DateKeys/spec/datekeys.cddl

; DateKeys Protocol Specification v0.11 (working draft) - CBOR schemas (RFC
; 8610 CDDL).
;
; Normative companion of spec/DateKeys_Protocol_Specification_v0.11.md. The
; reference implementation g.activething.com/go/DateKeys still implements
; v0.9, whose schemas are in tag spec-v0.9. These schemas include the three
; control versions: 1, of capsule format 1 (v0.8.2), 2, of format 2 (v0.9),
; and 3, of format 3, and the security and head objects of format 3.
;
; 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).
;   - The elements of each extension array are in strictly ascending order of
;     the UTF-8 bytes of extension_id (spec section 54): bytes compared as
;     unsigned integers, the first differing byte decides and a proper prefix
;     sorts first; never UTF-16 code units, case folding, Unicode
;     normalization or a locale collation. U+FF61 (ef bd a1) sorts before
;     U+10000 (f0 90 80 80). The strict order also forbids a repeated
;     extension_id within an array, and no extension_id appears in both
;     arrays of one object, so an extension_id appears at most once per
;     object.
;   - 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). Those rules are checked with the fields, after
;     the rest of this schema; here a field needs only the CBOR type of its
;     rule, and another type is ERR_NON_CANONICAL_CBOR. The implementation
;     limits marked below are not normative; spec section 74 lists them,
;     with the limits of the reference outside this schema, and an
;     implementation that applies them uses the same mapping.
;   - The schema version of a control (key 1) is the one spec section 22
;     assigns to the format of its capsule, the VERSION of the PRELUDE:
;     control-v1 only in format 1, control-v2 only in format 2 and
;     control-v3 only in format 3. A decoder
;     picks the rule by the format, and another version is
;     ERR_UNSUPPORTED_VERSION, read before the rest of the schema (spec
;     section 69.1, layer 2). CDDL cannot express that link.
;   - payload-length holds L as an unsigned 64-bit big-endian integer in
;     exactly 8 bytes, whatever its value, and a decoder reads all 8 bytes;
;     the value is at most max-payload-length (spec section 29.1, 31). A
;     larger value is ERR_NON_CANONICAL_CBOR, like any rule of this schema.
;   - When bytes break several rules, the code is the one of the first
;     failing layer (spec section 69.1): frame, then type tag and schema
;     version (keys 0 and 1; for a control, the version of its capsule
;     format), then this schema, then the fields with codes of their own in
;     ascending key order.
;   - In format 3, security and head sit inside BODY, the plaintext of
;     PAYLOAD_AGE (spec section 29.2), whose 12-byte frame (AREA_LEN,
;     SECURITY_LEN, HEAD_LEN) CDDL cannot express. A failure of security
;     never has an error code: it only changes the verdicts (spec section
;     29.3, 29.7). In head, path lengths (R1) and the path order (R8) are
;     rules of this schema (ERR_NON_CANONICAL_CBOR); the other path rules
;     and the text rules are checked with the fields (ERR_HEAD_INVALID,
;     spec section 29.4 to 29.6), and the paths sort by their UTF-8 bytes,
;     like extension_id.

; Spec section 11 and 12. Spec section 12.1 adds the rules a profile must
; follow to be pinned (ERR_UNKNOWN_PROFILE), among them period at most 2^32-1
; and a public key that is the canonical encoding (spec section 12.2) of a
; point of the key group of the scheme, 48 or 96 bytes, other than the point
; at infinity, and the chain-hash self-check, SHA-256(uint32_be(period) ||
; int64_be(genesis_time) || public_key || genesis_seed || network), network
; left out when it is "default" (ERR_PROFILE_MISMATCH).
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 => period,             ; seconds; spec section 11: 1..max-safe-uint
  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). The same header,
; schema version 1, in all three capsule formats.
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 = control-v1 / control-v2 / control-v3

; Capsule format 1 (v0.8.2).
control-v1 = {
  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
}

; Capsule format 2 (v0.9). 103 bytes without extensions.
control-v2 = {
  0 => "datekeys-control",
  1 => 2,
  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
  6 => payload-length,     ; payload_length, L, the length of the content (spec section 29.1)
  7 => padding-scheme,     ; padding, the code of the padding rule of PAYLOAD_AGE (spec section 29.1)
}

; Capsule format 3 (v0.10). The keys of control-v2; L is the length of BODY
; (spec section 29.2). 103 bytes without extensions.
control-v3 = {
  0 => "datekeys-control",
  1 => 3,
  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
  6 => payload-length,     ; payload_length, L, the length of BODY
  7 => padding-scheme,     ; padding, the code of the padding rule of PAYLOAD_AGE
}

; Fixed width, so that the length of CONTROL_CBOR, visible in
; SEALED_CONTROL_LEN, never depends on L (spec section 55.2). Value at most
; max-payload-length (see the rules above). L = 0 is 48 0000000000000000.
payload-length = bstr .size 8
; No code stands for "no padding" (spec section 29.1).
padding-scheme = &(bloque256: 1, reforzado: 2)

; 2^53 - 2^46: the largest L whose padded length P stays within
; max-safe-uint under both padding rules (spec section 29.1).
max-payload-length = 8936830510563328

