 41 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 41
8.5. The +cbor Structured Syntax Suffix Registration . . . . . 41 8.1. Simple Values Registry . . . . . . . . . . . . . . . . . 41
9. Security Considerations . . . . . . . . . . . . . . . . . . . 42 8.2. Tags Registry . . . . . . . . . . . . . . . . . . . . . . 41
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 42 8.3. Media Type ("MIME Type") . . . . . . . . . . . . . . . . 42
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 43 8.4. CoAP Content-Format . . . . . . . . . . . . . . . . . . . 42
11.1. Normative References . . . . . . . . . . . . . . . . . . 43 8.5. The +cbor Structured Syntax Suffix Registration . . . . . 43
11.2. Informative References . . . . . . . . . . . . . . . . . 44 9. Security Considerations . . . . . . . . . . . . . . . . . . . 44
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 46 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 44
Appendix B. Jump Table . . . . . . . . . . . . . . . . . . . . . 50 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 45
Appendix C. Pseudocode . . . . . . . . . . . . . . . . . . . . . 53 11.1. Normative References . . . . . . . . . . . . . . . . . . 45
Appendix D. Half-Precision . . . . . . . . . . . . . . . . . . . 55 11.2. Informative References . . . . . . . . . . . . . . . . . 46
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 48
Appendix B. Jump Table . . . . . . . . . . . . . . . . . . . . . 52
Appendix C. Pseudocode . . . . . . . . . . . . . . . . . . . . . 55
Appendix D. Half-Precision . . . . . . . . . . . . . . . . . . . 57
Appendix E. Comparison of Other Binary Formats to CBOR's Design Appendix E. Comparison of Other Binary Formats to CBOR's Design
Objectives . . . . . . . . . . . . . . . . . . . . . 56 Objectives . . . . . . . . . . . . . . . . . . . . . 58
E.1. ASN.1 DER, BER, and PER . . . . . . . . . . . . . . . . . 57 E.1. ASN.1 DER, BER, and PER . . . . . . . . . . . . . . . . . 59
E.2. MessagePack . . . . . . . . . . . . . . . . . . . . . . . 57 E.2. MessagePack . . . . . . . . . . . . . . . . . . . . . . . 59
E.3. BSON . . . . . . . . . . . . . . . . . . . . . . . . . . 58 E.3. BSON . . . . . . . . . . . . . . . . . . . . . . . . . . 60
E.4. UBJSON . . . . . . . . . . . . . . . . . . . . . . . . . 58 E.4. MSDTP: RFC 713 . . . . . . . . . . . . . . . . . . . . . 60
E.5. MSDTP: RFC 713 . . . . . . . . . . . . . . . . . . . . . 58 E.5. Conciseness on the Wire . . . . . . . . . . . . . . . . . 60
E.6. Conciseness on the Wire . . . . . . . . . . . . . . . . . 58 Appendix F. Changes from RFC 7049 . . . . . . . . . . . . . . . 61
Appendix F. Changes from RFC 7049 . . . . . . . . . . . . . . . 59 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 61
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 59
1. Introduction 1. Introduction
There are hundreds of standardized formats for binary representation There are hundreds of standardized formats for binary representation
of structured data (also known as binary serialization formats). Of of structured data (also known as binary serialization formats). Of
those, some are for specific domains of information, while others are those, some are for specific domains of information, while others are
generalized for arbitrary data. In the IETF, probably the best-known generalized for arbitrary data. In the IETF, probably the best-known
formats in the latter category are ASN.1's BER and DER [ASN.1]. formats in the latter category are ASN.1's BER and DER [ASN.1].
The format defined here follows some specific design goals that are The format defined here follows some specific design goals that are
skipping to change at page 6, line 45 skipping to change at page 6, line 49
of the data items in the sequence available to an application as of the data items in the sequence available to an application as
they are received. they are received.
Where bit arithmetic or data types are explained, this document uses Where bit arithmetic or data types are explained, this document uses
the notation familiar from the programming language C, except that the notation familiar from the programming language C, except that
"**" denotes exponentiation. Similar to the "0x" notation for "**" denotes exponentiation. Similar to the "0x" notation for
hexadecimal numbers, numbers in binary notation are prefixed with hexadecimal numbers, numbers in binary notation are prefixed with
"0b". Underscores can be added to such a number solely for "0b". Underscores can be added to such a number solely for
readability, so 0b00100001 (0x21) might be written 0b001_00001 to readability, so 0b00100001 (0x21) might be written 0b001_00001 to
emphasize the desired interpretation of the bits in the byte; in this emphasize the desired interpretation of the bits in the byte; in this
case, it is split into three bits and five bits. case, it is split into three bits and five bits. Encoded CBOR data
items are sometimes given in the "0x" or "0b" notation; these values
are first interpreted as numbers as in C and are then interpreted as
byte strings in network byte order, including any leading zero bytes
expressed in the notation.
2. CBOR Data Models 2. CBOR Data Models
CBOR is explicit about its generic data model, which defines the set CBOR is explicit about its generic data model, which defines the set
of all data items that can be represented in CBOR. Its basic generic of all data items that can be represented in CBOR. Its basic generic
data model is extensible by the registration of simple type values data model is extensible by the registration of simple type values
and tags. Applications can then subset the resulting extended and tags. Applications can then subset the resulting extended
generic data model to build their specific data models. generic data model to build their specific data models.
Within environments that can represent the data items in the generic Within environments that can represent the data items in the generic
skipping to change at page 7, line 25 skipping to change at page 7, line 33
In the basic (un-extended) generic data model, a data item is one of: In the basic (un-extended) generic data model, a data item is one of:
o an integer in the range -2**64..2**64-1 inclusive o an integer in the range -2**64..2**64-1 inclusive
o a simple value, identified by a number between 0 and 255, but o a simple value, identified by a number between 0 and 255, but
distinct from that number distinct from that number
o a floating point value, distinct from an integer, out of the set o a floating point value, distinct from an integer, out of the set
representable by IEEE 754 binary64 (including non-finites) representable by IEEE 754 binary64 (including non-finites)
[IEEE.754.2008]
o a sequence of zero or more bytes ("byte string") o a sequence of zero or more bytes ("byte string")
o a sequence of zero or more Unicode code points ("text string") o a sequence of zero or more Unicode code points ("text string")
o a sequence of zero or more data items ("array") o a sequence of zero or more data items ("array")
o a mapping (mathematical function) from zero or more data items o a mapping (mathematical function) from zero or more data items
("keys") each to a data item ("values"), ("map") ("keys") each to a data item ("values"), ("map")
o a tagged data item, comprising a tag (an integer in the range o a tagged data item, comprising a tag (an integer in the range
0..2**64-1) and a value (a data item) 0..2**64-1) and a value (a data item)
Note that integer and floating-point values are distinct in this Note that integer and floating-point values are distinct in this
model, even if they have the same numeric value. model, even if they have the same numeric value.
Also note that serialization variants, such as number of bytes of the
encoded floating value, or the choice of one of the ways in which an
integer, the length of a text or byte string, the number of elements
in an array or pairs in a map, or a tag value, (collectively "the
argument", see Section 3) can be encoded, are not visible at the
generic data model level.
2.1. Extended Generic Data Models 2.1. Extended Generic Data Models
This basic generic data model comes pre-extended by the registration This basic generic data model comes pre-extended by the registration
of a number of simple values and tags right in this document, such of a number of simple values and tags right in this document, such
as: as:
o "false", "true", "null", and "undefined" (simple values identified o "false", "true", "null", and "undefined" (simple values identified
by 20..23) by 20..23)
o integer and floating point values with a larger range and o integer and floating point values with a larger range and
skipping to change at page 8, line 32 skipping to change at page 8, line 48
intentionally omitted) in the form appropriate for their programming intentionally omitted) in the form appropriate for their programming
environment, implementation of the data model extensions created by environment, implementation of the data model extensions created by
tags is truly optional and a matter of implementation quality. tags is truly optional and a matter of implementation quality.
