CBOR Object Type Extension (COTE)

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Table of Contents

1. Introduction

This specification introduces a method for augmenting data expressed in the CBOR [RFC8949] notation, with a universal type identifier mechanism.¶

The primary purpose is to enable developers defining community- or application-specific type identifiers without having to go through an IANA registration process. Although the scheme imposes no restrictions on type identifiers (beyond being valid CBOR data items), using URLs should due to their ubiquity be a candidate for CBOR based standards.¶

Since the type identifier scheme is supposed to be an integral part of CBOR data items, compliant items may also be embedded in other CBOR and non-CBOR constructs, as well as stored in databases without any additional information.¶

If applied to top level items, the type identifier scheme may also reduce the need for application specific media types. In many cases "application/cbor" should suffice.¶

2. Specification

This specification builds on the CBOR [RFC8949] tag feature (major type 6), by defining a fixed tag with the preliminary decimal value of 211.¶

This tag MUST in turn enclose a CBOR array with two elements, where the first element contains an object identifier, while the second holds the object data itself. Illustrated in CBOR diagnostic notation (section 8 of [RFC8949]) this becomes:¶

    211([Object Identifier, Object])¶

Both arguments may be any valid CBOR object.¶

Note that real-world usages will typically impose constraints like requiring object identifiers to be expressed as https URLs etc.¶

    211(["https://example.com/myobject", {
      1: "data",
      2: "more data"
    }])

D8 D3                               # tag(211)
   82                               # array(2)
      78 1C                         # text(28)
         68747470733A2F2F6578616D706C652E636F6D2F6D796F626A656374
                                    # "https://example.com/myobject"
      A2                            # map(2)
         01                         # unsigned(1)
         64                         # text(4)
            64617461                # "data"
         02                         # unsigned(2)
         69                         # text(9)
            6D6F72652064617461      # "more data"

3. IANA Considerations

In the registry [IANA.cbor-tags], IANA is requested to allocate the tag defined in Table 1.¶

4. Security Considerations

This specification inherits all the security considerations of CBOR [RFC8949].¶

URL-based type identifiers MUST NOT be used for automatically downloading possible CBOR schemas to CBOR processors, since this introduces potential vulnerabilities. A RECOMMENDED way deploying URL-based type identifiers is as hyper-links to human-readable information gathered through Web browsers.¶

The availability of type information does in no way limit the need for input data validation.¶

For signed CBOR objects, it is RECOMMENDED to include the type identifier extension in the signature calculation as well. The same considerations apply to encryption using AEAD algorithms.¶

Acknowledgements

People who have contributed directly and indirectly with valuable input to this specification include TBD¶

Document History

[[ This section to be removed by the RFC Editor before publication as an RFC ]]¶

Version 00:¶

• Initial publication.¶

Author's Address