; Spec section 29.3. SECURITY_CBOR of format 3, inside the area of BODY.
; Version 1 in every later version of the spec that keeps format 3. Keys 2
; and 3 hold separately encoded CBOR, author-signature and seal, with the
; CBOR profile; a failure of their content only changes its own verdict.
; v0.11 defines alg 1 (Ed25519, spec section 29.9), alg 2 (CMS with X.509
; certificates, 29.10) and seal_type 2 (RFC 3161, 29.11); seal_type 1
; (DateKeys) and 3 (OpenTimestamps) stay reserved. A writer writes security
; empty (22 bytes) in a capsule without signature or seal, and never key 3
; with alg 2.
security = {
  0 => "datekeys-security",
  1 => 1,
  ? 2 => bstr .size (1..65536),   ; author-signature, encoded on its own
  ? 3 => bstr .size (1..65536),   ; seal, encoded on its own
}
author-signature = {
  0 => 1..4294967295,      ; alg
  1 => bstr,               ; public key
  2 => bstr,               ; signature
}
seal = {
  0 => 1..4294967295,      ; seal_type
  1 => bstr,               ; token
}

; The author-signature of each alg this version defines (spec sections 29.9
; and 29.10). A reader that does not implement an alg checks only the
; generic author-signature above.
author-signature-ed25519 = {
  0 => 1,
  1 => bstr .size 32,      ; public key A
  2 => bstr .size 64,      ; signature R || S
}
author-signature-cms = {
  0 => 2,
  1 => bstr .cbor signers, ; required signers, encoded on its own
  2 => bstr,               ; ContentInfo of type SignedData, DER, detached
}
; SHA-256 of the DER certificate of each required signer, in strictly
; ascending byte order, without repetitions.
signers = [1*16 bstr .size 32]
seal-rfc3161 = {
  0 => 2,
  1 => bstr,               ; TimeStampToken, DER
}

; Spec section 24.1. data of extension datekeys.note, version 1, in the
; noncritical array of PUBLIC_HEADER: UTF-8 text with the rules of section
; 29.6, not CBOR.
note-data = bstr .size (1..1024)

; Spec section 44.1. data of extension datekeys.capsule, version 1, in the
; noncritical array of a .dkk.
capsule-data = {
  ? 0 => tstr .size (1..1024),  ; note, a copy of the public note
  1 => tstr,                    ; compact_datekey, canonical dk1_
  ? 2 => bstr,                  ; locator: an age file with one tlock stanza
}
; Plaintext of the locator, readable at the unlock date.
capsule-locator = {
  0 => [1*16 tstr .size (1..2048)],  ; addresses (URI)
  1 => bstr .size 32,                ; capsule_digest
}

; Spec section 29.4. HEAD_CBOR of format 3, at most 16 MiB. Always version 1
; in format 3: a new version needs a new format (spec section 22). These
; limits are normative and fixed with the format.
head = {
  0 => "datekeys-head",
  1 => 1,
  2 => bstr .size 32,              ; salt, fresh from a CSPRNG
  ? 3 => tstr .size (1..16384),    ; comment (spec section 29.6)
  ? 4 => tstr .size (1..256),      ; declared_author (spec section 29.6)
  ? 5 => [1*65535 file],           ; strictly ascending UTF-8 bytes of path
  ? 6 => extensions,               ; critical_extensions
  ? 7 => extensions,               ; noncritical_extensions
}
file = {
  0 => tstr .size (1..1024),       ; path (spec section 29.5)
  1 => 0..max-payload-length,      ; size
  2 => 0..max-payload-length,      ; start
  3 => 0..max-payload-length,      ; end, exclusive
  4 => bstr .size 32,              ; SHA-256 of the file
  ? 5 => 0..253402300799,          ; mtime, UTC seconds, informative
}

; 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

; Names of the Provider Profile (spec section 12.1): the alphabets are
; normative, the maximum lengths of 128 and 64 bytes are implementation
; limits of the reference (spec section 74). A violation is
; ERR_UNKNOWN_PROFILE (spec section 57). profile-id also bounds the network
; of a dk1_ DateKey (ERR_DATEKEY_INVALID there), whose canonical JSON has no
; escapes (spec section 18).
profile-id = tstr .regexp "[a-z0-9][a-z0-9:._-]{0,127}"
name = tstr .regexp "[a-z0-9][a-z0-9._-]{0,63}"

; Spec section 31: at least 1 byte of valid UTF-8, normative; at most 256
; bytes, an implementation limit of the reference (spec section 74).
extension-id = tstr .size (1..256)

; Implementation limits of the reference implementation, listed in spec
; section 74, which leaves definitive field limits open.
public-key = bstr .size (1..1024)   ; spec section 12.1: 48 or 96 bytes by scheme
period = 1..86400          ; at most one day; spec section 11: 1..max-safe-uint

; 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.
; Spec section 15 further bounds the round time of the round to
; 9999-12-31T23:59:59Z under the pinned profile (step 7 of section 63). A
; violation is ERR_DATEKEY_INVALID or ERR_DATEKEY_NON_CANONICAL (spec section
; 19), checked with the fields, not ERR_NON_CANONICAL_CBOR.
compact-datekey = tstr .regexp "dk1_[A-Za-z0-9_-]+"