2.2. Specific Data Models 2.2. Specific Data Models
The specific data model for a CBOR-based protocol usually subsets the The specific data model for a CBOR-based protocol usually subsets the
extended generic data model and assigns application semantics to the extended generic data model and assigns application semantics to the
data items within this subset and its components. When documenting data items within this subset and its components. When documenting
such specific data models, where it is desired to specify the types such specific data models, where it is desired to specify the types
of data items, it is preferred to identify the types by their names of data items, it is preferred to identify the types by the names
in the generic data model ("negative integer", "array") instead of by they have in the generic data model ("negative integer", "array")
referring to aspects of their CBOR representation ("major type 1", instead of by referring to aspects of their CBOR representation
"major type 4"). ("major type 1", "major type 4").
Specific data models can also specify that values of different types Specific data models can also specify what values (including values
are equivalent for the purposes of map keys and encoder freedom. For of different types) are equivalent for the purposes of map keys and
example, in the generic data model, a valid map MAY have both "0" and encoder freedom. For example, in the generic data model, a valid map
"0.0" as keys, and an encoder MUST NOT encode "0.0" as an integer MAY have both "0" and "0.0" as keys, and an encoder MUST NOT encode
(major type 0, Section 3.1). However, if a specific data model "0.0" as an integer (major type 0, Section 3.1). However, if a
declares that floating point and integer representations of integral specific data model declares that floating point and integer
values are equivalent, map keys "0" and "0.0" would be considered representations of integral values are equivalent, using both map
duplicates and so invalid, and an encoder could encode integral- keys "0" and "0.0" in a single map would be considered duplicates and
valued floats as integers or vice versa, perhaps to save encoded so invalid, and an encoder could encode integral-valued floats as
bytes. integers or vice versa, perhaps to save encoded bytes.
3. Specification of the CBOR Encoding 3. Specification of the CBOR Encoding
A CBOR data item (Section 2) is encoded to or decoded from a byte A CBOR data item (Section 2) is encoded to or decoded from a byte
string as described in this section. The encoding is summarized in string as described in this section. The encoding is summarized in
Table 5. Table 5.
The initial byte of each encoded data item contains both information The initial byte of each encoded data item contains both information
about the major type (the high-order 3 bits, described in about the major type (the high-order 3 bits, described in
Section 3.1) and additional information (the low-order 5 bits). Section 3.1) and additional information (the low-order 5 bits).
skipping to change at page 16, line 6 skipping to change at page 16, line 26
| 23 | Undefined value | | 23 | Undefined value |
| | | | | |
| 24..31 | (Reserved) | | 24..31 | (Reserved) |
| | | | | |
| 32..255 | (Unassigned) | | 32..255 | (Unassigned) |
+---------+-----------------+ +---------+-----------------+
Table 2: Simple Values Table 2: Simple Values
The 5-bit values of 25, 26, and 27 are for 16-bit, 32-bit, and 64-bit The 5-bit values of 25, 26, and 27 are for 16-bit, 32-bit, and 64-bit
IEEE 754 binary floating-point values. These floating-point values IEEE 754 binary floating-point values [IEEE.754.2008]. These
are encoded in the additional bytes of the appropriate size. (See floating-point values are encoded in the additional bytes of the
Appendix D for some information about 16-bit floating point.) appropriate size. (See Appendix D for some information about 16-bit
floating point.)
An encoder MUST NOT encode False as the two-byte sequence of 0xf814, An encoder MUST NOT encode False as the two-byte sequence of 0xf814,
MUST NOT encode True as the two-byte sequence of 0xf815, MUST NOT MUST NOT encode True as the two-byte sequence of 0xf815, MUST NOT
encode Null as the two-byte sequence of 0xf816, and MUST NOT encode encode Null as the two-byte sequence of 0xf816, and MUST NOT encode
Undefined value as the two-byte sequence of 0xf817. A decoder MUST Undefined value as the two-byte sequence of 0xf817. A decoder MUST
treat these two-byte sequences as an error. Similar prohibitions treat these two-byte sequences as an error. Similar prohibitions
apply to the unassigned simple values as well. apply to the unassigned simple values as well.
3.4. Optional Tagging of Items 3.4. Optional Tagging of Items
skipping to change at page 16, line 30 skipping to change at page 16, line 51
additional semantics while retaining its structure. The tag is major additional semantics while retaining its structure. The tag is major
type 6, and represents an integer number as indicated by the tag's type 6, and represents an integer number as indicated by the tag's
argument (Section 3); the (sole) data item is carried as content argument (Section 3); the (sole) data item is carried as content
data. If a tag requires structured data, this structure is encoded data. If a tag requires structured data, this structure is encoded
into the nested data item. The definition of a tag usually restricts into the nested data item. The definition of a tag usually restricts
what kinds of nested data item or items are valid. what kinds of nested data item or items are valid.
The initial bytes of the tag follow the rules for positive integers The initial bytes of the tag follow the rules for positive integers
(major type 0). The tag is followed by a single data item of any (major type 0). The tag is followed by a single data item of any
type. For example, assume that a byte string of length 12 is marked type. For example, assume that a byte string of length 12 is marked
with a tag to indicate it is a positive bignum (Section 3.4.2). This with a tag to indicate it is a positive bignum (Section 3.4.4). This
would be marked as 0b110_00010 (major type 6, additional information would be marked as 0b110_00010 (major type 6, additional information
2 for the tag) followed by 0b010_01100 (major type 2, additional 2 for the tag) followed by 0b010_01100 (major type 2, additional
information of 12 for the length) followed by the 12 bytes of the information of 12 for the length) followed by the 12 bytes of the
bignum. bignum.
Decoders do not need to understand tags, and thus tags may be of Decoders do not need to understand tags, and thus tags may be of
little value in applications where the implementation creating a little value in applications where the implementation creating a
particular CBOR data item and the implementation decoding that stream particular CBOR data item and the implementation decoding that stream
know the semantic meaning of each item in the data flow. Their know the semantic meaning of each item in the data flow. Their
primary purpose in this specification is to define common data types primary purpose in this specification is to define common data types
skipping to change at page 17, line 12 skipping to change at page 17, line 33
value. The content of the tagged item is the data item (the value) value. The content of the tagged item is the data item (the value)
that is being tagged. that is being tagged.
IANA maintains a registry of tag values as described in Section 8.2. IANA maintains a registry of tag values as described in Section 8.2.
Table 3 provides a list of initial values, with definitions in the Table 3 provides a list of initial values, with definitions in the
rest of this section. rest of this section.
+-----------+--------------+----------------------------------------+ +-----------+--------------+----------------------------------------+
| Tag | Data Item | Semantics | | Tag | Data Item | Semantics |
+-----------+--------------+----------------------------------------+ +-----------+--------------+----------------------------------------+
| 0 | UTF-8 string | Standard date/time string; see | | 0 | UTF-8 string | Standard date/time string; see Section |
| | | Section 3.4.1 | | | | 3.4.2 |
| | | | | | | |
| 1 | multiple | Epoch-based date/time; see | | 1 | multiple | Epoch-based date/time; see Section |
| | | Section 3.4.1 | | | | 3.4.3 |
| | | | | | | |
| 2 | byte string | Positive bignum; see Section 3.4.2 | | 2 | byte string | Positive bignum; see Section 3.4.4 |
| | | | | | | |
| 3 | byte string | Negative bignum; see Section 3.4.2 | | 3 | byte string | Negative bignum; see Section 3.4.4 |
| | | | | | | |
| 4 | array | Decimal fraction; see Section 3.4.3 | | 4 | array | Decimal fraction; see Section 3.4.5 |
| | | | | | | |
| 5 | array | Bigfloat; see Section 3.4.3 | | 5 | array | Bigfloat; see Section 3.4.5 |
| | | | | | | |
| 6..20 | (Unassigned) | (Unassigned) | | 6..20 | (Unassigned) | (Unassigned) |
| | | | | | | |
| 21 | multiple | Expected conversion to base64url | | 21 | multiple | Expected conversion to base64url |
| | | encoding; see Section 3.4.4.2 | | | | encoding; see Section 3.4.6.2 |
| | | | | | | |
| 22 | multiple | Expected conversion to base64 | | 22 | multiple | Expected conversion to base64 |
| | | encoding; see Section 3.4.4.2 | | | | encoding; see Section 3.4.6.2 |
| | | | | | | |
| 23 | multiple | Expected conversion to base16 | | 23 | multiple | Expected conversion to base16 |
| | | encoding; see Section 3.4.4.2 | | | | encoding; see Section 3.4.6.2 |
| | | | | | | |
| 24 | byte string | Encoded CBOR data item; see | | 24 | byte string | Encoded CBOR data item; see Section |
| | | Section 3.4.4.1 | | | | 3.4.6.1 |
| | | | | | | |
| 25..31 | (Unassigned) | (Unassigned) | | 25..31 | (Unassigned) | (Unassigned) |
| | | | | | | |
| 32 | UTF-8 string | URI; see Section 3.4.4.3 | | 32 | UTF-8 string | URI; see Section 3.4.6.3 |
| | | | | | | |
| 33 | UTF-8 string | base64url; see Section 3.4.4.3 | | 33 | UTF-8 string | base64url; see Section 3.4.6.3 |
| | | | | | | |
| 34 | UTF-8 string | base64; see Section 3.4.4.3 | | 34 | UTF-8 string | base64; see Section 3.4.6.3 |
| | | | | | | |
| 35 | UTF-8 string | Regular expression; see | | 35 | UTF-8 string | Regular expression; see Section |
| | | Section 3.4.4.3 | | | | 3.4.6.3 |
| | | | | | | |
| 36 | UTF-8 string | MIME message; see Section 3.4.4.3 | | 36 | UTF-8 string | MIME message; see Section 3.4.6.3 |
| | | | | | | |
| 37..55798 | (Unassigned) | (Unassigned) | | 37..55798 | (Unassigned) | (Unassigned) |
| | | | | | | |
| 55799 | multiple | Self-describe CBOR; see Section 3.4.5 | | 55799 | multiple | Self-describe CBOR; see Section 3.4.7 |
| | | | | | | |
| 55800+ | (Unassigned) | (Unassigned) | | 55800+ | (Unassigned) | (Unassigned) |
+-----------+--------------+----------------------------------------+ +-----------+--------------+----------------------------------------+
Table 3: Values for Tags Table 3: Values for Tags
3.4.1. Date and Time 3.4.1. Date and Time
Protocols using tag values 0 and 1 extend the generic data model Protocols using tag values 0 and 1 extend the generic data model
(Section 2) with data items representing points in time. (Section 2) with data items representing points in time.
3.4.2. Standard Date/Time String
Tag value 0 is for date/time strings that follow the standard format Tag value 0 is for date/time strings that follow the standard format
described in [RFC3339], as refined by Section 3.3 of [RFC4287]. described in [RFC3339], as refined by Section 3.3 of [RFC4287].
Tag value 1 is for numerical representation of seconds relative to 3.4.3. Epoch-based Date/Time
1970-01-01T00:00Z in UTC time. (For the non-negative values that the
Portable Operating System Interface (POSIX) defines, the number of
seconds is counted in the same way as for POSIX "seconds since the
epoch" [TIME_T].) The tagged item can be a positive or negative
integer (major types 0 and 1), or a floating-point number (major type
7 with additional information 25, 26, or 27). Note that the number
can be negative (time before 1970-01-01T00:00Z) and, if a floating-
point number, indicate fractional seconds.
3.4.2. Bignums Tag value 1 is for numerical representation of civil time expressed
in seconds relative to 1970-01-01T00:00Z (in UTC time).
The tagged item MUST be an unsigned or negative integer (major types
0 and 1), or a floating-point number (major type 7 with additional
information 25, 26, or 27).
Non-negative values (major type 0 and non-negative floating-point
numbers) stand for time values on or after 1970-01-01T00:00Z UTC and
are interpreted according to POSIX [TIME_T]. (POSIX time is also
known as UNIX Epoch time. Note that leap seconds are handled
specially by POSIX time and this results in a 1 second discontinuity
several times per decade.) Note that applications that require the
expression of times beyond early 2106 cannot leave out support of
64-bit integers for the tagged value.
Negative values (major type 1 and negative floating-point numbers)
are interpreted as determined by the application requirements as
there is no universal standard for UTC count-of-seconds time before
1970-01-01T00:00Z (this is particularly true for points in time that
precede discontinuities in national calendars).
To indicate fractional seconds, floating point values can be used
within Tag 1 instead of integer values. Note that this generally
requires binary64 support, as binary16 and binary32 provide non-zero
fractions of seconds only for a short period of time around early
1970. An application that requires Tag 1 support may restrict the
tagged value to be an integer (or a floating-point value) only.
3.4.4. Bignums
Protocols using tag values 2 and 3 extend the generic data model Protocols using tag values 2 and 3 extend the generic data model
(Section 2) with "bignums" representing arbitrary integers. In the (Section 2) with "bignums" representing arbitrary integers. In the
generic data model, bignum values are not equal to integers from the generic data model, bignum values are not equal to integers from the
basic data model, but specific data models can define that basic data model, but specific data models can define that
equivalence. equivalence.
Bignums are encoded as a byte string data item, which is interpreted Bignums are encoded as a byte string data item, which is interpreted
as an unsigned integer n in network byte order. For tag value 2, the as an unsigned integer n in network byte order. For tag value 2, the
value of the bignum is n. For tag value 3, the value of the bignum value of the bignum is n. For tag value 3, the value of the bignum
skipping to change at page 19, line 9 skipping to change at page 20, line 5
For example, the number 18446744073709551616 (2**64) is represented For example, the number 18446744073709551616 (2**64) is represented
as 0b110_00010 (major type 6, tag 2), followed by 0b010_01001 (major as 0b110_00010 (major type 6, tag 2), followed by 0b010_01001 (major
type 2, length 9), followed by 0x010000000000000000 (one byte 0x01 type 2, length 9), followed by 0x010000000000000000 (one byte 0x01
and eight bytes 0x00). In hexadecimal: and eight bytes 0x00). In hexadecimal:
C2 -- Tag 2 C2 -- Tag 2
49 -- Byte string of length 9 49 -- Byte string of length 9
010000000000000000 -- Bytes content 010000000000000000 -- Bytes content
3.4.3. Decimal Fractions and Bigfloats 3.4.5. Decimal Fractions and Bigfloats
Protocols using tag value 4 extend the generic data model with data Protocols using tag value 4 extend the generic data model with data
items representing arbitrary-length decimal fractions m*(10*e). items representing arbitrary-length decimal fractions m*(10*e).
Protocols using tag value 5 extend the generic data model with data Protocols using tag value 5 extend the generic data model with data
items representing arbitrary-length binary fractions m*(2*e). As items representing arbitrary-length binary fractions m*(2*e). As
with bignums, values of different types are not equal in the generic with bignums, values of different types are not equal in the generic
data model. data model.
Decimal fractions combine an integer mantissa with a base-10 scaling Decimal fractions combine an integer mantissa with a base-10 scaling
factor. They are most useful if an application needs the exact factor. They are most useful if an application needs the exact
skipping to change at page 19, line 37 skipping to change at page 20, line 33
(Section 3.3). Bigfloats may also be used by constrained (Section 3.3). Bigfloats may also be used by constrained
applications that need some basic binary floating-point capability applications that need some basic binary floating-point capability
without the need for supporting IEEE 754. without the need for supporting IEEE 754.
