Add BLS signatures

abc.nimble

@@ -5,3 +5,4 @@ license = "MIT"
 
 requires "https://github.com/markspanbroek/nim-blscurve#fix-nimble"
 requires "nimcrypto"
+requires "stew"

abc/keys.nim

@@ -4,9 +4,11 @@ import pkg/nimcrypto
 type
   PrivateKey* = distinct bls.SecretKey
   PublicKey* = distinct bls.PublicKey
+  Signature* = distinct bls.Signature
 
 proc `==`*(a, b: PrivateKey): bool {.borrow.}
 proc `==`*(a, b: PublicKey): bool {.borrow.}
+proc `==`*(a, b: Signature): bool {.borrow.}
 
 proc random*(_: type PrivateKey): PrivateKey =
   var seed = newSeq[byte](64)
@@ -20,3 +22,13 @@ proc erase*(key: var PrivateKey) =
 proc toPublicKey*(private: PrivateKey): PublicKey =
   doAssert publicFromSecret(bls.PublicKey(result), bls.SecretKey(private))
 
+proc sign*(key: PrivateKey, message: openArray[byte]): Signature =
+  Signature(bls.SecretKey(key).sign(message))
+
+proc verify*(key: PublicKey,
+             message: openArray[byte],
+             signature: Signature): bool =
+  ## TODO: not safe w.r.t. rogue public-key attack. Needs implementation of
+  ## 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))

tests/testKeys.nim

@@ -1,4 +1,5 @@
 import std/unittest
+import pkg/stew/byteutils
 import abc/keys
 
 suite "Keys":
@@ -18,3 +19,18 @@ suite "Keys":
     check key1.toPublicKey == key1.toPublicKey
     check key2.toPublicKey == key2.toPublicKey
     check key1.toPublicKey != key2.toPublicKey
+
+  test "can be used to sign messages":
+    const message = "hello".toBytes
+    let key = PrivateKey.random()
+    let signature = key.sign(message)
+    check signature != Signature.default
+
+  test "can be used to verify signatures":
+    let message1 = "hello".toBytes
+    let message2 = "hallo".toBytes
+    let private = PrivateKey.random()
+    let public = private.toPublicKey
+    let signature = private.sign(message1)
+    check public.verify(message1, signature)
+    check not public.verify(message2, signature)