syndicate-nim/src/syndicate/capabilities.nim

# SPDX-FileCopyrightText: ☭ Emery Hemingway
# SPDX-License-Identifier: Unlicense

runnableExamples:
  from std/unittest import check
  let sturdy = mint()
  check $sturdy == """<ref {oid: "syndicate" sig: #x"69ca300c1dbfa08fba692102dd82311a"}>"""

import std/options
from std/sequtils import toSeq
import hashlib/misc/blake2

import preserves
import ./protocols/sturdy
from ./actors import Ref

export `$`

proc hmac(key, data: openarray[byte]): seq[byte] =
  count[Hmac[BLAKE2S_256]](key, data).data[0..15].toSeq

proc mint*[T](key: openarray[byte]; oid: Preserve[T]): SturdyRef[T] =
  SturdyRef[T](parameters: {
        "oid": oid,
        "sig": hmac(key, encode(oid)).toPreserve(T),
      }.toDictionary,
    )

proc mint*(): SturdyRef[Ref] =
  var key: array[16, byte]
  mint(key, toPreserve("syndicate", Ref))

proc attenuate*[T](r: SturdyRef[T]; caveats: seq[Caveat]): SturdyRef[T] =
  result = SturdyRef[T](
    oid: r.oid,
    caveatChain: r.caveatChain,
    sig: hmac(r.sig, encode caveats))
  result.caveatChain.add caveats

proc validate*[T](key: openarray[byte]; sturdy: SturdyRef[T]): bool =
  let oid = step(sturdy.parameters, Symbol"oid")
  if oid.isSome:
    let ctrl = step(sturdy.parameters, Symbol"sig")
    if ctrl.isSome:
      var sig = hmac(key, oid.get.encode)
      let caveats = step(sturdy.parameters, Symbol"caveats")
      if caveats.isSome and caveats.get.isSequence:
        for cav in caveats.get.sequence:
          sig = hmac(sig, encode cav)
      result = (sig == ctrl.get.bytes)

when isMainModule:
  from os import commandLineParams

  var key: array[16, byte]
  case readBytes(stdin, key, 0, 16)
  of 16: discard
  of 0: stderr.writeLine "using null key"
  else: quit "expected sixteen bytes of key from stdin"

  var oids: seq[Preserve[void]]
  for p in commandLineParams():
    add(oids, parsePreserves p)
  if oids.len == 0: oids.add(toPreserve "syndicate")

  for oid in oids:
    let sturdy = mint(key, oid)
    doAssert validate(key, sturdy)
    stdout.writeLine(sturdy)