A decimal fraction or a bigfloat is represented as a tagged array A decimal fraction or a bigfloat is represented as a tagged array
that contains exactly two integer numbers: an exponent e and a that contains exactly two integer numbers: an exponent e and a
mantissa m. Decimal fractions (tag 4) use base-10 exponents; the mantissa m. Decimal fractions (tag 4) use base-10 exponents; the
value of a decimal fraction data item is m*(10**e). Bigfloats (tag value of a decimal fraction data item is m*(10**e). Bigfloats (tag
5) use base-2 exponents; the value of a bigfloat data item is 5) use base-2 exponents; the value of a bigfloat data item is
m*(2**e). The exponent e MUST be represented in an integer of major m*(2**e). The exponent e MUST be represented in an integer of major
type 0 or 1, while the mantissa also can be a bignum (Section 3.4.2). type 0 or 1, while the mantissa also can be a bignum (Section 3.4.4).
An example of a decimal fraction is that the number 273.15 could be An example of a decimal fraction is that the number 273.15 could be
represented as 0b110_00100 (major type of 6 for the tag, additional represented as 0b110_00100 (major type of 6 for the tag, additional
information of 4 for the type of tag), followed by 0b100_00010 (major information of 4 for the type of tag), followed by 0b100_00010 (major
type of 4 for the array, additional information of 2 for the length type of 4 for the array, additional information of 2 for the length
of the array), followed by 0b001_00001 (major type of 1 for the first of the array), followed by 0b001_00001 (major type of 1 for the first
integer, additional information of 1 for the value of -2), followed integer, additional information of 1 for the value of -2), followed
by 0b000_11001 (major type of 0 for the second integer, additional by 0b000_11001 (major type of 0 for the second integer, additional
information of 25 for a two-byte value), followed by information of 25 for a two-byte value), followed by
0b0110101010110011 (27315 in two bytes). In hexadecimal: 0b0110101010110011 (27315 in two bytes). In hexadecimal:
skipping to change at page 20, line 29 skipping to change at page 21, line 25
Decimal fractions and bigfloats provide no representation of Decimal fractions and bigfloats provide no representation of
Infinity, -Infinity, or NaN; if these are needed in place of a Infinity, -Infinity, or NaN; if these are needed in place of a
decimal fraction or bigfloat, the IEEE 754 half-precision decimal fraction or bigfloat, the IEEE 754 half-precision
representations from Section 3.3 can be used. For constrained representations from Section 3.3 can be used. For constrained
applications, where there is a choice between representing a specific applications, where there is a choice between representing a specific
number as an integer and as a decimal fraction or bigfloat (such as number as an integer and as a decimal fraction or bigfloat (such as
when the exponent is small and non-negative), there is a quality-of- when the exponent is small and non-negative), there is a quality-of-
implementation expectation that the integer representation is used implementation expectation that the integer representation is used
directly. directly.
3.4.4. Content Hints 3.4.6. Content Hints
The tags in this section are for content hints that might be used by The tags in this section are for content hints that might be used by
generic CBOR processors. These content hints do not extend the generic CBOR processors. These content hints do not extend the
generic data model. generic data model.
3.4.4.1. Encoded CBOR Data Item 3.4.6.1. Encoded CBOR Data Item
Sometimes it is beneficial to carry an embedded CBOR data item that Sometimes it is beneficial to carry an embedded CBOR data item that
is not meant to be decoded immediately at the time the enclosing data is not meant to be decoded immediately at the time the enclosing data
item is being parsed. Tag 24 (CBOR data item) can be used to tag the item is being parsed. Tag 24 (CBOR data item) can be used to tag the
embedded byte string as a data item encoded in CBOR format. embedded byte string as a data item encoded in CBOR format.
3.4.4.2. Expected Later Encoding for CBOR-to-JSON Converters 3.4.6.2. Expected Later Encoding for CBOR-to-JSON Converters
Tags 21 to 23 indicate that a byte string might require a specific Tags 21 to 23 indicate that a byte string might require a specific
encoding when interoperating with a text-based representation. These encoding when interoperating with a text-based representation. These
tags are useful when an encoder knows that the byte string data it is tags are useful when an encoder knows that the byte string data it is
writing is likely to be later converted to a particular JSON-based writing is likely to be later converted to a particular JSON-based
usage. That usage specifies that some strings are encoded as base64, usage. That usage specifies that some strings are encoded as base64,
base64url, and so on. The encoder uses byte strings instead of doing base64url, and so on. The encoder uses byte strings instead of doing
the encoding itself to reduce the message size, to reduce the code the encoding itself to reduce the message size, to reduce the code
size of the encoder, or both. The encoder does not know whether or size of the encoder, or both. The encoder does not know whether or
not the converter will be generic, and therefore wants to say what it not the converter will be generic, and therefore wants to say what it
skipping to change at page 21, line 19 skipping to change at page 22, line 17
contained in the data item, except for those contained in a nested contained in the data item, except for those contained in a nested
data item tagged with an expected conversion. data item tagged with an expected conversion.
These three tag types suggest conversions to three of the base data These three tag types suggest conversions to three of the base data
encodings defined in [RFC4648]. For base64url encoding, padding is encodings defined in [RFC4648]. For base64url encoding, padding is
not used (see Section 3.2 of RFC 4648); that is, all trailing equals not used (see Section 3.2 of RFC 4648); that is, all trailing equals
signs ("=") are removed from the base64url-encoded string. Later signs ("=") are removed from the base64url-encoded string. Later
tags might be defined for other data encodings of RFC 4648 or for tags might be defined for other data encodings of RFC 4648 or for
other ways to encode binary data in strings. other ways to encode binary data in strings.
3.4.4.3. Encoded Text 3.4.6.3. Encoded Text
Some text strings hold data that have formats widely used on the Some text strings hold data that have formats widely used on the
Internet, and sometimes those formats can be validated and presented Internet, and sometimes those formats can be validated and presented
to the application in appropriate form by the decoder. There are to the application in appropriate form by the decoder. There are
tags for some of these formats. tags for some of these formats.
o Tag 32 is for URIs, as defined in [RFC3986]; o Tag 32 is for URIs, as defined in [RFC3986];
o Tags 33 and 34 are for base64url- and base64-encoded text strings, o Tags 33 and 34 are for base64url- and base64-encoded text strings,
as defined in [RFC4648]; as defined in [RFC4648];
skipping to change at page 21, line 46 skipping to change at page 22, line 44
expression, or more than just the text of the regular expression expression, or more than just the text of the regular expression
itself, need to be conveyed.) itself, need to be conveyed.)
o Tag 36 is for MIME messages (including all headers), as defined in o Tag 36 is for MIME messages (including all headers), as defined in
[RFC2045]; [RFC2045];
Note that tags 33 and 34 differ from 21 and 22 in that the data is Note that tags 33 and 34 differ from 21 and 22 in that the data is
transported in base-encoded form for the former and in raw byte transported in base-encoded form for the former and in raw byte
string form for the latter. string form for the latter.
3.4.5. Self-Describe CBOR 3.4.7. Self-Describe CBOR
In many applications, it will be clear from the context that CBOR is In many applications, it will be clear from the context that CBOR is
being employed for encoding a data item. For instance, a specific being employed for encoding a data item. For instance, a specific
protocol might specify the use of CBOR, or a media type is indicated protocol might specify the use of CBOR, or a media type is indicated
that specifies its use. However, there may be applications where that specifies its use. However, there may be applications where
such context information is not available, such as when CBOR data is such context information is not available, such as when CBOR data is
stored in a file and disambiguating metadata is not in use. Here, it stored in a file and disambiguating metadata is not in use. Here, it
may help to have some distinguishing characteristics for the data may help to have some distinguishing characteristics for the data
itself. itself.
skipping to change at page 27, line 12 skipping to change at page 28, line 12
specific integer encodings that are longer than necessary for the specific integer encodings that are longer than necessary for the
application, such as to save the need to implement 64-bit integers. application, such as to save the need to implement 64-bit integers.
