ucan.ipldsch

type UCAN struct {
  v String

  iss Principal
  aud Principal
  s Signature

  att [Capability]
  -- All proofs are links, however you could still inline proof
  -- by using CID with identity hashing algorithm
  prf [&UCAN]
  exp Int

  fct [Fact]
  nnc optional String
  nbf optional Int
} representation map {
  field fct default []
  field prf default []
}

type Capability struct {
  with Resource
  can Ability
  -- Any additional domain specific details and/or restrictions of the capability
  nb { String: Any }
}

type Fact { String: Any }

-- The resource pointer in URI format
type Resource = String

-- Must be all lower-case `/` delimeted with at least one path segment
type Ability = String

type Principal union {
  -- This specification defines principals in terms of `did:key`s (multicodec
  -- identifiers for the public key type followed by the raw bytes of the key).
  -- We represent those as raw public key bytes prefixed with public key
  -- multiformat code.
  | secp256k1  "0xe7"
  | BLS12381G1 "0xea"
  | BLS12381G2 "0xeb"
  | Ed25519    "0xed"
  | P256       "0x1200"
  | P384       "0x1201"
  | P512       "0x1202"
  | RSA        "0x1205"

  -- To accomodate additional DID methods we represent those as UTF8 encoding
  -- of the DID omitting `did:` prefix itself. E.g. `did:dns:ucan.xyz` can be
  -- represented as [0xd1d, ...new TextEncoder().encode('dns:ucan.xyz')] bytes.
  | DID "0x0d1d"
} representation bytesprefix

-- Signatures are computed by:
-- 1. Deriving JWT header & payload using DAG-JSON omitting all empty
--    optional fields (to achieve for hash consitency)
-- 2. Formating it into base64 string
-- 3. Signing via issuers private key
--
-- Signatures are encoded into a "varsig" multiformat representation:
-- <varint sig_alg_code><vairint multihash_code><varint multihash_size><bytes sig_output>
type Signature union {
  -- Algorithms here are expected to be valid "varsig" multiformat codes.
  | NonStandard "0xd000"
  | ES256K      "0xd0e7" -- secp256k1
  | BLS12381G1  "0xd0ea" -- NB: G1 is a signature for BLS-12381 G2
  | BLS12381G2  "0xd0eb" -- NB: G2 is a signature for BLS-12381 G1
  | EdDSA       "0xd0ed"
  | ES256       "0xd01200"
  | ES384       "0xd01201"
  | ES512       "0xd01202"
  | RS256       "0xd01205"
  | EIP191      "0xd191"
} representation bytesprefix

-- UCAN-IPLD spec will register non standard signature algorithms here and
-- recommend registering them as valid "varsig" multiformat codes to remove
-- need for 0xd000 varint prefix. Implementatations MAY be also augmented
-- with additional non standard signature types.
--
-- The `0xd000` prefix MUST be used if a nonstandard signature is used.
-- Nonstandrad signatures MUST be additionally prefixed with a varint of
-- the signature length, and the UTF-8 UCAN `alg` field appended afterwards.
-- Symbolically: <varint 0xd000><varint sig_size><bytes sig><utf8 alg>.