Add C# bindings.

.gitignore

@@ -66,3 +66,6 @@ bindings/rust/blst
 bindings/python
 bindings/java
 bindings/node.js
+
+bin/
+obj/

.lgtm.yml

@@ -13,3 +13,8 @@ extraction:
       build_command:
       - (cd bindings/go; go test -c)
 
+  csharp:
+    index:
+      buildless: true
+      nuget_restore: false
+

bindings/c#/poc.cs

@@ -0,0 +1,79 @@
+using System;
+using System.Text;
+using supranational;
+
+class PoC {
+  private static void Main(string[] args)
+  {
+    var msg = Encoding.UTF8.GetBytes("assertion");
+    var DST = "MY-DST";
+
+    var SK = new blst.SecretKey();
+    SK.keygen(Encoding.UTF8.GetBytes(new string('*', 32)));
+
+    // generate public key and serialize it...
+    var pk_for_wire = new blst.P1(SK).serialize();
+
+    // sign |msg| and serialize the signature...
+    var sig_for_wire = new blst.P2().hash_to(msg, DST, pk_for_wire)
+                                    .sign_with(SK)
+                                    .serialize();
+
+    // now on "receiving" side, start with deserialization...
+    var _sig = new blst.P2_Affine(sig_for_wire);
+    var _pk = new blst.P1_Affine(pk_for_wire);
+    if (!_pk.in_group())
+        throw new blst.Exception(blst.ERROR.POINT_NOT_IN_GROUP);
+    var ctx = new blst.Pairing(true, DST);
+    var err = ctx.aggregate(_pk, _sig, msg, pk_for_wire);
+    if (err != blst.ERROR.SUCCESS)
+        throw new blst.Exception(err);
+    ctx.commit();
+    if (!ctx.finalverify())
+        throw new blst.Exception(blst.ERROR.VERIFY_FAIL);
+    Console.WriteLine("OK");
+
+    // exercise .as_fp12 by performing equivalent of ctx.finalverify above
+    var C1 = new blst.PT(_sig);
+    var C2 = ctx.as_fp12();
+    if (!blst.PT.finalverify(C1, C2))
+        throw new blst.Exception(blst.ERROR.VERIFY_FAIL);
+
+    // test integers as scalar multiplicands
+    var p = blst.G1();
+    var q = p.dup().dbl().dbl().add(p);
+    if (!p.mult(5).is_equal(q))
+       throw new ApplicationException("disaster");
+    if (!blst.G1().mult(-5).is_equal(q.neg()))
+       throw new ApplicationException("disaster");
+
+    // low-order sanity check
+    var p11 = new blst.P1(fromHexString("80803f0d09fec09a95f2ee7495323c15c162270c7cceaffa8566e941c66bcf206e72955d58b3b32e564de3209d672ca5"));
+    if (p11.in_group())
+       throw new ApplicationException("disaster");
+    if (!p11.mult(11).is_inf())
+       throw new ApplicationException("disaster");
+  }
+
+  private static int fromHexChar(char c)
+  {
+    if      (c>='0' && c<='9')  return c - '0';
+    else if (c>='a' && c<='f')  return c - 'a' + 10;
+    else if (c>='A' && c<='F')  return c - 'A' + 10;
+    throw new ArgumentOutOfRangeException("non-hex character");
+  }
+
+  private static byte[] fromHexString(string str)
+  {
+    if (str.Length%2 != 0)
+        throw new ArgumentException("odd number of characters in hex string");
+
+    char[] hex = str.ToCharArray();
+    byte[] ret = new byte[hex.Length/2];
+
+    for (int i=0; i<hex.Length; i+=2)
+        ret[i/2] = (byte)(fromHexChar(hex[i]) << 4 | fromHexChar(hex[i+1]));
+
+    return ret;
+  }
+}

bindings/c#/poc.csproj

@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
+  </PropertyGroup>
+
+</Project>