There is an expectation that encoders will use the most compact There is an expectation that encoders will use the most compact
integer representation that can represent a given value. However, a integer representation that can represent a given value. However, a
compact application should accept values that use a longer-than- compact application should accept values that use a longer-than-
needed encoding (such as encoding "0" as 0b000_11001 followed by two needed encoding (such as encoding "0" as 0b000_11001 followed by two
bytes of 0x00) as long as the application can decode an integer of bytes of 0x00) as long as the application can decode an integer of
the given size. the given size.
The preferred encoding for a floating point value is the shortest
floating point encoding that preserves its value, e.g., 0xf94580 for
the number 5.5, and 0xfa45ad9c00 for the number 5555.5, unless the
CBOR-based protocol specifically excludes the use of the shorter
floating point encodings. For NaN values, a shorter encoding is
preferred if zero-padding the shorter significand towards the right
reconstitutes the original NaN value (for many applications, the
single NaN encoding 0xf97e00 will suffice).
4.7. Specifying Keys for Maps 4.7. Specifying Keys for Maps
The encoding and decoding applications need to agree on what types of The encoding and decoding applications need to agree on what types of
keys are going to be used in maps. In applications that need to keys are going to be used in maps. In applications that need to
interwork with JSON-based applications, keys probably should be interwork with JSON-based applications, keys probably should be
limited to UTF-8 strings only; otherwise, there has to be a specified limited to UTF-8 strings only; otherwise, there has to be a specified
mapping from the other CBOR types to Unicode characters, and this mapping from the other CBOR types to Unicode characters, and this
often leads to implementation errors. In applications where keys are often leads to implementation errors. In applications where keys are
numeric in nature and numeric ordering of keys is important to the numeric in nature and numeric ordering of keys is important to the
application, directly using the numbers for the keys is useful. application, directly using the numbers for the keys is useful.
skipping to change at page 27, line 47 skipping to change at page 29, line 7
source to maintain uniqueness. source to maintain uniqueness.
A CBOR-based protocol should make an intentional decision about what A CBOR-based protocol should make an intentional decision about what
to do when a receiving application does see multiple identical keys to do when a receiving application does see multiple identical keys
in a map. The resulting rule in the protocol should respect the CBOR in a map. The resulting rule in the protocol should respect the CBOR
data model: it cannot prescribe a specific handling of the entries data model: it cannot prescribe a specific handling of the entries
with the identical keys, except that it might have a rule that having with the identical keys, except that it might have a rule that having
identical keys in a map indicates a malformed map and that the identical keys in a map indicates a malformed map and that the
decoder has to stop with an error. Duplicate keys are also decoder has to stop with an error. Duplicate keys are also
prohibited by CBOR decoders that are using strict mode prohibited by CBOR decoders that are using strict mode
(Section 4.10). (Section 4.11).
The CBOR data model for maps does not allow ascribing semantics to The CBOR data model for maps does not allow ascribing semantics to
the order of the key/value pairs in the map representation. Thus, a the order of the key/value pairs in the map representation. Thus, a
CBOR-based protocol MUST NOT specify that changing the key/value pair CBOR-based protocol MUST NOT specify that changing the key/value pair
order in a map would change the semantics, except to specify that order in a map would change the semantics, except to specify that
some, e.g. non-canonical, orders are disallowed. Timing, cache some, e.g. non-canonical, orders are disallowed. Timing, cache
usage, and other side channels are not considered part of the usage, and other side channels are not considered part of the
semantics. semantics.
Applications for constrained devices that have maps with 24 or fewer Applications for constrained devices that have maps with 24 or fewer
frequently used keys should consider using small integers (and those frequently used keys should consider using small integers (and those
with up to 48 frequently used keys should consider also using small with up to 48 frequently used keys should consider also using small
negative integers) because the keys can then be encoded in a single negative integers) because the keys can then be encoded in a single
byte. byte.
4.7.1. Equivalence of Keys 4.7.1. Equivalence of Keys
This notion of equivalence must be used to determine whether keys in The specific data model applying to a CBOR data item is used to
maps are duplicates or distinct. determine whether keys occurring in maps are duplicates or distinct.
o All numbers are compared by their numeric value.
* Integer data items with the same value are equal regardless of
how many bytes are used to encode them.
* Floating point data items with the same value are equal
regardless of how many bytes are used to encode them.
* An integer value encoded as a floating point data item is
equivalent to the same value encoded as an integer
o Byte strings and text strings are compared by their binary
content.
* A different length encoding has no effect on equivalence.
* A byte string is equal to a text string if they have the same
binary content.
o Two arrays are equal if all their items are in the same order and At the generic data model level, numerically equivalent integer and
equal. floating point values are distinct from each other, as they are from
the various big numbers (Tags 2 to 5). Similarly, text strings are
distinct from byte strings, even if composed of the same bytes. A
tagged value is distinct from an untagged value or from a value
tagged with a different tag.
o Two maps are equal if they have the same set of pairs regardless Within each of these groups, numeric values are distinct unless they
of their order; pairs are equal if both the key and value are are numerically equal (specifically, -0.0 is equal to 0.0); for the
equal. purpose of map key equivalence, NaN (not a number) values are
equivalent if they have the same significand after zero-extending
both significands at the right to 64 bits.
o Tags have no effect in determining equality of a data item, if two (Byte and text) strings are compared byte by byte, arrays element by
items are equal then they are equal irrespective of any tags that element, and are equal if they have the same number of bytes/elements
either or both may have. and the same values at the same positions. Two maps are equal if
they have the same set of pairs regardless of their order; pairs are
equal if both the key and value are equal.
o Simple values are equal if they simply have the same value. Tagged values are equal if both the tag and the value are equal.
Simple values are equal if they simply have the same value. Nothing
else is equal in the generic data model, a simple value 2 is not
equivalent to an integer 2 and an array is never equivalent to a map.
Nothing else is equal, a simple value 2 is not equivalent to an As discussed in Section 2.2, specific data models can make values
integer 2 and an array cannot be equivalent to a map with the same equivalent for the purpose of comparing map keys that are distinct in
values and sequential integer keys. the generic data model. Note that this implies that a generic
decoder may deliver a decoded map to an application that needs to be
checked for duplicate map keys by that application (alternatively,
the decoder may provide a programming interface to perform this
service for the application). Specific data models cannot
distinguish values for map keys that are equal for this purpose at
the generic data model level.
4.8. Undefined Values 4.8. Undefined Values
In some CBOR-based protocols, the simple value (Section 3.3) of In some CBOR-based protocols, the simple value (Section 3.3) of
Undefined might be used by an encoder as a substitute for a data item Undefined might be used by an encoder as a substitute for a data item
with an encoding problem, in order to allow the rest of the enclosing with an encoding problem, in order to allow the rest of the enclosing
data items to be encoded without harm. data items to be encoded without harm.
4.9. Canonical CBOR 4.9. Preferred Serialization
For some values at the data model level, CBOR provides multiple
serializations. For many applications, it is desirable that an
encoder always chooses a preferred serialization; however, the
present specification does not put the burden of enforcing this
preference on either encoder or decoder.
Some constrained decoders may be limited in their ability to decode
non-preferred serializations: For example, if only integers below
1_000_000_000 are expected in an application, the decoder may leave
out the code that would be needed to decode 64-bit arguments in
integers. An encoder that always uses preferred serialization
("preferred encoder") interoperates with this decoder for the numbers
that can occur in this application. More generally speaking, it
therefore can be said that a preferred encoder is more universally
interoperable (and also less wasteful) than one that, say, always
uses 64-bit integers.
Similarly, a constrained encoder may be limited in the variety of
representation variants it supports in such a way that it does not
emit preferred serializations ("variant encoder"): Say, it could be
designed to always use the 32-bit variant for an integer that it
encodes even if a short representation is available (again, assuming
that there is no application need for integers that can only be
represented with the 64-bit variant). A decoder that does not rely
on only ever receiving preferred serializations ("variation-tolerant
decoder") can there be said to be more universally interoperable (it
might very well optimize for the case of receiving preferred
serializations, though). Full implementations of CBOR decoders are
by definition variation-tolerant; the distinction is only relevant if
a constrained implementation of a CBOR decoder meets a variant
encoder.
The preferred serialization always uses the shortest form of
representing the argument (Section 3)); it also uses the shortest
floating point encoding that preserves the value being encoded (see
Section 4.6). Definite length encoding is preferred whenever the
length is known at the time the serialization of the item starts.
4.10. Canonical CBOR
Some protocols may want encoders to only emit CBOR in a particular Some protocols may want encoders to only emit CBOR in a particular
canonical format; those protocols might also have the decoders check canonical format; those protocols might also have the decoders check
that their input is canonical. Those protocols are free to define that their input is canonical. Those protocols are free to define
what they mean by a canonical format and what encoders and decoders what they mean by a canonical format and what encoders and decoders
are expected to do. This section defines a set of restrictions that are expected to do. This section defines a set of restrictions that
can serve as the base of such a canonical format. can serve as the base of such a canonical format.
A CBOR encoding satisfies the "core canonicalization requirements" if A CBOR encoding satisfies the "core canonicalization requirements" if
it satisfies the following restrictions: it satisfies the following restrictions:
o Integers MUST be as short as possible. In particular: o Arguments (see Section 3) for integers, lengths in major types 2
through 5, and tags MUST be as short as possible. In particular:
* 0 to 23 and -1 to -24 MUST be expressed in the same byte as the * 0 to 23 and -1 to -24 MUST be expressed in the same byte as the
major type; major type;
* 24 to 255 and -25 to -256 MUST be expressed only with an * 24 to 255 and -25 to -256 MUST be expressed only with an
additional uint8_t; additional uint8_t;
* 256 to 65535 and -257 to -65536 MUST be expressed only with an * 256 to 65535 and -257 to -65536 MUST be expressed only with an
additional uint16_t; additional uint16_t;
* 65536 to 4294967295 and -65537 to -4294967296 MUST be expressed * 65536 to 4294967295 and -65537 to -4294967296 MUST be expressed
only with an additional uint32_t. only with an additional uint32_t.
o The expression of lengths in major types 2 through 5 MUST be as
short as possible. The rules for these lengths follow the above
rule for integers.
o The keys in every map MUST be sorted in the bytewise lexicographic o The keys in every map MUST be sorted in the bytewise lexicographic
order of their canonical encodings. For example, the following order of their canonical encodings. For example, the following
keys are sorted correctly: keys are sorted correctly:
1. 10, encoded as 0x0a. 1. 10, encoded as 0x0a.
2. 100, encoded as 0x1864. 2. 100, encoded as 0x1864.
3. -1, encoded as 0x20. 3. -1, encoded as 0x20.
skipping to change at page 31, line 17 skipping to change at page 33, line 15
2. Encode all values as the smallest of 16-, 32-, or 64-bit 2. Encode all values as the smallest of 16-, 32-, or 64-bit
floating point that accurately represents the value, even for floating point that accurately represents the value, even for
integral values, or integral values, or
3. Encode all values as 64-bit floating point. 3. Encode all values as 64-bit floating point.
If NaN is an allowed value, the protocol needs to pick a single If NaN is an allowed value, the protocol needs to pick a single
representation, for example 0xf97e00. representation, for example 0xf97e00.
o If a protocol includes a field that can express integers larger o If a protocol includes a field that can express integers larger
than 2^64 using tag 2 (Section 3.4.2), the protocol's than 2^64 using tag 2 (Section 3.4.4), the protocol's
canonicalization needs to specify whether small integers are canonicalization needs to specify whether small integers are
expressed using the tag or major types 0 and 1. expressed using the tag or major types 0 and 1.
o A protocol might give encoders the choice of representing a URL as o A protocol might give encoders the choice of representing a URL as
either a text string or, using Section 3.4.4.3, tag 32 containing either a text string or, using Section 3.4.6.3, tag 32 containing
a text string. This protocol's canonicalization needs to either a text string. This protocol's canonicalization needs to either
require that the tag is present or require that it's absent, not require that the tag is present or require that it's absent, not
allow either one. allow either one.
4.9.1. Length-first map key ordering 4.10.1. Length-first map key ordering
The core canonicalization requirements sort map keys in a different The core canonicalization requirements sort map keys in a different
order from the one suggested by [RFC7049]. Protocols that need to be order from the one suggested by [RFC7049]. Protocols that need to be
compatible with [RFC7049]'s order can instead be specified in terms compatible with [RFC7049]'s order can instead be specified in terms
of this specification's "length-first core canonicalization of this specification's "length-first core canonicalization
requirements": requirements":
A CBOR encoding satisfies the "length-first core canonicalization A CBOR encoding satisfies the "length-first core canonicalization
requirements" if it satisfies the core canonicalization requirements requirements" if it satisfies the core canonicalization requirements
except that the keys in every map MUST be sorted such that: except that the keys in every map MUST be sorted such that:
skipping to change at page 32, line 17 skipping to change at page 34, line 13
4. 100, encoded as 0x1864. 4. 100, encoded as 0x1864.
5. "z", encoded as 0x617a. 5. "z", encoded as 0x617a.
6. [-1], encoded as 0x8120. 6. [-1], encoded as 0x8120.
7. "aa", encoded as 0x626161. 7. "aa", encoded as 0x626161.
8. [100], encoded as 0x811864. 8. [100], encoded as 0x811864.
4.10. Strict Mode 4.11. Strict Mode
Some areas of application of CBOR do not require canonicalization Some areas of application of CBOR do not require canonicalization
(Section 4.9) but may require that different decoders reach the same (Section 4.10) but may require that different decoders reach the same
(semantically equivalent) results, even in the presence of (semantically equivalent) results, even in the presence of
potentially malicious data. This can be required if one application potentially malicious data. This can be required if one application
(such as a firewall or other protecting entity) makes a decision (such as a firewall or other protecting entity) makes a decision
based on the data that another application, which independently based on the data that another application, which independently
decodes the data, relies on. decodes the data, relies on.
Normally, it is the responsibility of the sender to avoid ambiguously Normally, it is the responsibility of the sender to avoid ambiguously
decodable data. However, the sender might be an attacker specially decodable data. However, the sender might be an attacker specially
making up CBOR data such that it will be interpreted differently by making up CBOR data such that it will be interpreted differently by
different decoders in an attempt to exploit that as a vulnerability. different decoders in an attempt to exploit that as a vulnerability.
skipping to change at page 42, line 38 skipping to change at page 44, line 32
Applications where a CBOR data item is examined by a gatekeeper Applications where a CBOR data item is examined by a gatekeeper
function and later used by a different application may exhibit function and later used by a different application may exhibit
vulnerabilities when multiple interpretations of the data item are vulnerabilities when multiple interpretations of the data item are
possible. For example, an attacker could make use of duplicate keys possible. For example, an attacker could make use of duplicate keys
in maps and precision issues in numbers to make the gatekeeper base in maps and precision issues in numbers to make the gatekeeper base
its decisions on a different interpretation than the one that will be its decisions on a different interpretation than the one that will be
used by the second application. Protocols that are used in a used by the second application. Protocols that are used in a
security context should be defined in such a way that these multiple security context should be defined in such a way that these multiple
interpretations are reliably reduced to a single one. To facilitate interpretations are reliably reduced to a single one. To facilitate
this, encoder and decoder implementations used in such contexts this, encoder and decoder implementations used in such contexts
should provide at least one strict mode of operation (Section 4.10). should provide at least one strict mode of operation (Section 4.11).
10. Acknowledgements 10. Acknowledgements
CBOR was inspired by MessagePack. MessagePack was developed and CBOR was inspired by MessagePack. MessagePack was developed and
promoted by Sadayuki Furuhashi ("frsyuki"). This reference to promoted by Sadayuki Furuhashi ("frsyuki"). This reference to
MessagePack is solely for attribution; CBOR is not intended as a MessagePack is solely for attribution; CBOR is not intended as a
version of or replacement for MessagePack, as it has different design version of or replacement for MessagePack, as it has different design
goals and requirements. goals and requirements.
The need for functionality beyond the original MessagePack The need for functionality beyond the original MessagePack
skipping to change at page 43, line 13 skipping to change at page 45, line 6
MessagePack that was developed by Eric Zhang for the binaryjs MessagePack that was developed by Eric Zhang for the binaryjs
project. A similar, but different, extension was made by Tim Caswell project. A similar, but different, extension was made by Tim Caswell
for his msgpack-js and msgpack-js-browser projects. Many people have for his msgpack-js and msgpack-js-browser projects. Many people have
contributed to the recent discussion about extending MessagePack to contributed to the recent discussion about extending MessagePack to
separate text string representation from byte string representation. separate text string representation from byte string representation.
The encoding of the additional information in CBOR was inspired by The encoding of the additional information in CBOR was inspired by
the encoding of length information designed by Klaus Hartke for CoAP. the encoding of length information designed by Klaus Hartke for CoAP.
This document also incorporates suggestions made by many people, This document also incorporates suggestions made by many people,
notably Dan Frost, James Manger, Joe Hildebrand, Keith Moore, Matthew notably Dan Frost, James Manger, Joe Hildebrand, Keith Moore,
Lepinski, Nico Williams, Phillip Hallam-Baker, Ray Polk, Tim Bray, Laurence Lundblade, Matthew Lepinski, Michael Richardson, Nico
Tony Finch, Tony Hansen, and Yaron Sheffer. Williams, Phillip Hallam-Baker, Ray Polk, Tim Bray, Tony Finch, Tony
Hansen, and Yaron Sheffer.
11. References 11. References
11.1. Normative References 11.1. Normative References
[ECMA262] Ecma International, "ECMAScript 2018 Language [ECMA262] Ecma International, "ECMAScript 2018 Language
Specification", ECMA Standard ECMA-262, 9th Edition, June Specification", ECMA Standard ECMA-262, 9th Edition, June
2018, <https://www.ecma- 2018, <https://www.ecma-
international.org/publications/files/ECMA-ST/ international.org/publications/files/ECMA-ST/
Ecma-262.pdf>. Ecma-262.pdf>.
[IEEE.754.2008]
Institute of Electrical and Electronics Engineers, "IEEE
Standard for Floating-Point Arithmetic", IEEE
Standard 754-2008, August 2008.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996, Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
<https://www.rfc-editor.org/info/rfc2045>. <https://www.rfc-editor.org/info/rfc2045>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
skipping to change at page 44, line 38 skipping to change at page 46, line 34
Encoding Rules (BER), Canonical Encoding Rules (CER) and Encoding Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER)", ITU-T Recommendation Distinguished Encoding Rules (DER)", ITU-T Recommendation
X.690, 1994. X.690, 1994.
[BSON] Various, "BSON - Binary JSON", 2013, [BSON] Various, "BSON - Binary JSON", 2013,
<http://bsonspec.org/>. <http://bsonspec.org/>.
[MessagePack] [MessagePack]
Furuhashi, S., "MessagePack", 2013, <http://msgpack.org/>. Furuhashi, S., "MessagePack", 2013, <http://msgpack.org/>.
[PCRE] Hazel, P., "PCRE - Perl Compatible Regular Expressions", [PCRE] Ho, A., "PCRE - Perl Compatible Regular Expressions",
2018, <http://www.pcre.org/>. 2018, <http://www.pcre.org/>.
[RFC0713] Haverty, J., "MSDTP-Message Services Data Transmission [RFC0713] Haverty, J., "MSDTP-Message Services Data Transmission
Protocol", RFC 713, DOI 10.17487/RFC0713, April 1976, Protocol", RFC 713, DOI 10.17487/RFC0713, April 1976,
<https://www.rfc-editor.org/info/rfc713>. <https://www.rfc-editor.org/info/rfc713>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13, Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013, RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>. <https://www.rfc-editor.org/info/rfc6838>.
skipping to change at page 45, line 15 skipping to change at page 47, line 15
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228, Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014, DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/info/rfc7228>. <https://www.rfc-editor.org/info/rfc7228>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259, Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017, DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>. <https://www.rfc-editor.org/info/rfc8259>.
[UBJSON] The Buzz Media, "Universal Binary JSON Specification",
2013, <http://ubjson.org/>.
[YAML] Ben-Kiki, O., Evans, C., and I. Net, "YAML Ain't Markup [YAML] Ben-Kiki, O., Evans, C., and I. Net, "YAML Ain't Markup
Language (YAML[TM]) Version 1.2", 3rd Edition, October Language (YAML[TM]) Version 1.2", 3rd Edition, October
2009, <http://www.yaml.org/spec/1.2/spec.html>. 2009, <http://www.yaml.org/spec/1.2/spec.html>.
Appendix A. Examples Appendix A. Examples
The following table provides some CBOR-encoded values in hexadecimal The following table provides some CBOR-encoded values in hexadecimal
(right column), together with diagnostic notation for these values (right column), together with diagnostic notation for these values
(left column). Note that the string "\u00fc" is one form of (left column). Note that the string "\u00fc" is one form of
diagnostic notation for a UTF-8 string containing the single Unicode diagnostic notation for a UTF-8 string containing the single Unicode
skipping to change at page 52, line 15 skipping to change at page 54, line 15
| | | | | |
| 0xba | map (four-byte uint32_t for n, and then n pairs of | | 0xba | map (four-byte uint32_t for n, and then n pairs of |
| | data items follow) | | | data items follow) |
| | | | | |
| 0xbb | map (eight-byte uint64_t for n, and then n pairs of | | 0xbb | map (eight-byte uint64_t for n, and then n pairs of |
| | data items follow) | | | data items follow) |
| | | | | |
| 0xbf | map, pairs of data items follow, terminated by | | 0xbf | map, pairs of data items follow, terminated by |
| | "break" | | | "break" |
| | | | | |
| 0xc0 | Text-based date/time (data item follows; see | | 0xc0 | Text-based date/time (data item follows; see Section |
| | Section 3.4.1) | | | 3.4.2) |
| | | | | |
| 0xc1 | Epoch-based date/time (data item follows; see | | 0xc1 | Epoch-based date/time (data item follows; see |
| | Section 3.4.1) | | | Section 3.4.3) |
| | | | | |
| 0xc2 | Positive bignum (data item "byte string" follows) | | 0xc2 | Positive bignum (data item "byte string" follows) |
| | | | | |
| 0xc3 | Negative bignum (data item "byte string" follows) | | 0xc3 | Negative bignum (data item "byte string" follows) |
| | | | | |
| 0xc4 | Decimal Fraction (data item "array" follows; see | | 0xc4 | Decimal Fraction (data item "array" follows; see |
| | Section 3.4.3) | | | Section 3.4.5) |
| | | | | |
| 0xc5 | Bigfloat (data item "array" follows; see | | 0xc5 | Bigfloat (data item "array" follows; see Section |
| | Section 3.4.3) | | | 3.4.5) |
| | | | | |
| 0xc6..0xd4 | (tagged item) | | 0xc6..0xd4 | (tagged item) |
| | | | | |
| 0xd5..0xd7 | Expected Conversion (data item follows; see | | 0xd5..0xd7 | Expected Conversion (data item follows; see Section |
| | Section 3.4.4.2) | | | 3.4.6.2) |
| | | | | |
| 0xd8..0xdb | (more tagged items, 1/2/4/8 bytes and then a data | | 0xd8..0xdb | (more tagged items, 1/2/4/8 bytes and then a data |
| | item follow) | | | item follow) |
| | | | | |
| 0xe0..0xf3 | (simple value) | | 0xe0..0xf3 | (simple value) |
| | | | | |
| 0xf4 | False | | 0xf4 | False |
| | | | | |
| 0xf5 | True | | 0xf5 | True |
| | | | | |
skipping to change at page 55, line 33 skipping to change at page 57, line 33
*p++ = mt + 24; *p++ = mt + 24;
*p++ = ui; *p++ = ui;
} else } else
... ...
