DateKeys/spec/datekeys.cddl

; DateKeys Protocol Specification v0.8.2 - CBOR schemas (RFC 8610 CDDL).
;
; Normative companion of spec/DateKeys_Protocol_Specification_v0.8.2.md, as
; implemented by the reference implementation g.activething.com/go/DateKeys.
;
; Encoding rules that CDDL cannot express (spec section 58, 58.1):
;   - Every structure uses the CBOR profile of the protocol (spec section 58):
;     Deterministic CBOR (RFC 8949 section 4.2.1) restricted to major types 0,
;     2, 3, 4 and 5, with unsigned integer map keys in strictly ascending
;     order, shortest-form integers and lengths, definite lengths only and
;     valid UTF-8 text. Negative integers, tags, floats, simple values
;     (including null) and indefinite lengths are rejected.
;   - A decoder re-encodes what it decoded and rejects any byte difference
;     (ERR_NON_CANONICAL_CBOR).
;   - A semantically absent optional field is omitted. Empty arrays, empty
;     maps, null, "" and h'' never stand for absence; the .size and non-empty
;     constraints below make those forms invalid.
;   - Maps are closed: keys not listed here are rejected. New semantics go in
;     extensions (spec section 54).
;   - Within one object an extension_id appears at most once and never in both
;     extension arrays; arrays are sorted by the UTF-8 bytes of extension_id.
;   - A violation of a normative rule of this schema, including .size,
;     integer ranges and the 64-extension maximum, is ERR_NON_CANONICAL_CBOR
;     unless spec section 57 names a more specific error (schema version,
;     compact_datekey, access_type and access_material, Provider Profile
;     names and public key). The implementation limits marked below are not
;     normative (spec section 74); an implementation that applies them uses
;     the same mapping.

; Spec section 11 and 12.
provider-profile = {
  0 => "datekeys-provider-profile",
  1 => 1,
  2 => profile-id,
  3 => name,               ; provider, "drand"
  4 => name,               ; provider network identifier, "quicknet"
  5 => bstr .size 32,      ; chain_hash
  6 => public-key,         ; group public key
  7 => 1..max-safe-uint,   ; period in seconds
  8 => 0..max-safe-uint,   ; genesis_time, Unix seconds
  9 => name,               ; scheme, "bls-unchained-g1-rfc9380"
  10 => bstr .size 32,     ; genesis_seed
}

; Spec section 24. Stored as exact bytes after the 16-byte PRELUDE and covered
; by header_binding = SHA-256(PRELUDE || PUBLIC_HEADER).
public-header = {
  0 => "datekeycap",
  1 => 1,
  2 => capsule-id,
  3 => compact-datekey,    ; the only source of the profile
  4 => access-policy,
  ? 5 => extensions,       ; critical_extensions
  ? 6 => extensions,       ; noncritical_extensions
}

; Spec section 31. Sealed inside OUTER_TIME_AGE (time_only) or inside
; INNER_ACCESS_AGE inside OUTER_TIME_AGE (time_and_key).
control = {
  0 => "datekeys-control",
  1 => 1,
  2 => bstr .size 32,      ; header_binding
  3 => bstr .size 32,      ; payload_identity, raw X25519 identity I_PAYLOAD
  ? 4 => extensions,       ; critical_extensions
  ? 5 => extensions,       ; noncritical_extensions
}

; Spec section 41. BODY_CBOR of a .dkk, after the 12-byte DKK1 prelude.
access-key-body = {
  0 => "datekeys-access-key",
  1 => 1,
  2 => bstr .size 16,      ; credential_id
  3 => capsule-id,
  4 => access-type,
  5 => access-material,
  ? 6 => verification-metadata,
  ? 7 => extensions,       ; critical_extensions
  ? 8 => extensions,       ; noncritical_extensions
}

; Spec section 43. Present only when it holds a digest: never an empty map.
verification-metadata = {
  0 => bstr .size 32,      ; capsule_digest = SHA-256(exact .dkc bytes)
}

; Spec section 31 and 54.
extensions = [1*64 extension]
extension = {
  0 => extension-id,
  1 => extension-version,
  ? 2 => extension-data,
}
extension-version = uint .le 4294967295
; Opaque bytes: the base protocol never decodes or validates the content, and
; an extension without data omits key 2. The effective bound is the frame of
; the containing object (spec section 57); 67108864 bytes (64 MiB) is the
; largest frame, SEALED_CONTROL. Each registered extension declares its own
; maximum (spec section 72).
extension-data = bstr .size (1..67108864)

capsule-id = bstr .size 16
access-policy = &(time_only: 0, time_and_key: 1)
access-type = "x25519"
access-material = bstr .size 32   ; for access-type "x25519"

; 2^53-1: every unsigned integer of the protocol is exact as an IEEE 754
; double (spec section 58).
max-safe-uint = 9007199254740991

; Implementation limits of the reference implementation (spec section 74
; leaves definitive field limits open).
profile-id = tstr .regexp "[a-z0-9][a-z0-9:._-]{0,127}"
name = tstr .regexp "[a-z0-9][a-z0-9._-]{0,63}"
public-key = bstr .size (1..1024)
extension-id = tstr .size (1..256)

; Spec section 18 and 19: "dk1_" + unpadded Base64URL of the canonical JSON
; {"version":1,"network":<profile-id>,"round":<round>}, round in 1..2^53-1.
compact-datekey = tstr .regexp "dk1_[A-Za-z0-9_-]+"