Conversion of public key to bytes

abc.nimble

@@ -3,6 +3,7 @@ author = "ABC Authors"
 description = "Asynchronous Blockchain"
 license = "MIT"
 
+requires "questionable >= 0.10.0 & < 0.11.0"
 requires "https://github.com/markspanbroek/nim-blscurve#fix-nimble"
 requires "nimcrypto"
 requires "stew"

abc/keys.nim

@@ -1,5 +1,6 @@
 import pkg/blscurve as bls
 import pkg/nimcrypto
+import pkg/questionable
 
 type
   PrivateKey* = distinct bls.SecretKey
@@ -32,3 +33,15 @@ func verify*(key: PublicKey,
   ## modified BLS multi-signature construction as described in:
   ## https://crypto.stanford.edu/~dabo/pubs/papers/BLSmultisig.html
   bls.PublicKey(key).verify(message, bls.Signature(signature))
+
+func toBytes*(key: PublicKey): seq[byte] =
+  var bytes: array[48, byte]
+  doAssert serialize(bytes, bls.PublicKey(key))
+  @bytes
+
+func fromBytes*(_: type PublicKey, bytes: openArray[byte]): ?PublicKey =
+  var key: bls.PublicKey
+  if key.fromBytes(bytes):
+    PublicKey(key).some
+  else:
+    PublicKey.none

tests/testKeys.nim

@@ -1,4 +1,5 @@
 import std/unittest
+import pkg/questionable
 import pkg/stew/byteutils
 import abc/keys
 
@@ -29,8 +30,19 @@ suite "Keys":
   test "can be used to verify signatures":
     let message1 = "hello".toBytes
     let message2 = "hallo".toBytes
-    let private = PrivateKey.random()
+    let private = PrivateKey.random
     let public = private.toPublicKey
     let signature = private.sign(message1)
     check public.verify(message1, signature)
     check not public.verify(message2, signature)
+
+  test "public key can be converted to bytes":
+    let key = PrivateKey.random.toPublicKey
+    let bytes = key.toBytes
+    check PublicKey.fromBytes(bytes) == key.some
+
+  test "conversion from bytes to public key can fail":
+    let key = PrivateKey.random.toPublicKey
+    let bytes = key.toBytes
+    let invalid = bytes[1..^1]
+    check PublicKey.fromBytes(invalid) == PublicKey.none