Figure 2: Pseudocode for Encoding a Signed Integer Figure 2: Pseudocode for Encoding a Signed Integer
Appendix D. Half-Precision Appendix D. Half-Precision
As half-precision floating-point numbers were only added to IEEE 754 As half-precision floating-point numbers were only added to IEEE 754
in 2008, today's programming platforms often still only have limited in 2008 [IEEE.754.2008], today's programming platforms often still
support for them. It is very easy to include at least decoding only have limited support for them. It is very easy to include at
support for them even without such support. An example of a small least decoding support for them even without such support. An
decoder for half-precision floating-point numbers in the C language example of a small decoder for half-precision floating-point numbers
is shown in Figure 3. A similar program for Python is in Figure 4; in the C language is shown in Figure 3. A similar program for Python
this code assumes that the 2-byte value has already been decoded as is in Figure 4; this code assumes that the 2-byte value has already
an (unsigned short) integer in network byte order (as would be done been decoded as an (unsigned short) integer in network byte order (as
by the pseudocode in Appendix C). would be done by the pseudocode in Appendix C).
#include <math.h> #include <math.h>
double decode_half(unsigned char *halfp) { double decode_half(unsigned char *halfp) {
int half = (halfp[0] << 8) + halfp[1]; int half = (halfp[0] << 8) + halfp[1];
int exp = (half >> 10) & 0x1f; int exp = (half >> 10) & 0x1f;
int mant = half & 0x3ff; int mant = half & 0x3ff;
double val; double val;
if (exp == 0) val = ldexp(mant, -24); if (exp == 0) val = ldexp(mant, -24);
else if (exp != 31) val = ldexp(mant + 1024, exp - 25); else if (exp != 31) val = ldexp(mant + 1024, exp - 25);
skipping to change at page 58, line 19 skipping to change at page 60, line 19
[BSON] is a data format that was developed for the storage of JSON- [BSON] is a data format that was developed for the storage of JSON-
like maps (JSON objects) in the MongoDB database. Its major like maps (JSON objects) in the MongoDB database. Its major
distinguishing feature is the capability for in-place update, distinguishing feature is the capability for in-place update,
foregoing a compact representation. BSON uses a counted foregoing a compact representation. BSON uses a counted
representation except for map keys, which are null-byte terminated. representation except for map keys, which are null-byte terminated.
While BSON can be used for the representation of JSON-like objects on While BSON can be used for the representation of JSON-like objects on
the wire, its specification is dominated by the requirements of the the wire, its specification is dominated by the requirements of the
database application and has become somewhat baroque. The status of database application and has become somewhat baroque. The status of
how BSON extensions will be implemented remains unclear. how BSON extensions will be implemented remains unclear.
E.4. UBJSON E.4. MSDTP: RFC 713
[UBJSON] has a design goal to make JSON faster and somewhat smaller,
using a binary format that is limited to exactly the data model JSON
uses. Thus, there is expressly no intention to support, for example,
binary data; however, there is a "high-precision number", expressed
as a character string in JSON syntax. UBJSON is not optimized for
code compactness, and its type byte coding is optimized for human
recognition and not for compact representation of native types such
as small integers. Although UBJSON is mostly counted, it provides a
reserved "unknown-length" value to support streaming of arrays and
maps (JSON objects). Within these containers, UBJSON also has a
"Noop" type for padding.
E.5. MSDTP: RFC 713
Message Services Data Transmission (MSDTP) is a very early example of Message Services Data Transmission (MSDTP) is a very early example of
a compact message format; it is described in [RFC0713], written in a compact message format; it is described in [RFC0713], written in
1976. It is included here for its historical value, not because it 1976. It is included here for its historical value, not because it
was ever widely used. was ever widely used.
E.6. Conciseness on the Wire E.5. Conciseness on the Wire
While CBOR's design objective of code compactness for encoders and While CBOR's design objective of code compactness for encoders and
decoders is a higher priority than its objective of conciseness on decoders is a higher priority than its objective of conciseness on
the wire, many people focus on the wire size. Table 6 shows some the wire, many people focus on the wire size. Table 6 shows some
encoding examples for the simple nested array [1, [2, 3]]; where some encoding examples for the simple nested array [1, [2, 3]]; where some
form of indefinite-length encoding is supported by the encoding, form of indefinite-length encoding is supported by the encoding,
[_ 1, [2, 3]] (indefinite length on the outer array) is also shown. [_ 1, [2, 3]] (indefinite length on the outer array) is also shown.
+-------------+--------------------------+--------------------------+ +-------------+--------------------------+--------------------------+
| Format | [1, [2, 3]] | [_ 1, [2, 3]] | | Format | [1, [2, 3]] | [_ 1, [2, 3]] |
skipping to change at page 59, line 21 skipping to change at page 61, line 21
| | 01 02 02 01 03 | 01 02 02 01 03 00 00 | | | 01 02 02 01 03 | 01 02 02 01 03 00 00 |
| | | | | | | |
| MessagePack | 92 01 92 02 03 | | | MessagePack | 92 01 92 02 03 | |
| | | | | | | |
| BSON | 22 00 00 00 10 30 00 01 | | | BSON | 22 00 00 00 10 30 00 01 | |
| | 00 00 00 04 31 00 13 00 | | | | 00 00 00 04 31 00 13 00 | |
| | 00 00 10 30 00 02 00 00 | | | | 00 00 10 30 00 02 00 00 | |
| | 00 10 31 00 03 00 00 00 | | | | 00 10 31 00 03 00 00 00 | |
| | 00 00 | | | | 00 00 | |
| | | | | | | |
| UBJSON | 61 02 42 01 61 02 42 02 | 61 ff 42 01 61 02 42 02 |
| | 42 03 | 42 03 45 |
| | | |
| CBOR | 82 01 82 02 03 | 9f 01 82 02 03 ff | | CBOR | 82 01 82 02 03 | 9f 01 82 02 03 ff |
+-------------+--------------------------+--------------------------+ +-------------+--------------------------+--------------------------+
Table 6: Examples for Different Levels of Conciseness Table 6: Examples for Different Levels of Conciseness
Appendix F. Changes from RFC 7049 Appendix F. Changes from RFC 7049
The following is a list of known changes from RFC 7049. This list is The following is a list of known changes from RFC 7049. This list is
non-authoritative. It is meant to help reviewers see the significant non-authoritative. It is meant to help reviewers see the significant
differences. differences.
 End of changes. 71 change blocks. 
211 lines changed or deleted 280 lines changed or added

This html diff was produced by rfcdiff 1.47. The latest version is available from http://tools.ietf.org/tools/rfcdiff/