Lazy loading of crypto objects

beacon_chain/spec/beaconstate.nim

@@ -238,7 +238,7 @@ proc initialize_beacon_state_from_eth1*(
           # This differs from the spec intentionally.
           # We must specify the default value for `ValidatorSig`
           # in order to get a correct `hash_tree_root`.
-          randao_reveal: ValidatorSig(kind: OpaqueBlob)
+          randao_reveal: ValidatorSig(kind: ToBeChecked)
         ))
       )
   )
@@ -301,8 +301,8 @@ func get_initial_beacon_block*(state: BeaconState): SignedBeaconBlock =
       slot: GENESIS_SLOT,
       state_root: hash_tree_root(state),
       body: BeaconBlockBody(
-        # TODO: This shouldn't be necessary if OpaqueBlob is the default
-        randao_reveal: ValidatorSig(kind: OpaqueBlob)))
+        # TODO: This shouldn't be necessary if ToBeChecked is the default
+        randao_reveal: ValidatorSig(kind: ToBeChecked)))
       # parent_root, randao_reveal, eth1_data, signature, and body automatically
       # initialized to default values.
   SignedBeaconBlock(message: message, root: hash_tree_root(message))

beacon_chain/spec/crypto.nim

@@ -45,17 +45,23 @@ const
   RawPrivKeySize* = 48
 
 type
-  BlsValueType* = enum
+  BlsValueKind* = enum
+    ToBeChecked
     Real
-    OpaqueBlob
+    InvalidBLS
+    OpaqueBlob # For SSZ testing only
 
   BlsValue*[N: static int, T] = object
-    # TODO This is a temporary type needed until we sort out the
-    # issues with invalid BLS values appearing in the SSZ test suites.
-    case kind*: BlsValueType
+    ## This is a lazily initiated wrapper for the underlying cryptographic type
+    ## Note, since 0.20 case object transition are very restrictive
+    ## and do not allow to preserve content (https://github.com/nim-lang/RFCs/issues/56)
+    ## Fortunately, the content is transformed anyway if the object is valid
+    ## but we might want to keep the invalid content at least for logging before discarding it.
+    ## Our usage requires "-d:nimOldCaseObjects"
+    case kind*: BlsValueKind
     of Real:
       blsValue*: T
-    of OpaqueBlob:
+    of ToBeChecked, InvalidBLS, OpaqueBlob:
       blob*: array[N, byte]
 
   ValidatorPubKey* = BlsValue[RawPubKeySize, blscurve.PublicKey]
@@ -75,7 +81,30 @@ type
 
   SomeSig* = TrustedSig | ValidatorSig
 
+func unsafePromote*[N, T](a: ptr BlsValue[N, T]) =
+  ## Try promoting an opaque blob to its corresponding
+  ## BLS value.
+  ##
+  ## ⚠️ Warning - unsafe.
+  ## At a low-level we mutate the input but all API like
+  ## bls_sign, bls_verify assume that their inputs are immutable
+  if a.kind != ToBeChecked:
+    return
+
+  # Try if valid BLS value
+  var buffer: T
+  let success = buffer.fromBytes(a.blob)
+
+  # Unsafe hidden mutation of the input
+  if true:
+    a.kind = Real # Requires "-d:nimOldCaseObjects"
+    a.blsValue = buffer
+  else:
+    a.kind = InvalidBLS
+
 func `==`*(a, b: BlsValue): bool =
+  unsafePromote(a.unsafeAddr)
+  unsafePromote(b.unsafeAddr)
   if a.kind != b.kind: return false
   if a.kind == Real:
     return a.blsValue == b.blsValue
@@ -96,12 +125,7 @@ func toPubKey*(privkey: ValidatorPrivKey): ValidatorPubKey =
   ## Create a private key from a public key
   # Un-specced in either hash-to-curve or Eth2
   # TODO: Test suite should use `keyGen` instead
-  when ValidatorPubKey is BlsValue:
-    ValidatorPubKey(kind: Real, blsValue: SecretKey(privkey).privToPub())
-  elif ValidatorPubKey is array:
-    privkey.getKey.getBytes
-  else:
-    privkey.getKey
+  ValidatorPubKey(kind: Real, blsValue: SecretKey(privkey).privToPub())
 
 func aggregate*(x: var ValidatorSig, other: ValidatorSig) =
   ## Aggregate 2 Validator Signatures
@@ -119,8 +143,11 @@ func blsVerify*(
   ## The proof-of-possession MUST be verified before calling this function.
   ## It is recommended to use the overload that accepts a proof-of-possession
   ## to enforce correct usage.
+  unsafePromote(pubkey.unsafeAddr)
+  unsafePromote(signature.unsafeAddr)
+
   if signature.kind != Real:
-    # Invalid signatures are possible in deposits (discussed with Danny)
+    # InvalidBLS signatures are possible in deposits (discussed with Danny)
     return false
   if pubkey.kind != Real:
     # TODO: chronicles warning
@@ -164,13 +191,15 @@ func blsFastAggregateVerify*(
   #           in blscurve which already exists internally
   #         - or at network/databases/serialization boundaries we do not
   #           allow invalid BLS objects to pollute consensus routines
+  unsafePromote(signature.unsafeAddr)
   if signature.kind != Real:
     return false
   var unwrapped: seq[PublicKey]
-  for pubkey in publicKeys:
-    if pubkey.kind != Real:
+  for i in 0 ..< publicKeys.len:
+    unsafePromote(publicKeys[i].unsafeAddr)
+    if publicKeys[i].kind != Real:
       return false
-    unwrapped.add pubkey.blsValue
+    unwrapped.add publicKeys[i].blsValue
 
   fastAggregateVerify(unwrapped, message, signature.blsValue)
 
@@ -223,12 +252,9 @@ func fromRaw*[N, T](BT: type BlsValue[N, T], bytes: openArray[byte]): BlsResult[
     # Only for SSZ parsing tests, everything is an opaque blob
     ok BT(kind: OpaqueBlob, blob: toArray(N, bytes))
   else:
-    # Try if valid BLS value
-    var val: T
-    if fromBytes(val, bytes):
-      ok BT(kind: Real, blsValue: val)
-    else:
-      ok BT(kind: OpaqueBlob, blob: toArray(N, bytes))
+    # Lazily instantiate the value, it will be checked only on use
+    # TODO BlsResult is now unnecessary
+    ok BT(kind: ToBeChecked, blob: toArray(N, bytes))
 
 func fromHex*(T: type BlsCurveType, hexStr: string): BlsResult[T] {.inline.} =
   ## Initialize a BLSValue from its hex representation

tests/helpers/debug_state.nim

@@ -20,6 +20,8 @@ proc `==`*(a, b: BlsValue): bool =
   ## We sometimes need to compare real BlsValue
   ## from parsed opaque blobs that are not really on the BLS curve
   ## and full of zeros
+  unsafePromote(a.unsafeAddr)
+  unsafePromote(b.unsafeAddr)
   if a.kind == Real:
     if b.kind == Real:
       a.blsvalue == b.blsValue

tests/test_zero_signature.nim

@@ -39,7 +39,7 @@ suiteReport "Zero signature sanity checks":
   timedTest "SSZ serialization roundtrip of SignedBeaconBlockHeader":
 
     let defaultBlockHeader = SignedBeaconBlockHeader(
-      signature: ValidatorSig(kind: OpaqueBlob)
+      signature: ValidatorSig(kind: ToBeChecked)
     )
 
     check: