Deterministic and Secure CBOR Encoding and Decoding

Encodes R values as Concise Binary Object Representation (CBOR, RFC 8949; Bormann and Hoffman (2020) ) and decodes CBOR into ordinary R vectors and lists. Decoding checks the whole input against configurable depth, size and item limits before any R object is built, so untrusted input from network peers and devices cannot drive large allocations. Encoding is deterministic: identical R objects always produce identical bytes. Uses a bundled copy of the 'TinyCBOR' library (< https://github.com/intel/tinycbor>), so no system library is required.

zucbor

zucbor encodes and decodes CBOR (RFC 8949), the binary counterpart of JSON, to and from ordinary R vectors and lists. It is built for input you do not trust — COSE and CWT tokens, WebAuthn passkey data, CoAP device telemetry — and for output that must be byte-exact.

• Decoding checks the whole input before building anything. Well-formedness, UTF-8, tag content, duplicate map keys and configurable depth, size and item limits are all enforced first, so a length header can never make R allocate for data the input does not contain.
• Encoding is deterministic. Identical R objects give identical bytes on every platform (RFC 8949 core deterministic encoding), and decoding then re-encoding deterministic input gives back exactly the same bytes — what a signature over CBOR needs.
• Values keep their meaning. Integers stay exact beyond 2^53, byte strings stay raw, maps with integer keys stay maps, dates become POSIXct and Date.
• No system library. A subset of TinyCBOR is bundled; the encoder and the diagnostic printer are zucbor's own.

Installation

install.packages("zucbor")

# or the development version:
# install.packages("pak")
pak::pak("pedrobtz/zucbor")

Building from source needs a C compiler; with GCC, version 11 or newer (older GCC rejects a construct in the bundled TinyCBOR 7.0).

Decoding

library(zucbor)

cbor_decode(as.raw(c(0xa2, 0x61, 0x61, 0x01, 0x61, 0x62, 0x82, 0x02, 0x03)))
#> $a
#> [1] 1
#>
#> $b
#> [1] 2 3

A map whose keys are not all text — a COSE header, say — is a cbor_map, never a list with the keys quietly turned into names:

cbor_decode(as.raw(c(0xa2, 0x01, 0x26, 0x04, 0x42, 0x31, 0x31)))
#> <cbor_map: 2 entries>
#> [[1]]
#> [1] -7
#> [[4]]
#> [1] 31 31

Hostile input fails with a classed condition, before any R object exists:

# An array header claiming 2^64 - 1 elements, in nine bytes.
tryCatch(cbor_decode(as.raw(c(0x9b, rep(0xff, 8)))),
         zucbor_error = function(e) class(e)[1])
#> [1] "zucbor_parse_error"

# The same key twice, once in a longer encoding: refused by value.
cbor_validate(as.raw(c(0xa2, 0x01, 0x00, 0x18, 0x01, 0x00)))
#> [1] FALSE

Encoding

b <- cbor_encode(list(alg = -7, kid = charToRaw("11"),
                      when = as.POSIXct("2026-01-01", tz = "UTC")))
b
#>  [1] a3 63 61 6c 67 26 63 6b 69 64 42 31 31 64 77 68 65 6e c1 1a 69 55 b9 00

cbor_diagnose(b)
#> [1] "{\"alg\": -7, \"kid\": h'3131', \"when\": 1(1767225600)}"

# Deterministic: map entries are sorted by their encoded keys.
identical(cbor_encode(list(b = 1, a = 2)), cbor_encode(list(a = 2, b = 1)))
#> [1] TRUE

-7 is a double in R, but it is written as the integer a COSE algorithm identifier must be: a whole double is always an integer in CBOR.

What zucbor is not

It decodes and encodes CBOR. It does not verify COSE signatures, validate against CDDL schemas, or decode base64: those belong to other packages.

Learn more

• vignette("untrusted", package = "zucbor"): limits, duplicate keys and deterministic input.
• vignette("cose-webauthn", package = "zucbor"): WebAuthn attestation objects, COSE keys and signed structures.
• Examples: worked examples for COSE keys, wide integers, dates, embedded CBOR, telemetry, files and limits.
• ?cbor_decode and ?cbor_encode state the full mapping between CBOR and R.

zucbor is one of the zu* packages, with zujson, zuyaml and zuxml.