From 504e0444d3b71d1a62c0b1e917d3daecbde47a70 Mon Sep 17 00:00:00 2001
From: Giovanni Petrantoni <sinkingsugar@gmail.com>
Date: Tue, 4 Aug 2020 14:07:53 +0900
Subject: [PATCH] refactor and fix mulgen (curve25519) (#293)

* refactor and fix mulgen (curve25519)

* crypto tests fixing
---
 libp2p/crypto/curve25519.nim      | 37 +++++++++++++++++--------------
 libp2p/protocols/secure/noise.nim |  2 +-
 tests/testcrypto.nim              |  8 +++----
 3 files changed, 25 insertions(+), 22 deletions(-)

diff --git a/libp2p/crypto/curve25519.nim b/libp2p/crypto/curve25519.nim
index 18580d790..304876c2f 100644
--- a/libp2p/crypto/curve25519.nim
+++ b/libp2p/crypto/curve25519.nim
@@ -80,30 +80,33 @@ proc mul*(_: type[Curve25519], dst: var Curve25519Key, scalar: Curve25519Key, po
       EC_curve25519)
   assert res == 1
 
-proc mulgen*(_: type[Curve25519], dst: var Curve25519Key, point: Curve25519Key) =
+proc mulgen(_: type[Curve25519], dst: var Curve25519Key, point: Curve25519Key): bool =
   let defaultBrEc = brEcGetDefault()
 
   var
     rpoint = point
   rpoint.byteswap()
 
-  block iterate:
-    while true:
-      block derive:
-        let
-          size = defaultBrEc.mulgen(
-            cast[pcuchar](addr dst[0]),
-            cast[pcuchar](addr rpoint[0]),
-            Curve25519KeySize,
-            EC_curve25519)
-        assert size == Curve25519KeySize
-        for forbid in ForbiddenCurveValues:
-          if dst == forbid:
-            break derive
-        break iterate
+  let
+    size = defaultBrEc.mulgen(
+      cast[pcuchar](addr dst[0]),
+      cast[pcuchar](addr rpoint[0]),
+      Curve25519KeySize,
+      EC_curve25519)
+  
+  assert size == Curve25519KeySize
 
-proc public*(private: Curve25519Key): Curve25519Key =
-  Curve25519.mulgen(result, private)
+  if dst in ForbiddenCurveValues:
+    false
+  else:
+    true
+
+proc public*(private: Curve25519Key): Result[Curve25519Key, cstring] =
+  var res: Curve25519Key
+  if Curve25519.mulgen(res, private):
+    ok(res)
+  else:
+    err("mulgen produced a forbidden key")
 
 proc random*(_: type[Curve25519Key], rng: var BrHmacDrbgContext): Curve25519Key =
   var res: Curve25519Key
diff --git a/libp2p/protocols/secure/noise.nim b/libp2p/protocols/secure/noise.nim
index c34be2973..b02ad5c4f 100644
--- a/libp2p/protocols/secure/noise.nim
+++ b/libp2p/protocols/secure/noise.nim
@@ -88,7 +88,7 @@ type
 
 proc genKeyPair(rng: var BrHmacDrbgContext): KeyPair =
   result.privateKey = Curve25519Key.random(rng)
-  result.publicKey = result.privateKey.public()
+  result.publicKey = result.privateKey.public().tryGet()
 
 proc hashProtocol(name: string): MDigest[256] =
   # If protocol_name is less than or equal to HASHLEN bytes in length,
diff --git a/tests/testcrypto.nim b/tests/testcrypto.nim
index 287e6bd04..0632264f8 100644
--- a/tests/testcrypto.nim
+++ b/tests/testcrypto.nim
@@ -505,14 +505,14 @@ suite "Key interface test suite":
 
     # RFC vectors
     private1 = fromHex("a8abababababababababababababababababababababababababababababab6b").intoCurve25519Key
-    check private1.public().toHex  == "E3712D851A0E5D79B831C5E34AB22B41A198171DE209B8B8FACA23A11C624859"
+    check private1.public().get().toHex  == "E3712D851A0E5D79B831C5E34AB22B41A198171DE209B8B8FACA23A11C624859"
     private1 = fromHex("c8cdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcd4d").intoCurve25519Key
-    check private1.public().toHex  == "B5BEA823D9C9FF576091C54B7C596C0AE296884F0E150290E88455D7FBA6126F"
+    check private1.public().get().toHex  == "B5BEA823D9C9FF576091C54B7C596C0AE296884F0E150290E88455D7FBA6126F"
     private1 = fromHex("77076d0a7318a57d3c16c17251b26645df4c2f87ebc0992ab177fba51db92c2a").intoCurve25519Key
     var
       private2 = fromHex("5dab087e624a8a4b79e17f8b83800ee66f3bb1292618b6fd1c2f8b27ff88e0eb").intoCurve25519Key
-      p1Pub = private1.public()
-      p2Pub = private2.public()
+      p1Pub = private1.public().get()
+      p2Pub = private2.public().get()
     check p1Pub.toHex  == "8520F0098930A754748B7DDCB43EF75A0DBF3A0D26381AF4EBA4A98EAA9B4E6A"
     check p2Pub.toHex  == "DE9EDB7D7B7DC1B4D35B61C2ECE435373F8343C85B78674DADFC7E146F882B4F"